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- Tc truyn sng c hay tc nh sng.- Tn s (hec): s ln bc sng truyn qua mt im trong khng gian trong mt

n v thi gian.

. = c

- Chu k T (s): thi gian ngn nht truyn mt bc sng qua mt im trong khng

gian.

- Trong quang ph ngi ta cn dng i lng nghch o ca bc sng 1/ o

chiu di ca bc sng, k hiu )(1 1 cm

Cc bc x in t cng mang nng lng, cc bc x c chiu di bc sng cng

nh th nng lng ca chng cng ln v tun theo nh lut:

chhE

..

Trong : h l hng s planck. h = 6,6262.10-34 J.s

Nng lng E c o bng n v eV, kcal/mol, cal/mol.Khi cc bc x in t tng tc vi cc phn t vt cht, c th xy ra theo hai kh

nng: trng thi nng lng ca phn t thay i hoc khng thay i. Khi c s thay i

nng lng th phn t c th hp th hoc bc x nng lng.

Nu gi trng thi nng lng ban u ca phn t l E1, sau khi tng tc l E2 th

c th vit:

E = E2 E1

: bc sng

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E = 0: nng lng phn t khng thay i khi tng tc vi bc x in t.

E > 0: phn t hp th nng lng; E < 0: phn t bc x nng lng.

Theo thuyt lng t th cc phn t v bc x in t trao i nng lng vi nhaukhng phi bt k v lin tc m c tnh cht gin on. Phn t ch hp th hoc bc x 0,

1, 2, 3n ln lng t h.. Khi phn t hp th hoc bc x s lm thay i cng ca

bc x in t nhng khng lm thay i nng lng ca bc x in t, bi v cng

bc x in t xc nh bng mt cc ht photon c trong chm tia cn nng lng ca

bc x in t li ph thuc vo tn s ca bc x. V vy, khi chiu mt chm bc x

in t vi mt tn s duy nht i qua mi trng vt cht th sau khi i qua nng lng ca

bc x khng h thay i m ch c cng ca bc x thay i.

Khi cc phn t hp th nng lng t bn ngoi c th dn n cc qu trnh thay

i trong phn t (quay, dao ng, kch thch electron phn t) hoc trong nguyn t

(cng hng spin electron, cng hng t ht nhn).

Cc trng thi kch thch phn t

Mi mt qu trnh nh vy u i hi mt nng lng E > 0 nht nh c trng

cho n, ngha l i hi bc x in t c mt tn s ring gi l tn s quay q, tn s dao

ng d v tn s kch thch in t .

V th khi chiu mt chm bc x in t vi cc tn s khc nhau vo th cc phn

t ch hp th c cc bc x in t c tn s ng bng cc tn s trn (q, d v )

xy ra cc qu trnh bin i trong phn t nh trn. Do s hp th chn lc ny m khi

chiu chm bc x in t vi mt di tn s khc nhau i qua mi trng vt cht th sau

khi i qua, chm bc x ny s b mt i mt s bc x c tn s xc nh ngha l cc tia

ny b phn t hp th.

quay Dao ng

Kch thch electron

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1.3. nh lut Lambert Beer

Khi chiu mt chng tia sng n sc i qua mt mi trng vt cht th cng

ca tia sng ban u I0 s b gim i ch cn l I.Nng lng nh sng: E = h. = h.c/

Nng lng ca nh sng ph thuc vo .

Cng nh sng I ph thuc vo bin dao ng a.

d: dy

Vi hai tia sng c cng nng lng nhng c cng nh sng khc nhau

T = I/I0.100%: truyn qua

A = (I0 I)/I0.100%: hp th

ln ca truyn qua T hay hp th A ph thuc vo bn cht ca cht ha

tan, chiu dy d ca lp mng v nng C ca dung dch. Do , c th vit:

Lg(I0/I) = .C.d = D

= D/C.d; lg = lgD/C.d

c gi l h s hp th, C c tnh bng mol/l, d tnh bng cm v D l mt

quang. Phng trnh trn ch ng vi tia n sc.

1.4. Ph

- Khi cho bc x in t tng tc vi phn t vt cht, dng thit b my ph ghi

nhn s tng tc , ta nhn c mt dng th gi l ph.

- T nh lut Lambert-Beer, ngi ta thit lp v biu din s ph thuc:

+ Trn trc tung: A, D, , lg, T

+ Trn trc honh: tn s bc x , s sng , bc sng bc x kch thch

Thu c th c dng D = f(), lg = f(), T = f(), A = f() th ny gi l

ph. Cc nh hp ph cc i gi l di (band) hay nh hp th (peak), chiu cao ca nh

peak gi l cng hp th.

I0 I

d

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Ring vi ph NMR v ph MS th i lng trn trc honh c m rng hn

thnh chuyn dch ha hc (ppm) hay s khi m/e.

1.5. ng cong hp th v phn gii- S ph thuc ca D vo bc sng: D = f()

Khi = const; d = const th D = f(C)

Dng phng trnh ny phn tch nh lng.

Vi cng mt cht nhng vi cc tia sng khc nhau s cho cc ng th khc

nhau.

- S ph thuc ca h s hp th vo chiu di ca bc sng kch thch.ng cong

biu din s ph thuc ny gi l ph. Cc nh hp th cc i gi l di hay nh hp th,

chiu cao ca nh hp th gi l cng .

= f() hay lg = f() khi C = const; d = const

ng cong c cc i v cc tiu V tr ca cc max v max ging nhau

Khng ph thuc vo nng C Mi gi tr ca C c mt th khc nhau

D

C [mg/l]

maxD

C [mol/l]

C

C

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Hai ng biu din ny dng phn tch cu to ca cc hp cht.

Cc nh hp th c khi c tch ra khi nhau hon ton nhng c nhiu khi chng

chng ln nhau mt phn hay gn nh hon ton. S tch bit ny ph thuc vo kh nngtch bit ca tng my m c gi l kh nng phn gii ca my. Ngi ta nh ngha

phn gii R ca my l kh nng tch bit hai nh hp th c chiu di bc sng v +

. R = /.

1.6. Vng ph Quang hc

Bc x in t bao gm mt vng chiu di sng rt rng, nhng kch thch cc

qu trnh quay, dao ng v kch thch electron ch c mt vng bc sng hp t 1mm n

100A hay 10-1 n 10-6cm. Ph thuc vo vic s dng vt liu quang hc, ngi ta phnchia cc vng nh sng nh sau:

- Vng sng 50 1200 A0. Dng vt liu quang hc l cch t v khng th s dng

vt liu trong sut. Khng c ngha i vi ha hc hu c.

- Vng sng 1200 1850 A0. Dng vt liu quang hc l CaF2. Cc tia sng thu nhn

c bng knh nh. ng dng nghin cu cc hp cht ha hc.

- Vng sng 1850 4000 A0 (vng t ngoi trung bnh). Vt liu quang hc l thch

anh. Vng ny chnh vng quang ph ngoi, c ng dng rng ri nghin cu cc hp

cht. Ngun sng l en deuteri.

- Vng sng 4000 8000 A0 (vng nhn thy). Vt liu quang hc l thy tinh, ngun

sng l n in thng (vonfram hay tungsten). Vng ny c s dng nghin cu cc

hp cht c mu.

- Vng sng 0,8 - 2m (vng hng ngoi gn). Vt liu quang hc c th l thy tinh

hay thch anh. Ngun sng n in thng.

- Vng 2 - 40m (vng hng ngoi c bn). Vt liu quang hc dng ng thi l LiF

(n 6m), CaF2 (n 9m), NaCl (n 15 m), KBr (n 27 m), CsI (n 40 m). Ngun

sng dng n Nernst. C ngha thc t ln nghin cu cc hp cht ha hc.

- Vng sng 40 200 m (vng hng ngoi xa). Vt liu quang hc dng cch t.

1.7. S khi ca ph k quang hc

S khi ca ph k quang hc gm cc b phn chnh sau:

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(1) Ngun sng: ty thuc vo mi loi ph k m c cc ngun sng ring. V d,

ph k hng ngoi dng ngun pht bc x hng ngoi, ph k t ngoi dng ngun pht

bc x t ngoi.

(2) Cuvet mu:

(3) B chn sng: c th dng knh lc hay b n sc (vi lng knh hay cch t)

tch bc x a sc thnh bc x n sc.(4) Detect: b phn pht hin tn hiu, bin tn hiu quang thnh tn hiu in. C

nhiu loi detect khc nhau nh Vonteic, detect ng nhn quang, detect chuyn in tch,

detect cp nhit in, detect ha nhit.

(5) Khuych i tn hiu

(6) B phn c tn hiu: ng h in k, b hin s, b t ghi, my tnh

V mt thit k, ngi ta ch to hai kiu my: kiu mt chm tia v kiu hai chm

tia. Trc kia kiu mt chm tia ch s dng o tng im ca chiu di sng dng cho phntch nh lng cn kiu hai chm tia c th qut ng thi c mt vng chiu di sng lin

tc. Ngy nay, do vic s dng my tnh lu tr v c tn hiu cho nn cc my mt

chm tia c thit k cho c mt ph lin tc nh my hai chm tia.

(1) (2) (3) (4) (5) (6)

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CHNG 2. PH HNG NGOI

2.1. Cc nguyn l c bn ca ph hng ngoiKhi cc phn t hp th nng lng t bn ngoi c th dn n qu trnh quay, dao

ng xung quanh v tr cn bng ca n. Ty theo nng lng kch thch ln hay nh c th

xy ra qu trnh quay, dao ng hay c quay v dao ng ng thi. kch thch cc qu

trnh trn c th s dng tia sng vng hng ngoi (ph hng ngoi) hoc tia khuych tn

Raman (ph Raman).

Bc x hng ngoi lin quan n phn ph in t nm gia vng kh kin v vng

vi sng c bc sng nm trong vng: vng hng ngoi gn: 14290 4000 cm-1

v hngngoi xa: 700 200 cm-1. Vng ph c ngha quan trng nht l vng gia 4000 v 400

cm-1.

2.1.1. S xut hin ca quang ph quay

i vi cc phn t gm hai nguyn t c khi lng khc nhau (nh CO, HCl) c

0 c th xp vo mu quay ca hai qu t c khi lng m1 v m2. Gi thuyt v trong qu

trnh quay th khong cch gia hai nguyn t khng thay i.

Khi phn t gm hai nguyn t quay theo mt hng trong khng gian th momen

qun tnh I ca qu trnh c tnh theo biu thc:

I = mr02

Vi r0 = r1 + r2

V21

21

mm

mmm

Theo c hc lng t th nng long quay Eq ca cc phn t gm hai nguyn t

c tnh theo phng trnh:

m1m

r

r1 r2

0

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jq EJJIh

E )1(8 2

2

Trong I v mmen qu trnh, h l hng s Planck, J l s lng t quay v J =

1,2,3

Chia hai v ca phng trnh cho hc c:

)1(8 2 JJ

Ic

h

hc

EF jj

tIc

hB

28 th phng trnh trn c dng:

Fj = BJ(J+1)

B c gi l s lng t quay v Fj l s hng quay.

S ph thuc ca Fj v Fj vo J

Fj = Fj Fj = q

Bc chuyn di nng lng trong qu trnh quay ca phn t gm hai nguyn t

tun theo quy tt J=1. Do :

)1(2

)1()1'(''

JB

JBJJBJhc

E

hc

E

q

jjq

kch thch phn t quay, ngi ta thng dng ngun vi sng cho nn ph ny

c gi l ph vi sng hoc dng tia sng vng hng ngoi xa cho nn ngi ta cn gi

quang ph quay l quang ph hng ngoi xa.

2.1.2. S xut hin ca quang ph dao ng

i vi cc phn t gm hai nguyn t (CO, HCl), ngi ta xp vo mu hai hn bi

ni vi nhau bi mt chic l xo. Khong cch bnh thng gia hai hn bi l r0, nu gi

cht mt hn bi v ko hn bi kia ra mt on dr ri th t do th n s dao ng quanh v tr

cn bng vi bin dr khng i. Mu ny c gi l dao ng t iu ha.

Nng lng ca dao ng t iu ha c tnh theo phng trnh:

2)(2

1drkEt

Do khi dr = 0 th Et = 0, ngha l khi dao ng t trng thi cn bng th nng

lng ca n bng 0. ng cong th nng ca n l mt ng parabol c cc tiu ti r0.

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Theo c hc c in th tn s dao ng iu ha c tnh theo phng trnh:

M

k

2

1

Vi k l hng s lc v M l khi lng rt gn.

Theo c hc lng t, khi cc phn t dao ng chng ch c th chim tng mc

nng lng nht nh cha khng thay i lin tc v phng trnh nng lng ca phn t

thc c tnh theo cng thc:

EvhEt

2

1

Vi v = 0,1,2 c gi l s lng t dao ng

Khi v = 0 th Ev 0, nh vy khi phn t khng dao ng n vn cha mt nng

lng nht nh v gi l nng lng im khng.

E = E2 E1 = h[v + 1 + - (v + )]

E = h : khng ph thuc vo v.

V phn t thc khng dao ng iu ha (dao ng vi bin thay i) nn

phng trnh nng lng ca n c b chnh theo cng thc:

21

421 22 v

DvhvhEv

D l nng lng phn li ca phn t.

Quy tt la chn vi phn t dao ng v = 1, 2 Nh vy khi phn t dao ng

c th tip nhn cc bc chuyn nng lng sau:

v = 0 v = 1 gi l dao ng c bn

v = 0 v = 2 gi l dao ng cao mc 1



.

v = 0 v = n gi l dao ng cao mc n -1

Tuy nhin, xc sut ca cc bc chuyn ny (cng vch ph) gim dn khi bc

dao ng tng.

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Khi phn t phn li thnh ion th v tng nhng E khng tng.

2.1.3. Dao ng quay ca phn t

Khi kch thch nng lng thch hp thng xy ra qu trnh phn t va quay va

dao ng gi l dao ng quay ca phn t. Nng lng dao ng quay bng tng nng

lng quay v nng lng dao ng:

Edq = Eq + Ed = (v + 1/2)hv + BhcJ(J + 1)i vi phn t dao ng quay phi tun theo quy tc la chn J = 1 v v = 1

i vi phn t thc phi c h s iu chnh.

Nhnh R J = +1

v = +1

Ph hp vi quy lut cm

P J = -1

v = +1

Ph hp vi quy lut cm

im Q J = 0

v = +1

Khng xy ra s kch thch

Theo quy tt la chn trn, ph dao ng quay ca cc phn t gm hai nguyn t c

hai nhnh Pv R im Q = 0.

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2.1.4. Dao ng chun ca phn t

Cc nguyn t trong phn t dao ng theo ba hng gi l dao ng chun ca phn

t. i vi phn t c cu to nm trn ng thng, s dao ng chun ca phn t c Nnguyn t ti a bng 3N 5 v 3N 6 i vi phn t khng thng.

Mi dao ng chun c mt nng lng nht nh, tuy nhin c trng hp 2, 3 dao

ng chun c mt mc nng lng . Cc dao ng chun c cng mt mc nng lng gi

l dao ng thoi bin.

Ngi ta phn bit dao ng chun thnh hai loi:

- Dao ng ha tr (k hiu l ) l nhng dao ng lm thay i chiu di lin kt ca

cc nguyn t trong phn t nhng khng lm thay i gc lin kt.

- Dao ng bin dng (k hiu ) l nhng dao ng lm thay i gc lin kt nhng

khng lm thay i chiu di lin kt ca cc nguyn t trong phn t.

Mi loi dao ng cn c phn chia thnh dao ng i xng v bt i xng.

V d:

- Phn t CO2 thng c 3N 5 = 3.3 5 = 4 dao ng chun trong c 2 dao ng

ha tr (mt i xng v mt bt i xng) v 2 dao ng bin dng i xng.

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- Phn t nc khng thng c 3N 6 = 3.3 6 = 3 dao ng chun trong c hai

dao ng ha tr v mt dao ng bin dng i xng.

iu kin kch thch dao ng:Khng phi khi no c nh sng chiu vo phn t cng c ph hng ngoi. Khi nh

sng chiu vo phn t, phn t dao ng, trong qu trnh dao ng momen lng cc ca

phn t khc 0 v phn cc ca phn t khng i mi xut hin ph. Nu mmen

lng cc bng 0 v phn cc khc 0 th ph hng ngoi khng hot ng.

2.2. S lin quan gia tn s hp th v cu to phn t

2.2.1. Cc nh hng lm dch chuyn tn s c trng

Tn s dao ng ca cc nguyn t ph thuc vo hng s lc ca lin kt v khilng ca chng. Do cc nhm chc khc nhau c tn s hp th khc nhau v nm trong

vng t 5000 200 cm-1.

nh hng ca dung mi, nng , nhit v trng thi tp hp n v tr ca cc

cc i hp th.

- Dung mi: c nh hng n s thay i v tr ca cc cc i hp th ty theo

phn cc ca chng

- Nng dung dch cng gy nh hng n s thay i v tr ca nh hp th, c

bit i vi cc cht c kh nng to cu lin kt hiro nh ancol, phenol, amin

- nh hng ca nhm th. Cc nhm th trong phn t cng gy nh hng n s

thay i v tr nh hp th ty theo nhm th gy hiu ng cm ng hay lin hp.

- Phc cht: Khi to phc, tn s hp th c trng ca nhm chc thay i theo kim

loi trung tm v s phi tr.

2.2.2. Tn s c trng ca cc nhm chc hu c

1. Ankan

Cc ankan cha nhm CH2 v CH3 trong phn t c cc dao ng c trng C-H ha

tr v bin dng.

Dao ng ha tr CH3 CH2

2850 2960 (CH) bt i xng (CH) i xng (CH) bt i xng (CH) i xng

2960 2870 2925 2850

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Dao ng bin dng

720, 1000 1465 (CH) bt i xng (CH) i xng (CH) (CH) (CH)

1460 1375 1465

720 1250

bt i xng

1045

2. Anken

Dao ng ha tr C-H 3000 cm-1

C=C 1600 1650 cm-1

3. Ankin


CC 3150 cm

-1

4. Anlenic

Dao ng ha tr C=C=C 1960 -1940 cm-1

5. Hirocacbon thm


C=C 1600, 1500, 1470 cm-1

Dao ng bin dng C-H 700 900 cm-1

Dao ng t hp (cng rt yu) 1900 1750 cm-1

6. Ancol, phenol

Dao ng ha tr: OH t do (dung dch long) nng < 0,01M: 3300 3500 cm-1 (3600)

OH t do (dung dch c) nng > 1M: 2500 3200 cm-1

C-O 1100 1300 cm-1

7. Andehyt/xetonDao ng ha tr C=O 1650 1800 cm

-1

8. Anhidrit

Dao ng ha tr C=O 1800 1870 cm-1

1750 1790 cm-1

9. Axit cacboxylic

Dao ng ha tr C=O (dime) nng bnh thng 1680 1720 cm-1

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C=O (monome) nng rt long 1740 1800 cm-1

Nhm OH ca axit OH 2500 3500 cm-1

Pic ca nhm OH ny c chn rng10. Mui axit cacboxylic


11. Clorua axit

Dao ng ha tr C=O (thng) 1795 1810 cm-1

Dao ng ha tr C=O (thm) 1765 1785 cm-1

12. Este


C-O-C 1150 1250 cm-1

13. Amin

Bc 1 NH2 hai nh 3500 3600 cm-1

NH2 1650 cm-1

C-N vng thm 1150 1200 cm-1

1030 1120 cm

-1

Bc 2 NH 1 nh 3500 cm

-1

NH 1650 cm-1

C-N 1150 1200 cm-1

1080 1150 cm-1

Bc 3 C-N 1130 1230 cm-1

1030 1120 cm-1

14. Amit

C=O amit I 1600 1690 cm-1

N-H amit II 1500 1600 cm-1

N-H 3500 v 3600 cm-1 (-NH2)

3500 cm-1 (-NH-)

15. Nitro

Dao ng ha tr NO2 1530 cm-1

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NO2 1330 cm-1

2.3. Mt s v d gii ph hng ngoi

- Ghi tt c cc vng ph (chn peak), (nh peak). Ch cc peak c trng: cim (nh kp, mnh v rng, yu v hep, nhn v hp, chn rng v ging... )

- T cng thc phn t, d on c th cha dao ng ca nhng nhm cha no?

- Cc peak ca ph c th ng vi dao ng ca nhng nhm chc no?

- i chiu

Nu ch s dng ph IR, ng vi mt s cng thc phn t v mt ph c th d

on c nhiu cng thc cu to tng ng.

ph hng ngoi ca hecxen -1

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ph hng ngoi ca toluenph hng ngoi ca toluen

ph hng ngoi ca pentin - 1

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ph hng ngoi ca anilin

ph hng ngoi ca phenol

ph hng ngoi ca anilin

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2.4 My o ph hng ngoi

Ph k hng ngoi hin nay gm cc loi: ph k hng ngoi mt chng tia dng knh

lc, ph k hng ngoi hai chng tia tn sc v ph k hng ngoi bin i Fourier (FTIR)- Ph k hng ngoi mt chm tia dng knh lc l loi n gin dng cho phn tch

nh lng kh. Trong my c h thng quang hc v mt bm ht mu kh dng ngun

pin.

- Ph k hng ngoi hai chm tia tn sc l loi ph bin trc y, my ghi ph qut

c vng t 4000 cm-1 n 200 cm-1 c ni vi b t ghi hay my vi tnh.

S ph k hng ngoi hai chm tia tn sc t ngun sng S1 pht ra hai chm tia

song song, mt i qua mu, mt i qua cuvet so snh, sau chp li qua khe vo S3 nlng knh (hoc cch t) ri qua khe ra S4 i n detect.

+ Ngun sng cho my ph hng ngoi thng dng en Nernst (hn hp oxit kim

loi 85% ZrO2 v 15% Y2O3), n Globa (silic cacbua SiC2), n Nicrom (dy t niken

crom). Nhit t nng khong 700 8000C.

ph hng ngoi ca isobutyl nitrin

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+ Lng knh: gm 3 ci c ch to t cc vt liu KBr, NaCl v L v mi loi ch

cho mt vng nh sng hng ngoi i qua. Cch t ch to bng thy tinh, trn mi milimet

c vch t 200 n 300 vch cch u nhau.+ Detect: thng hay dng l lai detect t bo nhn quang, cp nhit in hoc ta

nhit.

Detect t bo nhn quang gm nhiu l kim loi trn ph bt kim loi nhy sng

nh selen, silic. Khi c mt photon p vo b mt kim loi s pht ra hng trm electron,

cc electron ny li chuyn ng n l kim loi th hai v mi electron p vo s pht ra

hng trm electron na v c tip tc nh vy i n cc l kim loi sau. Cui cng c hng

triu electron c pht ra t mt photon. Cc electron ny i n anot, to ra mt dng inm in th ca n t l vi cng nh sng p vo.

Detect cp nhit in c ch to t hai thanh kim loi khc nhau nh bmut v

antimoan, to ra mt in th nh khi t nng ch tip gip nhau bng bc x hng ngoi.

Ch cn c mt s thay i rt nh nhit ca bc x chiu vo lm bin thin cng

dng in sinh ra (nhit bc x thay i 10-60K, in th thay i 6 8 V/W). Detect

cp nhit in c tr khng thp nn thng c ni vi b tin khuych i c tr khng

cao.

Detect ha nhit c ch to t nhng ming n tinh th ca cc cht ha nhit.

Chng l cht cch in c tnh cht in v nhit rt c bit. Cc cht ny c kp vo

gia hai in cc ng vai tr mt t in m in dung ca n ph thuc mnh vo s thay

i nhit . Khi ni hai in cc vo mt mch in s xut hin mt dng in m in

th ca n thay i rt nhy vi s thay i nhit ca bc x hng ngoi chiu vo.

+ Cuvet: cuvet o ph hng ngoi thng c hai loi cuvet o mu lng v cuvet o

mu rn.

Cuvet o mu lng (cht tinh khit hay dung dch) c cu to gm hai tm ca s

bng NaCl, KBr hoc LiF, mt vng m gia c dy bng dy cuvet, vng m v

gi bn ngoi, mt tm ca s v gi c khoan hai l np mu. Trn cuvet c ghi

r dy lp mng dung dch bn trong, khi o phi chn cp cuvet c dy nh nhau

ng mu cht v dung mi so snh. kim tra chnh xc dy cuvet, ngi ta t mt

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cuvet khng vo my ri o trong mt vng bc sng c tn hiu ph hnh sin ri tnh

theo cng thc:

)(2 21 vv

Nd

Vi d l chiu dy ln mng. N l s nh cc i, 1 v 2 l s sng.

Cc mu kh c o bng mt cuvet c bit, v hp th ca cc kh thp nn

ng nh sng i qua mu phi di. Chiu di thc ca mi cuvet kh ch 10 cm nhng

ng nh sng i qua phi di hng met, do cn c mt h thng gng t trong cuvet

nh sng i qua li mu nhiu ln.

- Ph k hng ngoi bin i Fourier (FT-IR)Ph k hng ngoi hin i l loi ph k bin i Fourier. Loi ph k mi ny khc

loi ph k tn sc c l thay b n sc (lng knh hoc cch t) bng mt giao thoa k

Michelson nh s ch ra hnh di.

`

Cu to ca giao thoa k Michelson gm gng phng di ng M1, mt gng c

nh M2 v mt tm knh phn tch nh sng S. nh sng t ngun chiu vo tm knh S

ngun sng

M2

M1

mu o

detect

1

2

O

S

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tch lm hai phn bng nhau, mt phn chiu vo gng M1 v mt phn khc chiu vo

gng M2, sau phn x tr li qua knh S, mt na tr v ngun, cn mt na chiu qua

mu i n detect. Do gng M1 di ng lm cho on ng ca tia sng i n gngM1 ri quay tr li c di ln hn on ng tia sng i n gng M 2 ri quay tr li

v c gi l s tr. Do s tr ny lm nh sng sau khi qua giao thoa k bin i t tn

s cao xung tn s thp. Sau nh sng qua mu b hp th mt phn ri i n detect,

nh k thut bin i Fourier nhn c mt ph hng ngoi bnh thng ghi trn ph k

hng ngoi tn sc nhng c phn gii v t s tn hiu/nhiu (S/N) cao hn, ngha l ph

nhn c c cht lng tt hn, c bit thi gian ghi ph nhanh, ch khong 30 giy.

2.5. Mt s ng dngPhng php ph hng ngoi c th c ng dng trong phn tch nh lng mt

cht trong dung dch hay trong hn hp. C s ca phng php ny da trn phng trnh

nh lut Lambert Beer biu hin mi quan h gia s hp th nh sng v nng cht:

DdC

I

I ..log

0

Theo phng trnh trn, mt boc sng xc nh, s hp th nh sng t l vi nng

C v chiu dy cuvet d v bn cht ca cht mu. Nh vy, khi phn tch mt cht, o mt bc sng xc nh vi mt cuvet c chiu dy d bit th mt quang D ch cn t

l vi nng C ca mu cht. V phng trnh trn ch chnh xc vi dung dch c nng

long nn phng php phn tch nh lng bng ph hng ngoi ch p dng o trong

dung dch, cn theo phng php p mu rn (p KBr) th ch phn tch bn nh lng.

Phng php phn tch nh lng nh ph hng ngoi cng c th thc hin theo

cch lp ng chun. Pha mt lot mu vi cc nng khc nhau ca cht cn xc nh

dng tinh khit ri o gi tr D ca chng, sau v th biu din s ph thuc D vo

nng C. Vn kh khn v mc sai s trong phng php ny l tnh t s I0/I. V

nguyn tc, gi tr I0 v I c th xc nh trn ph theo cc tm ng nn ri o gi tr I0v

I. Kh khn y l xc nh ng nn sao cho sai s phng php l nh nht bi v trn

ng cong ph c s che ph nhau ca cc nh cho nn c th c mt s v tr khc nhau

khi v ng nn. V th ngoi phng php ng nn, ngi ta cn tin hnh theo mt s

phng php khc t chnh xc cao hn.

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Sau khi thit lp c th ng chun, cn ch ng chun ny ch s dng

c trong phm vi gii hn nng ng vi on thng ca ng biu din, bi v trong

gii hn ny mi c s tuyn tnh gia mt quang v nng dung dch. Sau c thxc nh nng ca dung dch mu cn tm bng cch o gi tr Dx ri chiu ln th

tm gi tr Cx.

Phng php ph hng ngoi cng c th p dng phn tch nh lng hn hp

nhng thc hin rt phc tp.

2.6. Bi tp

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CHNG 3. PH T NGOI KH KIN

Ph t ngoi v kh kin, vit tt l UV-VIS (ultraviolet-Visible) l phng php

phn tch c s dng rng ri t lu.Vng sng: t ngoi (UV) 200 400 nm

Kh kin (VIS) 400 800 nm

Ph t ngoi v kh kin ca cc cht hu c gn lin vi bc chuyn electron gia

mc nng lng electron trong phn t khi cc electron chuyn t cc obitan lin kt hoc

khng lin kt ln cc obitan phn lin kt c mc nng lng cao hn, i hi phi hp th

nng lng t bn ngoi.

Cc electron nm obitan lin kt nhy ln obitan phn lin kt * c mc nng

lng cao nht, ng vi bc sng 120 150 nm, nm vng t ngoi xa. Cc electron v

cc electron p (cp electron t do) nhy ln obitan phn lin kt * c mc nng lng ln

hn, ng vi bc sng nm trong vng t ngoi 200 400 nm hay vng kh kin 400

800 nm ty theo mch lin hp ca phn t.

Ph t ngoi v kh kin lin quan cht ch n cu to, ni i lin hp v vng

thm. c ng dng rng ri.

3.1. C s l thuyt

3.1.1. Bc chuyn di nng lng

iu kin bnh thng, cc electron trong phn t nm trng thi c bn, khi c

nh sng kch thch vi tn s thch hp th cc electron ny s hp th nng lng v

chuyn ln cc trng thi kch thch c mc nng lng cao hn. Theo c hc lng t,

trng thi c bn cc electron c sp y vo cc obitan lin kt , hay n c mc nng

lng thp, khi b kch thch s chuyn ln cc mc nng lng cao hn:

*

*

n*, *

Hiu s mc nng lng gia hai obitan chnh l nng lng hp th t ngun sng

kch thch t bn ngoi.

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Bc chuyn di nng lng (nm) Nng lng kch thch (E, kcal/mol)

* 120 230

* 160 184

n* 180 162

n* 280 82

Hiu s gia cc mc nng lng ny khc nhau. V:

hchE

Do chiu di bc sng ca cc cc i hp th s ngc li:

****

nn

Thng thng trong qu trnh kch thch electron c km theo qu trnh quay v dao

ng ca phn t, do nng lng chung ca h phn t bng tng nng lng ca cc qu

trnh trn:

edq EEEE

Trong : Ee nng lng kch thch electron.

Ed nng lng dao ng ca cc nguyn t

Eq nng lng quay

Bc nhy nng lng i vi s kch thch electron ln hn bc nhy nng lng

i vi s dao ng v ln hn bc nhy nng lng ng vi s quay phn t:

Ee >> Ed >> Eq

n

*

*

S bc chuyn nng lng ca cc electron

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3.1.2. Nhm mang mu v s lin hp ca cc nhm mang mu

Cc cht c mu l do trong phn t ca cc cht cha nhiu nhm ni i hay ni ba

nh C=C, C=O, C=N, N=N, CC, NN, -NO2 Do vy, chng c gi l nhm mangmu. Nu trong phn t c nhiu nhm mang mu lin hp to thnh mch di th mu ca

cht s cng m. Cc cht mu m khi o ph t ngoi kh kin cho max nm vng c

bc sng di. Do , nhng hp cht hu c c mch lin hp di th cc i nm pha

sng di. Cc kiu lin hp sau:

- Lin hp -

Loi ny xut hin khi trong hp cht c cha cc ni i lin hp, cc cc i hp

th chuyn dch mnh v pha sng di v cng hp th tng khi s ni i lin hptng.

(1 2)2 (1

* 2*)2

E < E1, E

2

> 1, 2

Cc i hp th tng ng vi bc chuyn di ca e * ca ni i bit lp t

quan trng v nm trong vng t ngoi chn khng l max < 180 nm nhng ca h ni i

H HH2

1 2

1 + 2

1 - 2H HH2

1 2

1 + 2

1 - 2

1

1* 2

*

2

1 + 2

1 - 2

1*+ 2

*

1*- 2*

E2E

1

E

S kiu lin hp -

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lin hp li rt quan trng lin quan cht ch vi h lin hp ca phn t v max nm trong

vng t ngoi kh kin (max > 200 nm).

Nguyn nhn ca s thay i ny l do s lin hp gia cc lin kt lm thay imc nng lng ca cc obitan (mc nng lng ca obitan lin kt c electron chim tng

ln cn mc nng lng ca obitan phn lin kt h xung lm cho nng lng ca bc

chuyn di ele4ctrron gia hai obitan gim xung do max tng ln.

Di hp th ny k hiu l K. Di K nm v pha sng ngn nhng cng hp th

ln ( ~ 104).

Ca etilen cho nh hp th cc i 175 nm ca butadien 217 nm cn ca

hecxatrien 274 nm.

i vi vng benzen cn xut hin di hp th ng vi bc chuyn di ca h thng

electron c bc sng 256 nm c gi l di B.

- Lin hp - p

y l s lin hp ca ni i v cp electron t do cc d t trong cc lin kt i

C=Z (Z=O, N, S) v C-X (X=Cl, Br, I) tng ng vi bc chuyn electron n *. S

lin hp ny dn n s chuyn dch cc i v pha sng di nhng cng hp th thp.

CH2 = CH2 CH2 = CH CH =O -CH=O

max = 175 nm max = 345 nm (n - 3*) max = 305 nm (n -

*)

( - *) max = 218 nm ( - 3*) max = 175 nm ( -

*)

* *

1

4*

n

S kiu lin hp - p

3*

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Khi mch lin hp - tng ln th bc chuyn n * cng rt ngn, do cc

i hp th chuyn dch v pha sng di. Di hp th ny c k hiu l di R. Di R c

cc i hp th nm v pha sng di hn di K nhng cng hp th lun nh hn ( ~100). max nm trong vng 300-350nm.

- Lin hp - hay cn gi l siu lin hp

Nhm ankyl th lin kt gy ra hiu ng siu lin hp. Hiu ng ny lm cc i

hp th chuyn dch v pha sng di mt t nhng khng ln nh hai hiu ng trn, max

khng tng hoc tng khng ng k.

Chuyn dch bc sngmaxv pha sng di: lin hp p > lin hp >lin hp .

S tng cng hp th max: lin hp > lin hp p > lin hp .3.1.3. Phn loi di hp th

Trong ph electron c cc bc nhy electron t qu o c mc nng lng thp

sang qu o c mc nng lng cao nh *, *, n*, *. V tr ca cc nh

hp th tng ng vi cc bc nhy ny c mt s tnh cht c trng ring do ngi ta

phn chng thnh tng loi gi l cc di hp th nh di R, di K, di B v di E.- Di R: tng ng vi bc nhy electron n *. N xut hin cc hp cht c

cha cc d t vi cp electron t do nh O, N, S, v lin kt trong phn t. c trng

ca di R l hp th phn t thp, max thng nh hn 100. Mt khc, n lun lun cn

li trong ph khi c s thay i cu to phn t lm xut hin cc di khc sng ngn. Khi

di R chuyn dch cht t v pha sng di v c cng cao hn.

- Di K: xut hin quang ph ca cc phn t c h thng lin hp * nh

butadien hay mesityl oxit. N cng xut hin trong cc phn t ca hp cht vng thm c

lin hp vi cc nhm th cha lin kt nh styren, benzadehyt hay axetophenon. Di K

tng ng vi bc nhy electron * v c trng bi hp th cao, max > 10.000.

- Di B: c trng cho quang ph ca phn t hp cht vng thm v d vng.

Benzen c di hp th rng cha nhiu nh cu trc tinh vi, vng t ngoi gn gia 230

v 270 nm ( ~ 230). Khi c nhm mang mu ni vi nhn thm, di B quan st c

vng sng di hn di K nhng di K c cng hp th cao hn

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V d: stiren c di K max = 244 nm (max = 12.000) v di B max = 282 nm (max

= 450).

- Di E: ging di B l c trng ca cu trc vng thm. Ngn gc ca n l dobc chuyn electron h benzenoit ca ba lin kt etilen trong h thng lin hp vng kn.

Di E1 v E2 ca benzen tm thy gn 180 nm v 200nm. hp th phn t ca di E thay

i trong khong t 2.000 n 14.000.

3.1.4. Cc chuyn dch v hiu ng.

- Chuyn dch bathochrome (bathochrome shift): chuyn dch max v vng c bc

sng di.

- Chuyn dch hypsochrome (hypsochrome shift): chuyn dch max v vng c bcsng ngn.

- Hiu ng hyperchrome (hyperchrome effect): tng cng hp th max.

- Hiu ng hypochrome (hypochrome effect): gim cng hp th max.

3.1.5. Cc yu t nh hng n cc i hp th maxv cng hp th maxTrong ph UV, i lng c trng l max (max) v c xem xt cn c trn s lin

hp ca phn t.

1. Hiu ng nhm th

Khi thay th nguyn t H ca hp cht anken hay vng thm bng cc nhm th khc

nhau, ty theo nhm th c lin hp hay khng lin hp i vi h ni i ca phn t

m nh hng nhiu hay t n ph t ngoi ca phn t. i vi cc nhm th khng lin

hp (nh CH3, CH2OH, CH2COOH) th nh hng t cn cc nhm th lin hp (nh

C=CR2, COOH, OH, NO2 ) c nh hng mnh lm chuyn dch cc i hp th v pha

sng di v tng cng hp th.2. Hiu ng lp th

Khi tnh ng phng ca phn t b mt i th s lin hp ca phn t b ph v, lm

max gim i mt t nhng max gim nhiu, v vy c th xem max l cn c so snh tnh

ng phng ca mt dng phn t cho trc.

V d: Xt phn t biphenyl th orto: gi l gc to nn gia hai mt phng cha

hai nhn phenyl, nng lng lin hp ca phn t c tnh theo phng trnh:

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E = Emaxcos2; Emax l nng lng lin hp khi = 0.

(s nhm th) max (nm) max

0 45 > 45 (mt nhm CH3)

= 90 (hai nhm CH3)

248236

226

19 00010 000

800

Toluen 261 225

- V d: Cc ng phn cis v trans:

- max (trans) ln hn max (cis) mt t nhng max (trans) ln hn max (cis) mt nhiu.

- ng phn cis ca hp cht c mch lin hp di c kh nng xut hin thm mt

cc i hp th pha sng ngn hn.

V d: trans--caroten: 460 (148 000), cis--caroten: 340 (50 000), 460 (90 000).

3. nh hng ca dung mi

Ty theo bn cht phn cc ca dung mi v cht tan m ph t ngoi ca cht tan

thay i theo cc cch khc nhau. Khi tng phn cc ca dung mi th di K chuyn dch

v pha sng di cn di R (n*) li chuyn dch v pha sng ngn.

3.1.6. Nguyn l Franck-Condon

Mi bc chuyn e u km theo bc chuyn dao ng v cc bc chuyn ny u

tun theo quy lut ka chn gi l nguyn l Franck Condon v bc chuyn t trng thi

e ny sang mt trng thi e khc xy ra rt nhanh (10-16s) trong khi dao ng ca ht

nhn xy ra chm hn (10-12s) nn khong cch ht nhn hu nh khng thay i trong

khong thi gian ny.

Theo nguyn l Franck Condon th trong s kch thch e rt nhanh, bc chuyn

gia cc trng thi dao ng no khng lm thay i khong cch ht nhn s c xc sutln nht. C hai trng hp xy ra:

- Khi b kch thch e, khong cch cn bng gia cc nguyn t khng i (r = r0),

ng cong th nng trng thi e c bn v b kch thch e khng lch nhau i vi khong

cch r. Bc chuyn dao ng = 0 sang = 0 c xc sut ln nht, trong cu trc dao

n ca ph t ngoi c cng ln nht cn cc nh khc c cng nh hn. ng

ph c cu trc khng i xng. c trng l ph ca naphtalen

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- Khi b kch thch e, khong cch cn bng gia cc nguyn t ln ln (r > r0), ng

cong th nng trng thi e b kch thch b chuyn dch so vi trng thi c bn. Bc

chuyn dao ng = 0 sang = 0 khng phi c xc sut ln nht m ln trng thi daong cao c xc sut ln hn m bo cho khong cch cc nguyn t khng i. ng

ph c cu trc i xng. c trng l ph ca benzen.

3.2. Cu to ca ph k t ngoi kh kin

Ph t ngoi v kh kin c thit k o c vng ph t 200 1000 nm. N gm hai

loi: loi 1 chm tia o im v loi hai chm tia qut c vng ph. C hai loi ny u gm

cc b phn sau:

1. Ngn sng: dng n Tungsten halogen (o vng 350-1000nm) v n teri hayn hiro (o vng 200-350 nm).

2. B chn sng: dng knh lc hoc b n sc. B n sc dng lng knh ch to

bng thch anh hoc cch t (vch t 2000 3600 vch/mm).

3. Detect: ph bin dng t bo nhn quang, c nhay v bn cao. Mt s my

hin nay dng detect l dn diot gm 1024 diot cho c vng t ngoi v kh kin.

4. B phn c tn hiu: loi my o im thng c b phn c tn hiu l ng h

o in th hoc b phn hin s. My hai chm tia dng b phn t ghi hoc ghp ni vi

my vi tnh v my in.

S cu to ca ph k hai chm tia ca hng Perkin Elmer

3.3. ng dng ph t ngoi kh kin.

Phng php ph t ngoi v kh kin c ngha quan trng trong lnh vc phn tch

nh tnh, phn tch cu trc phn t v phn tch nh lng. Nguyn tt ca phng php

phn tch nh lng l da vo mi quan h gia mt quang v nng dung dch theo

nh lut Lambert Beer. u im ca phng php quang ph t ngoi v kh kin trong

phn tch nh lng l c nhy cao, c th pht hin c mt lng nh cht hu c

hoc ion v c trong dung dch, sai s tng i nh (ch 1 n 3%)

Ngoi ra, n cng cn c s dng xc nh hng s cn bng, hng s phn li v

nghin cu ng.

3.3.1. Phng php o mt bc sng

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phn tch mt mu c th thc hin theo cch n gin l o mt mu chun v

m mu phn tch ri tnh ton theo cng thc di y. Gi nng ca cht chun l Ck,

ca mu phn tch l Cx, da theo nh lut Lambert Beer c th vit:Dk= kCkdk hay k= Dk/Ckdk

Dx = xCxdx hay x = Dx/Cxdx

vi: Dk, Dx l mt quang ca dung dch mu chun v mu phn tch.

dk, dx l chiu dy lp mng ca dung dch mu chun v mu phn tch.

k, x l h s hp th mol.

Ck, Cx l nng ca dung dch mu chun v mu phn tch.

T hai phng trnh trn suy ra:xk

kkxx dD

dCDC

Nu chn cuvet o mu chun v mu phn tch c chiu dy nh nhau tc l dk = dx

th c th vit:k

kxx D

CDC

Ck l nng mu chun c pha chnh xc, Dkv Dx l gi tr o c trn my do

tnh c nng mu phn tch.

3.3.2. Phng php lp ng chun1. Chn max

2. Pha dy cht chun c nng tng (gim) dn.

3. o mt quang ca cc mu bc sng trn.

4. V th ph thuc mt quang D vo nng C, ng biu din ca th

ny c gi l ng chun.

5. Pha mu phn tch sao cho nng dung dch mu o nm trong gii hn tuyn

tnh ca ng chun. Sau khi o mu phn tch nhn gi tr Dx ri i chiu trn th c

c gi tr Cx.

3.4. Phn gii ph UV-VIS

3.4.1. Dng ph U-VIS

D(), D(), D(lg);

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3.4.2. Phn gii ph UV-VIS

Ph t ngoi ca -carotene trong dungmi n-hexan, etanol

Ph t ngoi ca metyl propinyl xeton

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Da vo max , c th bit c loi lin kt

- max < 150nm: ch c loi lin kt ca hp cht no.- max > 150 nm: c lin kt bi- max quanh vng 200 260 nm c th c benzen v benzen th.- max >280 nm: h lin hpmax cng ln th h lin hp cng di.

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CHNG 4. PH CNG HNG T HT NHN (NMR)

Ph cng hng t ht nhn (ph CHTHN) vit tt ca ting Anh l NMR (nuclear

Magnetic Resonance) l mt phng php vt l hin i nghin cu cu to ca cc hpcht hu c, n c ngha quan trng xc nh cu to cc phn t phc tp nh cc hp

cht thin nhin. Phng php ph bin c s dng l CHTHN-1H v ph CHTHN-13C.

4.1. C s vt l hc

4.1.1. Ht nhn trong t trng

- Ht nhn ca mi ng v ca mt nguyn t c c trng bi s lng t spin I

v s lng t t m.

I: s lng t ca spin ht nhn (I = 0, , 1, 3/2, 5/2 )mI: s lng t t ht nhn mI = (2I+1) c cc gi tr khc nhau l -I, -I + 1, cho n

+I.

- Thc nghim: mi ht nhn nguyn t c mt s lng t spin I ht nhn nht nh,

ph thuc vo s khi ca nguyn t A v s th t ca nguyn t l Z:

S khi A l chn chn

S th t Z Chn/l Chn l

S lng t t spin , 3/2, 5/2 0 1, 3, 5

Cc ht nhn ca nguyn t tch in dng, lun lun t quay quanh trc ca n, khi

quay nh vy, n sinh ra mt mmen qun tnh gi l momen spin ht nhn P v momen t

. Mt khc, khi ht nhn nguyn t quay quanh trc ca n th in tch ht nhn s chuyn

ng trn mt vng trn quanh trc quay, lm xut hin mt dng in. Mi mt dng in

bao gi cng km theo mt t trng nn khi ht nhn quay cng xut hin mt t trng c

mmen t v ht nhn tr thnh mt nam chm vnh cu. Mmen spin ht nhn P t l

thun vi momen t :

P. (1)

: h s t thm c trng cho mi ht nhn nguyn t.

Gi tr tuyt i ca momen spin ht nhn P tnh theo I:

P = (h/2).I (2)

Gi tr tuyt i ca momen t tnh theo I:

= (h/2).I (3)

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I: s lng t spin ht nhn.

I = 0 th = P = 0

I 0 th 0 v P 0: ht nhn c gi l ht nhn t.y l iu kin c cnghng t.

Bng 1. Nhng ht nhn thng gp trong hp cht hu c

ng v % trong t nhin s proton s ntron I nhy tng i

H1 99,98 1 0 2,793 1,000

D2 1,56.10- 1 1 1 0,857 9,64.10-

C12 98,89 6 6 0

C13 1,108 6 7 0.702 1,59.10-

N14 99,635 7 7 0 0.404 1,01.10-3

N15 0.365 7 8 5/2 -0,283 1,04.10-

O16 99,96 8 8 3/2

O17 3,7.10-2 8 9 3/2 -1,893 2,91. 10-2

Cl35 75,4 17 18 3/2 0.821 4,71.10-3

Cl

37

24,6 17 20 3/2 0.683 2,72.10-3

Br79 50,57 35 44 3/2 2,099 7,86.10-2

Br81 49,43 35 46 3/2 2,263 9,84.10-

F19 100 19 0 0,833

P31 100 31 0 6,6310-

Ph cng hng t ht nhn ph thuc vo % ng v v momen t . Khi cng ln

th nhy cng cao.4.1.2. S tch mc nng lng ca ht nhn trong t trng ngoi

1. Kim nam chm nhn bt k nng lng no ca t trng ngoi

Mt kim nam chm trong t trng ca tri t th kim nam chm s hng theo t

trng ca tri t. Nu lm lch kim nam chm mt gc ri th kim nam chm t do th

n s chuyn ng tr li v tr cn bng ban u. V tr cn bng l v tr c mc nng lng

thp nht. Gc lch cng cao th nng lng E ca kim nam chm cng ln:

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00.BE (4)

cos.BE 0 (4)

Cos = (-1,+1) nn E = (+B0, -B0) c gi tr lin tc.E: nng lng ca kim nam chm; B0: cng ca t trng ngoi.

: gi tr tuyt i momen t ca nam chm.

: gc lch

2. Ht nhn t khc vi kim nam chm, ch nhn nng lng gin on (lng t ho)

Khi khng trong t trng, cc ht nhn c cng u mc nng lng bng

nhau. Khi t mt ht nhn t vo trong mt t trng ngoi c cng B0 th cc momen

t ca ht nhn t s xoay theo hng c ng sc t ca t trng ngoi.

Ht nhn nguyn t t khi trong mt t trng ngoi khc vi mt kim nam chm

trong t trng ca tri t: ht nhn t khng phi tip nhn bt k mt v tr no ca t

trng bn ngoi m n ch mt s v tr nht nh trong khng gian tng ng vi mt s

trng thi nn lng xc nh ngha l nng lng ca ht nhn t c th hin qua gi tr

ca cos: cos = m/I (5)

I: s lng t ca spin ht nhn (I = 0, , 1, 3/2, 5/2)

mI: s lng t t ht nhn (m = -I n +I) c 2I + 1 gi tr

V d 1: Ht nhn 1H, 13C, 31P; c I =

Khi I = th mI = - v v mI c 2.1/2 + 1 = 2 gi tr

T (5) suy ra cos = -1 v +1 nn = 0 v =

V d 2: Ht nhn 2D, 14N; I = 1

Khi I = 1 th mI = -1,0,+1 c 2.1+1 = 3 gi tr

T (5) suy ra cos = -1,0,1 nn = /4; = 0 v = 3/43. S tch mc nng lng ca ht nhn trong t trng ngoi

Cc ht nhn nguyn t 1H, 13C, 31P c s lng t spin ht nhn I = v s lng

t t mI = - v , khi t chng vo trong t trng ca nam chm th cc spin ny s

quay hng ngc chiu nhau v chim hai mc nng lng khc nhau c hiu s l:

00 B2

1hayB

2

h.hE

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y:I

2

hI

m..Bcos..BE 00

Do : 0B.m.2h

E

Khi m = : 01 B..2h

2/1E

m = -: 02 B..2h

2/1E

Vy: 00 B..21

hayB..2

h.hE

y, E l nng lng cng hng, l tn s cng hng, B0 l cng ca t

trng nam chm, l h s t thm, mi ht nhn c gi tr khc nhau nh (1H) ~ 4(13C).

Hnh v sau ch ra s phn tch mc nng lng ca ht nhn t t trong t

trng ngoi, ht nhn c s lng t t m = c mc nng lng thp cn ht nhn t c

s lng t t m = - c mc nng lng cao, hiu s gia hai mc nng lng l E.

S phn b ny khng bng nhau, s ht nhn nng lng thp bao gi cng nhiu

hn s ht nhn nm mc nng lng cao mt t v tun theo s phn b Boltzman:

1eN

NkT

E

1

2

N1: s ht nhn chim mc nng lng thp

N2: s ht nhn chim mc nng lng cao

E m = -1/2

m = 1/2

E = (h/2)B0vng t trng

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T: nhit tuyt i

4. iu kin kch thch ht nhn t ( tch mc nng lng trong t trng B0)

Mun xy ra hin tng cng hng phi chiu vo ht nhn mt t trng B 1 c tns cng hng l 1 sao cho B1 vung gc vi B0.

Khi : 0101 B..21

B..2

hEh

1 l tn s cng hng t (tng ng vi nng lng cn kch thch ht nhn chuyn

t mc thp ln mc cao nm trong vng sng v tuyn 108 106 Hz

4.1.3. Hin tng cng hng t ht nhn

Khi cho mt t trng B0 tc dng ln cc phn t c cha ht nhn th s dn ti s

tch mc nng lng v dn n s phn b cc ht nhn theo cn bng Boltzmann.

Trong t trng B0, cc ht nhn khng nm yn m trng thi cn bng ng. Nu

mun ph v trng thi cn bng ng ny cn phi cung cp nng lng t ngoi vo bng

cch cho mt t trng khc c cng B1 tc dng vo cc phn t ny. iu s lm

thay i li s phn b cc ht nhn gia hai mc nng lng trn. Mt s ht nhn s hp

th nng lng ca t trng B1 nhy t mc nng lng thp ln mc nng lng cao

v ngc li, mt s ht nhn mc nng lng cao s bc x nng lng chuyn xungmc nng lng hp. Nng lng cn thit cung cp cho qu trnh thay i ng bng

E = nng lng cng hng t nhn. Qu trnh hp th nng lng E phn b li cn

bng ngj trong t trng B1 gi l hin tng cng hng t nhn. Hin tng cng

hng t xy ra khi ht nhn hp th cc nng lng c tn s bng 0 c gi l tn s

cng hng t.

4.2. chuyn dch ho hc

4.2.1. Hng s chn v t trng hiu dngHng s chn xut hin do hai nguyn nhn:

- Hiu ng nghch t: cc in t bao quanh nguyn t sinh ra mt t trng ring,

ngc chiu vi t trng ngoi nn lm gim tc dng ca n ln ht nhn nguyn t. Lp

v in t cng dy c th t trng ring ngc chiu vi t trng ngoi cng ln tc

hng s chn cng ln.

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S hiu ng nghch t

V vy, cc proton nm trong cc nhm c nguyn t hay nhm nguyn t gy hiu

ng I (Cl, Br, I, NO2) s c hng s chn nh, tri li khi cc nhm nguyn t gy hiung +I (CH3, C2H5) s c hng s chn ln.

- Hiu ng thun t: bao quanh phn t l lp v in t, cc in t ny chuyn

ng sinh ra mt dng in vng, do xut din mt t trng ring c hng thay i

ngc hng hoc cng hng vi t trng ngoi. Tp hp tt c cc im trn cc ng

sc m ti tip tuyn vung gc vi t trng ngoi s to nn mt mt parabon. Pha

trong mt parabon, t trng tng hp nh hn B0 v t trng ring ngc hng vi t

trng ngoi, cn pha ngoi parabon th t trng tng hp ln hn B0 v t trng ringcng hng vi t trng ngoi. Do hng s chn pha ngoi parabon nh cn pha trong

th c hng s chn ln ngha l chuyn dch hc cng cc proton nm pha ngoi

parabon s ln cn pha trong s nh.

S hiu ng thun t : a) benzen; b) nhm C=C; c) nhm C=O; d) nhm CC

Khi t mt ht nhn nguyn t vo mt t trng ngoi B0 th cc e quay quanh ht

nhn cng sinh ra mt t trng ring B c cng ngc hng v t l vi t trng

ngoi:

B = -B0

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T trng thc tc dng ln ht nhn l:

Be = B0 B = B0 B0

Be = B0 (1-)Be l t trng hiu dng

: l hng s chn c gi tr khc nhau i vi mi ht nhn nguyn t trong phn t.

Ph thuc vo s e, nu s e cng nhiu th cng ln.

Hng s chn t l thun vi in tch e, mt e bao quanh ht nhn v t l nghch

vi khi lng e. Hng s chn cng ln th t trng hiu dng Be cng nh.

4.2.2. chuyn dch ho hc

i vi cc ht nhn trong phn t cng phc tp trong nguyn t do nh hng cacc m my electron ca cc nguyn t bn cnh.

V d: xt 1H nhm CH3 ca phn t TMS (CH3)4Si v1H nhm CH3 ca axeton:

Do nh hng ca nhm CO ht e lm cho m my electron 1H ca axeton < 1H

ca TMS nn: 1H (TMS) > 1H (aceton)

Be (TMS) < Be (aceton) ti v tr ht nhn1H trong TMS so vi trong

aceton.

Do hiu ng chn t khc nhau nn cc ht nhn 1H v 13C trong phn t c tn scng hng khc nhau. c trng cho cc ht nhn 1H v 13C trong phn t l gi tr

chuyn dch ho hc .

Vi cng mt t trng ngoi B1, c tn hiu cng hng ca1Hvi t trng, tn

s cng hng (aceton) > TMS hoc t trng s dng i vi TMS phi c cng ln

hn i vi aceton. C hai phng php to ra iu kin tho mn iu kin cng hng

(1=(1/2)..B0) ghi tn hiu cng hng.

1. Phng php qut trng: thay i B0

t TMS v aceton vo t trng B0 v s dng mt t trng b sung, tng dn

cng ca t trng b sung n mt lc no cng t trng hiu dng tc

ng ln xut hin tn hiu cng hng. V Be(TMS) < Be (aceton) nn ch cn b sung mt

gi tr t trng B0 Be nh hn th aceton xut hin tn hiu cng hng trong khi

th t trng tc dng ln v tr ht nhn 1H (TMS) cha mnh cha c tn hiu cng

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hng. Tip tc tng t trng b sung n mt gi tr no t trng tc dng ln1H(TMS) t bng B0 th xut hin tn hiu cng hng ca

1H (TMS).

Ph1

H-NMR ca hn hp axeton-TMSKhong cch gia hai tn hiu ca TMS v aceton l:

0acetonTMS0aceton00TMS0 B)()BB()BB(B

Khong cch ny va ph thuc vo hng s chn va ph thuc vo cng t

trng ngoi B0.

acetonTMS0B

B

Ch ph thuc vo hng s chn, khng ph thuc vo t trng ca thit b.2. Phng php qut tn

Gi nguyn t trng B0, thay i tn s ca t trng B1 c s cng hng

aceton > TMS.

- Khi t hai ht nhn nguyn t 1H ca cng nguyn t hydro ca TMS v ca

aceton vo mt t trng ngoi B1, khi c cng hng th:

aceton0aceton

TMS0TMS

1B..21

1B..2

1

Hiu s: )(B..2

1acetonTMS0acetonTMS

acetonTMS1

Vi k thut o ny cng c th ghi nhn c l i lng khng ph thuc vo

thit b bn ngoi.

axetonTMS (xut hin mun nht

1H (axeton)

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Nh vy, d thay i cng t trng ngoi B1 hay thay i tn s sng radio u

c th biu din theo l i lng khng ph thuc vo thit b bn ngoi. Trong k thut

o, ngi ta khng th o c gi tr tuyt i ca TMS, aceton v nhng c th o ckhong cch gia hai tn hiu proton , thay i tu theo ln ca t trng B1 nhng

khng thay i.

TMS l cht c hng s chn ln nht nn dng n lm cht chun o chuyn

dch ho hc.i vi ht nhn 1H th:

0

TMSHHTMS

y, TMS

l hng s chn ca cht chun TMS (tetrametylsilan), H

l hng schn ca ht nhn mu o, TMS H l tn s cng hng ca cht chun v ca ht nhn mu

o. Hng s chn xut hin do nh hng ca m my electron bao quanh ht nhn

nguyn t, do tu thuc vo v tr ca ht nhn 1H v 13C trong phn t khc nhau m mt

electron bao quanh n khc nhau dn n chng c gi tr hng s chn khc nhau v

do chuyn dch ho hc ca mi ht nhn khc nhau.

Tng qut: = TMS X

X: hng s chn ca cht cn o. khng c th nguyn m c tnh bng phn triu (ppm).

i vi ph CHTHN 1H th c gi tr t 1 n 12 ppm cn ph 13C th c gi tr t

0 n 220ppm.

Vy chuyn dch ho hc l i lgn c trng cho nhng ht nhn cng loi

ca mt n v b che chn tng ng nhau trong mt hp cht. N khng ph thuc vo

thit b bn ngoi (cng t trng hay tn s sng) khng c th nguyn v c tnh

bng ppm.

V d:

+ Phn t C6H5-CO-CH3, ph CHTHN1H c:

CDHH = 7,5-8,2ppm ca C6H5

= 2,5ppm ca CH3

+ Phn t CH2=CH-COO-CH2CH3, ph CHTHN1H c:

CDHH = 6,2 ppm ca =CH2 v 5,8 ppm ca =CH

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= 4,2 ppm ca CH2- v 1,2 ppm ca CH3

Thang CDHH

Da vo chuyn dch ho hc c th xc nh c cu to ca phn t.

V d: phn t CH3CH2OH s cho 03 tn hiu c trng cho mi nhm:

4.3. Tng tc spin spin

Phn t etanol CH3CH2OH l ra trong ph CHTHN-1H ch c 3 tn hiu ng vi 03

nhm CH3, CH2 v OH nhng trn ph thc nghim xut hin bi nh mi nhm: CH3 l

03 nh, CH2 l 04 nh v OH l 03 nh (vi etanol khan tuyt i) hoc 1 nh (etanolthng) nh hnh v di:

3,7 2,5 1,2 0 , ppm

HO CH2 CH3

3,7 2,5 1,2 0 , ppm

HO CH2 CH3

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Ph cng hng t ht nhn ca 1H ca etanol

Nguyn nhn ca s xut hin bi nh ny l do s tng tc ca cc proton nm

cnh nhau. Mi proton ging nh mt nam chm nh, n sinh ra hai t trng ph ngc

chiu nhau tc dng ln proton bn cnh lm phn tch mc nng lng ca t trng

ngoi B0 tc dng ln proton , kt qu sinh ra tn hiu bi, s phn tch mc nng lng

th no tu thuc vo s proton mi nhm. Hin tng ny c gi l tng tc spin

spin.

hiu r vn ny, c th kho st mt v d c th l s tng tc ca cc proton

trong phn t 1,1,2-tricloetan di y trong cc proton c k hiu l Ha, Hb, Hc.

Trc tin, c th coi Ha l mt nam chm nh, n sinh ra hai t trng ph ngc

chiu nhau. T trng ph ny tc dng ln vng quanh ht nhn Hb v Hc c th qua khng

gian hoc e lin kt, phn tc dng qua khng gian gi l tng tc trc tip nhng i vi

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cht kh v lng n xy ra rt nhanh khng o c, phn tc dng qua e xy ra chm hn c

th pht hin c gi l tng tc khng trc tip. i vi cht rn c th o c tng

tc spin spin qua khng gian, kt qua cho mt tn hiu rng. y, ht nhn Ha tc dng ln ht nhn Hb v Hc 2 t trng ph ngc chiu nhau,

lm phn tch mc nng lng ca t trng ngoi tc ng ln Hb v Hc thnh 2 mc do

cho hai tn hiu ph. V Hb v Hc c ci l tng ng nn 2 tn hiu ph ny l ca c

Hb v Hc.

Ngc li, Hb v Hc cng tc ng ln Ha bng hai t trng ph ngc chiu nhau,

t hp li ta s c cc hnh khc nhau nh hnh di:

Hb B0 Hc

Nhn s trn thy c ba trng hp khc nhau: th nht Hb v Hc tc ng ln Ha

ngc chiu nhau, trng hp th 3 c Hb v Hc tc ng ln Ha hai t trng ph ngc

chiu nhau vi t trng ngoi Bo. Kt qu l mc nng lng B0 tc ng ln Ha phn tch

lm ba mc v do cho ba tn hiu ph khc nhau nh hnh v trn ng vi nhm Cl2CH-

nhn c ba nh cn i vi nhm ClCH2- nhn c 2 nh.

bi ca tn hiu (s nh trong mi nhm) ph thuc vo s proton nhm bn cnhm n tng tc.

bi M = N + 1 (N-s ca nhng ht nhn t tng ng bn cnh)

V d: bi ca cc nhm nh sau:

1) 1,1,2-Tricloetan: Cl2CH-CH2Cl

CHCl2: 2+1 = 3 nh 1+1 = 2 nh : CH2Cl

Nhm CH c 3 nh cn nhm CH2c 2 nh

2) Etanol: HO CH2 CH3

CH3: 3 + 1 = 4 nh 2 + 1 = 3 nh

Nhm CH2 c 4 nh cn nhm CH3 c 3 nh

3) 2 Clopropan Cl-CH(CH3)2

CH: 6 + 1 = 7 nh 1 + 1 = 2 nh: CH3

Nhm CH c 7 nh cn 2 nhm CH3 c hai nh v 2 nhm CH3 tng ng coi

nh c 6H nh nhau.

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T l cng tn hiu ca mi nhm tun theo tam gic Pascal nh sau:

T l chiu cao cc vch trong mi nhm S nh K hiu S proton (N)

1 1 nh Singlet 01:1 2 nh duplet 1

1:2:1 3 nh Triplet 2

1:3:3:1 4 nh Qualet 3

1:4:6:4:1 5 nh Quynlet 4

1:5:10:10:5:1 6 nh Sexlet 5

1:6:15:20:15:6:1 7 nh septet 6

Nhn s trn thy cc nhm tn hiu c bi ln th cng tn hiu nh gia

v nh ngoi gp nhau nhiu ln v th i vi nhm 6, 7 nh tr ln th ch xut hin mt

s t hn. V d nhm 7 nh thng ch xut hin 5 nh.

Ngoi ra khong cch gia hai nh lin nhau mi nhm c o bng Hertz (Hz)

v c gi l hng s tng tc spin-spin J. y l mt thng s ph quan trng nh

chuyn dch ho hc.

4.4. ng cong tch phn tn hiu

Din tch gii hn bi ng cong ph t l vi s proton ca mi nhm nhng do

vic o din tch ny kh chnh xc nn ngi ta s dng ng cong tch phn xc nh

t l s proton ca mi nhm, v chiu cao ca bc thang t l vi s proton mi nhm.

Ngoi ra, chiu cao bc thang cn t l vi nng cht trong dung dch, do ngi ta c

th tnh c nng cht da vo ng chun v cht chun.

V d, phn t toluen C6H5 cho hai nhm tn hiu ng vi phn phenyl (cha 5H) v

vi nhm metyl (cha 3H) th din tch ny s l:

S (C6H5) : S (CH3) = 5:3

S: din tch ca mi tn hiu

Tuy nhin vic tnh ton din tch ny thng kh khn do s xut hin a vch

mi nhm. khc phc tr ngi ny, ngi ta s dng k thut tch phn tn hiu, v cc

ng cong bc thang. Chiu cao ca cc bc thang trn mi nhm tn hiu cng hng

cng t l vi s proton ca mi nhm. ng cong ny c gi l ng cong tch phn.

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Ph cng hng t ht nhn proton ca etylbenzen. Chiu cao bc thang ng cong tch

phn t l vi s proton moix nhm

4.5. Phng php phn tch ph cng hng t ht nhn 1H

Nhim v ca phn tch ph cng hng t ht nhn l phi tm c cc thng s t

cc ph ghi ra. y, gii hn vic tm cc gi tr: chuyn dch ho hc v hng s

tng tc spin spin (J) ca cc proton v cc ht nhn khc c I = .

4.5.1. K hiu ca ph

Khi gia hai hay nhiu ht nhn trong phn t c tng tc spin spin vi nhaungi ta ni n h ht nhn. Ngi ta k hiu cc ht nhn bng cc ch ci A, B, C, ,

M,X, Y...

Cc ht nhn ca cng loi ht nhn v c chuyn dch ho hc nh nhau gi l

cc ht nhn tng ng v c k hiu bng mt loi ch ci, cn s lng cc ht nhn

ny c ghi bng ch s pha di bn phi v d: A2B, A2X S nh gi cc ph ph

thuc vo t l ca hiu s chuyn dch ho hc v hng s tng tc spin:

KJJ 1212

21

Nu hiu s ca chuyn dch ho hc ca hai nhm ht nhn nh hn hng s

tng tc ca chng (K < 1) th ngi biu din nhng ht nhn ny bng cc ch ci lin

tip nhau. V d: AB, A2B, ABC.

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Ngc li, nu hiu s ca chuyn dch ho hc ln hn hng s tng tc ca

chng th ngi ta biu din h ht nhn bng ch ci cch xa nhau; v d: AX, A 2X,

AMX,Trng hp K > 6 th xp vo ph bc 1. Cn li xp vo ph bc cao.

4.5.2. Ph bc 1

i vi ph bc 1, c th p dng quy tt s vch ti v t l chiu cao cc nh

trong mt nhm tun theo quy tt Pascan.

H ph bc 1 thng c dn AmXn v AmMnXy. Cc h ph AX c h tm thy s

nh ca mi nhm d dng v hng s tng tc J v tn s A hay X.

V d:

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4321ABJ

V d: ph cng hng t ht nhn ca 3-brom-2-tert-butoxithiophen

2. Ph A2B

ph l thuyt ca A2B

Ph A2B l h gm 3 ht nhn tng tc vi nhau trong c hai ht nhn tng

ng. Ph gm hai phn, v l thuyt phn A v 8 nh v phn B c 6 inh (hnh v)

nhng ph thc th s nh t hn. V d, ph 1H-NMR ca 1,3,4 tribrombut-1-in phn A

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ch xut hin 4 nh v phn B 4 nh (hnh v). C th phn tch ph A2B nh trn hnh v,

tnh cc gi tr nh sau:

8,54,1AB

75A3B

3

1J

21;

Ph1H-NMR ca 1,3,4-tribrombutin-1

3. Ph ABXPh ABX thng gp trong p cng hng proton c bit cc hp cht thm v

anken cng nh cc hp cht cha ht nhn t khc (19F, 31P) gm ba ht nhn khng tng

ng tng tc vi nhau phn tch ph thnh hai phn ring bit. phn tch ph cn

tch ring bit phn AB v phn X, v d ph 1H-NMR ca stirenoxit di, phn AB c 8

nh v phn X c 4 nh.

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V l thuyt, h ph ABX gm hai phn, phn AB c 8 nh cn phn X c 6 nh,

thc hin ta tm chia phn AB thnh AB v AB, t phn ny c th tm c J AB v cc

gi tr:

BXB,,BXAA

,,A

BXB,BXAA

,A

J21

;J21

J2

1;J

2

1

Tu theo s cng du hay tri du ca JAX v JBX m dng ph thay i nh sau:

Trong phn AB c hai nhm 4 nh, t y tm c A, B, JAB, JAX, v JBX, trongphn X ch tm c X.

4.5. Phn tch ph cng hng t ht nhn 13C

V tt c cc hp cht hu c u cha nguyn t cacbon m tron nhin nguyn t

cacbon -13 chim t l 1,1% nn ph cng hng t nhn 13 C (CHTN- 13 C) hin nay c

ngha quan trng, n cho nhiu thng tin hn ph CHTN- 1H, v d hp cht hu c

khmg cha hiro th khng c tn hiu trong ph CHTN- 1H nhng n cho tn hiu ca ph

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CHTN- 13 C. V t l ca 13 C nh v hng s t l gyromagnetic thp nn tn hiu cng

hng t thng nh, ngi ta phi o trn ph k cng hng t bin i Fourier (FT). Khi

dng my ny c th ghi ph CHTN-13

C theo mt s cch khc nhau, nhng quan trng nhtl phng php ph 13 C tng tc 1H v xo tng tc 1H. C hai phng php u cho cc

thng tin gi tr trong vic phn tch cu trc cc hp cht hu c.

4.5.1. Ph 13 C tong tc 1H

Trn ph tng tc 13 C - 1H nhn c cc nhm nh khc nhau c th nh n

hay bi nh. V 13 C v 1H u c I= nn quy tc a vch c p dng ging nh tng

tc 1H - 1H Ca ph CHTN- 1H :

siglet (1 vch) khng c C

duplet (2 vch) c 1 CH

triplet (3 vch) c 2 H CH 2

quartet (4 vch) c 3 H CH 3

Hng s tng tc J( 13 C-H) ph thuc vo c trng s ca obitan lai ho nguyn t

cacbon.c trng s cng ln th hng s tng tc cng ln:

Lai ho JC-H (Hz)

CH sp3 125

CH sp2 160

CH sp 250

Khi c nhm th m in gn vo nguyn t cacbon th 1J HC thng tng:

CH 4 125 H Z , CH 3 Cl 151 H Z , CH 2 Cl 2 178 H Z , CHCl 3 209 H Z

Tng tc C v H cch xa nhau hn 1lin kt thng rt nh, v d 2 J HC = 5 H Z ,

thng khng thy.

Tng tc gia 13 C v 13 C cnh nhau t c ngha cho vic chng minh cu to.

4.5.2. Phng php ph 13 C xo tng tc 1H

Ph 13 C tng tc 1H cho nhiu nhm nh do s khc nhau v s proton trong cc

nhm CH, CH 2 v CH 3 , nhng cng ca cc nh qu nh ln vi c nhiu ca my,

do vic gii ph gp kh khn, v vy ngi ta a ra cch lm n gin ho bn ph

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chn mt s hng tin cn thit, bng cch xo i cc vch tng tc C-H. By gi ng vi

mi nguyn t cacbon ch co 1 vch ph. V d:

Ph CHN-13C c tng tc(a) v xo tng tc C-H (b)

Trong tp ch, loi ph CHTN- 13 C xo tng tc C-H c k hiu l 13 C H1 .

Thc t ph CHTN- 13 C tng tc C H ngy nay t o. Thay cho phng php , ngi

ta dng cc phng php k thut hin i nh APT.(Attached Proton Test) c th phn bit

c C, CH, CH 2 v CH 3 .

Khi dng k thut ny th tn hiu ca nhm C v CH 2 nm pha trn, cn tn hiu

ca nhm CH v CH 3 nm pha di ng nm ngang nh hnh 4.18.

Ngoi ra cn s dng phng php DEPT ghi ph, theo phng php ny tn hiu

CH 3 v CH pha trn cn CH 2 pha di. V d ph CHTN-13 C ghi theo DEPT ca 2-

butanol di:

Cng vch ph ton ph xo tng tc 13 C- 1H t l vi:

1- S nguyn t hiro gn vi nguyn t cacbon.2- S nguyn t cacbon tng ng.Thng th nhm CH 3 v CH 2 cho cng vch ph nh nhau, nhng nhm CH

v C cho cng yu hn. V d:

CH3-CH2CH(OH)-CH3CH

CH2

CH3 CH3

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4.5.3. chuyn dch ho hc

V tr ca cc tn hiu cng hng 13 C rt quan trng cho vic xc nh cu to cc

hp cht. chuyn dch ho hc 13 C nm trong mt vng rng hn nhiu so vi phCHTN- 1H, t 0 n 200 ppm. hin nay cht chun thng dng l TMS, dung mi ghi ph

thng dng l cc cht d 6 -axeton, d 6 -benzen, d 1-clorofom, d 12 -xiclohexan, d 6 -

dimetylsunfoxit, d 4 -metanol, tetraclometan

chuyn dch ho hc 13 C c xc nh bi:

a) Mc lai ho ca nguyn t cacbon.b) m in cua cc nhm th nguyn t cacbon.Cc nhm th c nh hng mnh n s thay i v tr chuyn dch ho hc, v

d:

CH 3 l CH 3 Br CH 3 Cl CH 3 F

-33 9 24 75 ppm

R-C(CH3)3CH3

3xCH3

C 1

2

3

4

1

2

4

3

R-C6H11 R-C6H5

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CHNG 5

PH KHI CA CC HP CHT HU C

Phng php ph khi lng c ngha rt quan trng i vi vic nghin cu xcnh cu trc cc hp cht hu c. Da trn cc s khi thu c trn ph c th xy dng

cu trc phn t hoc chng minh s ng n ca cng thc cu to d kin.

5.1. Qu trnh ion ho phn t

5.1.1. S ion ho

Nguyn tt chung ca phng php ph khi lng l ph v phn t trung ho thnh

ion phn t v cc ion dng mnh c s khi z = m/e (m l khi lng cn e l in tch

ion). Sau phn tch cc ion ny theo s khi v ghi nhn thu c ph khi lng. Davo ph khi ny c th xc nh phn t khi v cu to phn t ca cht nghin cu.

Khi bn ph cc phn t hp cht hu c trung ho bng cc phn t mang nng

lng cao s tr thnh cc ion phn t mang in tch dng hoc ph v thnh mnh ion v

cc gc theo s sau:

ABCD + e ABCD+ + 2e

ABCD++ + 3e

ABCD-S hnh thnh cc ion mang in tch +1 chim 95%, cn li cc ion mang in tch

+2 hoc ion m (-). Nng lng bn ph cc phn t thnh ion phn t khong 10eV. Nhng

vi nng lng cao th ion phn t c th ph v thnh cc mnh ion dng (+), hoc ion

gc, cc gc hoc phn t trung ho nh hn:

ABCD+ + e ABC. + D+

AB. + CD+

A+ + BCD

A + BCD+

.

S ph v ny ph thuc vo cu to cht, phng php bn ph v nng lng bn

ph. Qu trnh ny l qu trnh ion ho.

Cc ion dng hnh thnh u c khi lng m v in tch e, t s m/e c gi l

s khi z. Bng cch no , tch cc ion c s khi khc nhau ra khi nhau v xc nh

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c xc sut c mt ca chng ri v th biu din mi lin quan gia cc xc sut c

mt (hay cng I) v s khi z th th ny c gi l ph khi lng.

5.1.2. Phn loi cc ion1. Ion phn t

Ion phn t c hnh thnh do mt i 1 electron, cho nn khi lng ca n chnh l

khi lng ca phn t hay trng lng phn t, c k hiu l M +. Ion phn t c cc tnh

cht sau:

- M+ l ion c khi lng ln nht chnh l trng lng phn t

- M+ l ion vi th xut hin nh nht.

- M+

l s chn nu phn t khng cha d t N hay cha mt s chn d t N v M+

s l s l nu cha mt s l d t N.

- Tt c s ph v phn t u c th tnh t hiu s khi lng ca cc phn t ion

vi ion phn t.

- Cng ca M+ t l vi p sut mu. N ph thuc vo dy hp cht, nng lng

ca electron v kh nng ph v phn t. Cng ca M+ c gi tr t 0 n 100%.

2. Ion ng v

Ion phn t ca cc hp cht khng phi ch l vch ring l v cc nguyn t chatrong hp cht thin nhin u tn ti ng v nh 13C bn cnh 12C, 15N bn cnh 14N, 17O,18O bn cnh 16O, 37Cl bn cnh 35Cl.

Cc ng v tn ti trong t nhin vi cc t l khc nhau cho nn bn cnh vch

chnh ng vi ion M+ cn c cc vch (M+1)+ v (M+2)+ vi cng nh hn. Chiu

cao ca cc vch ph ny t l vi s c mt ca cc ng v trong phn t. Ngi ta da

vo cc c im ny tnh cng thc cng ca cc hp cht nh phng php khi ph.

Chng hn, nguyn t cacbon trong thin nhin tn ti 12C 100%, 13C l 1,1%. Nh

vy, nu mt hp cht ch cha mt nguyn t cacbon nh metan th ion M+ c chiu cao

100% (12CH4) th ion (M+1)+ s c t l 1,1% (13CH4). phn t etan c hai nguyn t

cacbon nn ion M+ c chiu cao l 100% (12C2H6) th ion (M+1)+ s c chiu cao 2.1,1% =

2,2% (13CH312CH3). Nh vy, nu phn t c n nguyn t cacbon th ion (M+1)

+ s c t l

n.1,1% so vi chiu cao ca ion phn t M+.

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h.0011,0

hn

'

h l chiu cao vch ph M+ v h l chiu cao vch ph (M+1)+.

Khi bit c chiu cao ca cc vch ph c th tnh c s nguyn t cacbon trong

phn t.

Khi lng v thng gp trung bnh ca cc ng v trong mt s nguyn t:

ng v Khi lng thng gp tng i1H 1,0078 1002H 2,0141 0,015

C

12,0000 100C 13,0034 1,12

14N 14,0031 100

N 15,0001 0,36616O 15,9949 10017O 16,9991 0,037

O 17,9992 0,240

F 18,9984 100

Si 27,9769 10029Si 28,9765 5,11030Si 29,9738 3,38531P 30,9738 10032S 31,9721 100

S 32,9715 0,789

S 33,9679 4,43336S 35,9677 0,018

Cl 34,9689 100

Cl 36,9659 32,39979Br 78,9183 100

Br 80,9163 97,940

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ng v Khi lng thng gp tng i127I 126,9044 100

3. Ion mnhc sinh ra khi phn t b phn mnh do va chm vi electron.

4. Ion metastabin

Mt s ion xut hin nh bc trung gian gia cc ion c khi lng ln m1 v m2 c

thi gian sng ngn khng ghi nhn c y cng vch ph nhng cng c th pht

hin c s c mt ca n gi l ion metastabin m* m m* = m2/m1. Nh m* ta c th

khng nh c m2 l do m1 sinh ra.

5.2. C ch phn mnhS phn ho phn t cc hp cht hu c qua s va chm vi e thng xy ra theo

nhng quy lut nht nh, da vo nhng quy lut ngi ta c th gii thch c cu to

cc hp cht hu c.

5.2.1. Ankan.

Nhng ankan v nhng hp cht cha nhm ankyl b ph v di s hnh thnh ca

mt ion ankyl v 1 gc.

RH2CH2C

H2C CH3

RCH2CH2CH2+

+ CH3.

Nhng ankyl gn vi cc nhm chc X = OH, SH, OR th trc tin s tch nhm

chc trc.

[CH3CH2-X] CH3CH2+ + X.

5.2.2. Anken

RH2C CH

CH2 RH2C

H

C CH2 H2C CH CH2 + R

5.2.3. C ch tch ion tropylium (vng)

Cc hp cht benzen c nhm th CH2X (X=H, ankyl, OH, SH, -COR) gn vi

vng benzen thng tch gc R. cho cc ion tropylium theo c ch sau:

C6H5-CH2-R+. C7H7-R C7H7

++ R.

R=H: m/e = 91

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H2C X

- X.

CH2

+

5.2.4. Ancol

Bc 1

R

OH R

CH2 + CH2OH

H3CH2C

H2C OH H2O + H3C C

HCH2

.CH2OH + CH3CH2

+

H2C OH + CH3CH2.

CH2=CH+

+ H2O +.

CH3

Bc 2

RHC OH

R,

H3CH2CH2CHC OH H2O +

CH3

H3CH2CHC CHCH3

H3CHC OH+ CH3CH2CH2.

H3CH2CH2C CH

OH +.CH3

H3CH2CH2C C OH + H.

CH3

Bc 3

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R C OH

R,

R

H3CH2C C OH

H2O +

CH3

H3CHC CCH3

H3CH2C C OH +.CH3

H3C C OH

CH3

CH3

CH3

CH3

+ CH3CH2.

OH

CO +

5.2.5. Andehyt - Xeton

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CH

H2C

CH2

C

O

H

R

H

R CH

CH2 + H2C CH

OH

RCH2CH2CH2.

+ HC O

RH2CH2CH2CC O + H.

CH

H2C

CH

C

OHR

H

H

CH

H2C

CH

C

OH2R

H

HC

H2C CH

CHR

-H2O

CHO

-H.

C O

- CO - C2H2C4H3

+

R, C R

O

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H3CH2C

H2C C CH2CH2CH2CH3

O

H3CH2CH2CC OO C CH2CH2CH2CH3

H3C CH

CH2 + H2CC

OH

CH2CH2CH3 H2C C CH2CH2CH2CH3

OH

5.2.7. Axit

H

OH

O

R1

R2

CH2

R1

H

R2

OH

OH

H

R1 R2

+

+ .COOH

H CH3

R1 R2

+ CO2

H C

R1 R2

O

+ HO.

H C

R1 R2

O

+ H2O

5.2.8. Este

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R C O

OR

R C O +.OR

R C O

O

+ R+

R+

+.COOR

R.

++COOR

5.2.9. S khi ca mt s mnh ion thng gp trong ph MS

m/e Mnh ion m/e Mnh ion

14 CH2 28 CO, NH2

15 CH3 29 C2H5

16 O, CH4 43 C3H7

17 OH, NH3 44 CO2

18 H2O, NH4 45 COOH

19 F 77 C6H5

20 HF

5.3. Nguyn l cu to khi ph k

Khi ph k gm 4 phn chnh

- Ho kh mu: cc cht rn hay lng c a vo bung mu c p sut gim 10 -6

mmHg bin thnh dng kh. Lng mu cn 0,1 1 mg.

- Ion ho: dn dng phn t kh chy qua mt dng electron c hng vung gc vi

n ion ho mu ri i qua in trng U tng tc.- Tch ion theo khi lng

- Nhn bit cc ion bng detect.

Ho kh mu Ion hoPhn tch

ionDetect

X l s liuHo kh mu

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5.3.1. Ho kh mu

Cc mu c np vo ph k c th dng kh, lng hay rn. Trc tin mu cnp vo mt bung kn di p sut thp t 10-5 n 10-7mmHg v nhit t nng c th

ln n 2000C. Di iu kin ny th hu ht cc cht lng v rn u bin thnh th hi.

5.3.2. Ion ho mu

Mu sau khi ho hi c dn vo bung ion ho bin cc phn t trung ho

thnh cc ion. Qu trnh ion ho ny c th thc hin theo mt s phng php khc nhau

nh:

- Phng php va chm electron: mu cht dng hi c dn vo trong mt bung, y c mt dng e mang nng lng chuyn ng vung gc vi mu v xy ra va chm

gia chng, bin cc phn t trung ho thnh cc ion phn t hoc cc ion mnh. Nng

lng ca dng e vo khong 10ev n 100ev. Sau dng ion mi c to ra, chy qua

mt in trng E lm tng tc chuyn ng, th ca in trng c gi l th tng

tc U. Phng php ny c dng ph bin.

- Phng php ion ho ho hc: cho dng phn t kh va chm vi mt dng ion dng

hoc ion m bin cc phn t trung ho thnh ion phn t hay ion manh. Trong qu trnhny, trc tin phi bin cc phn t kh metan thnh ion, sau cc ion ny mi va chm

vi cc phn t mu

- Phng php ion ho trng: cho mu dng hi i qua gia hai in cc cm ng c

mt in trng mnh, di tc dng ca lc tnh in, phn t trung ho s bin thnh cc

ion dng.

- Phng php ion ho proton: cho dng phn t mu dng hi v p vi dng photon

c nng lng khong 10ev s xy ra qu trnh ion ho.

- Phng php bn ph nguyn t nhanh: mt dng kh agon hay xenon c bn ra t

mt khu sng p thng vo mu ho tan trong dung mi nh glixerin. Trc tin cc phn

t dung mi b ion ho ri chnh n ion ho phn t mu thnh cc ion tip theo.

5.3.3. Tch cc ion theo s khi

Cc ion hnh thnh c s khi m/e c phn tch ra k hi nhau bng cc thit b khc

nhau nh:

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- Thit b phn tch hi t n

- Thit b phn tch hi t kp

- Thit b phn tch ion t cc5.3.4. Detect

Cc ion i ra t b phn tch c cng nh nn cn khuych i pht hin. Mt

trong nhng thit b ny l my nhn electron. N to ra cc e th cp khi c e ban u p

vo b mt tm kim loi. khuych i khong 106 khi s dng 16 dint.

5.3.5. Ghi nhn tn hiu

Cc tn hiu t b khuych i truyn ra c np vo b nh my tnh v x l kt

qu ri in ra ph. Cc ph c biu din di dng phn trm basic (%B), nh cao nht ccng 100%, cc nh khc nh hn. Dng ph MS c hnh dng sau:

50

100M+

m/e

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