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Chapter 8 Spectroscopic methods of structure determination. 结构测定的波谱方法. Introduction Ultraviolet Spectroscopy (UV) 紫外光谱 ---- 测定有机物中是否存在共轭双键和芳香族化合物 Infrared Spectroscopy (IR) 红外光谱 ---- 测定有机物中官能团。 - PowerPoint PPT Presentation
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Chapter 8Spectroscopic methods of structure determination
结构测定的波谱方法
Introduction
1. Ultraviolet Spectroscopy (UV) 紫外光谱 ---- 测定有机物中是否存在共轭双键和芳香族化合物
2. Infrared Spectroscopy (IR) 红外光谱 ---- 测定有机物中官能团。
3. Nuclear Magnetic Resonance Spectroscopy (NMR) 核磁共振谱 ---- 测定有机物中不同类型的氢或碳的数目和位置。( 1H NMR and 13C NMR)
4. Mass Spectrometry (MS) 质谱 ---- 测定有机物的分子量。
The characteristics of spectroscopic determination
1. Microscale sample (1 – 5 mg, 样品少 )2. It need short time to determine sample( 时间短 )3. Identify structure very fast.( 结构确认快而准 )4. Most are nondestructive ( 多不破坏样品 )
重点 : 了解简单原理 , 简单识谱
Wavelength
波长 λcm10-9 γ-rays
10-7 X-rays ionization
10-5Vacuum UV
( 真空紫外 )
10-4Near UV
( 近紫外 ) Electronic transition
电子跃迁
UV-vis
紫外 - 可见光谱10-3
Visible(vis)
( 可见光 )
10-1Infrared(IR)
( 红外 )
Molecular vibration
分子振动
IR
红外光谱
10-2Microwave
( 微波 )
Rotational motion
10-4Radio
( 无线电波 )
Nuclear spin transition
核自旋跃迁
NMR
核磁共振谱
The electromagnetic spectrum电磁波谱
¦Ë=
hcE = hv
• UV spectoscopy observes electronic transitions and provides information on the electronic bonding in the sample.
1. Ultraviolet spectroscopy( 紫外光谱 , 15-13, p 666)
1) Spectral region of UV: 200-400nm
2) Ultraviolet light and electronic transition ( 紫外光与电子跃迁 )
σ→ σ*
π→ π*
n→ π*
n→ σ*ΔE
σ
π
π*
σ *
nE
UV
π→ π* : K 带 , 吸收峰强 , 共轭双键增加 , 向长波方向移动 , B 带 , 苯的吸收带 , 宽 230~270 nm, 中心 254 nm
E 带 , 把苯环看成乙烯键或共轭乙烯键跃迁引起的吸收带 .
n→ π*: R 带 , > 270 nm, 吸收峰较弱 , C=O, C=N, -NO2
Wavelength
Absorptance
π→ π* : K 带
n→ π*: R 带
A compounds that contain a longer chain of conjugated double bonds absorbs light at a longer wavelength.共轭体系增加 , 吸收波长增大 , 即吸收“红移”
¦Ëmax
methanol
171 nm
217 nm
CH2=CH2
258 nm
CH2=CHCH=CH2
CH2=CHCH=CHCH=CH2
CH2=CHCH=CHCH=CHCH=CH2 290 nm
增大
¦Ëmax
methanol171 nm ¦Ëmax
methanol217 nm
CH2=CH2 CH2=CHCH=CH2
HOMO
LUMO
HOMO
LUMO
excitationexcitation
¦Ð¦Ð1
¦Ð2
¦Ð* ¦Ð*
¦Ð*E
nerg
y
β – Carotene 胡罗卜素
Lycopene 番茄红素
¦Ëmax
methanol
497 nm (red orange) (Visible region)
¦Ëmax
methanol
505 nm (red) ( Visible region )
β – Carotene 胡罗卜素
¦Ëmax
methanol
497 nm (red orange) (Visible region)
¦Ëmax
methanol
505 nm (red) ( Visible region )
C O
O
C
O
O
HO OH HO O
酚酞
酸式结构 , 无色 碱式结构 , 红色
3) Obtaining an UV spectrum
detector检测仪
source光源
monochromator单色器
sample cell样品池
reference cell
Ir
Is
recorder记录仪
A
λ
UV 测定常用溶剂 : CH3OH, CH3CH2OH
Is --- 透过样品的光强度Ir --- 透过空白样的光强度
A----absorbance 吸光度ε--- molar extinction coefficient 摩尔消光系数c----molar concentration of sample , mol/Ll-------the length, cm 液层厚度
A = logIr
Is= ¦Å c lLambert-Beer Rule
朗伯-比尔定律
UV principle
¦Ëmax
methanol
171 nmCH2=CH2
CH2=CHCH2CH=CH2
CH2=CHCH=CH2
¦Ëmax
methanol
178 nm
¦Ëmax
methanol217 nm
non conjugate system
conjugate system
4) Interpreting UV spectra ( 解谱 )
(1) 判断有无共轭体系存在,或有无芳烃、醛、酮、羧酸、芳胺等有机物。
每增加一个共轭双键,波长增加 30~40 nm; 每增加一个烷基取代基 , 波长增加约 5 nm.
See: Table 15-2 (p 671)(problem: 15-3, 15-22)
发色基;
O O N O NO
O
C
O
C
ON=N
±½õ« ÑÇÏõ »ù Ïõ »ù 1£¬2-¶þͪ »ù żµª»ù
2,5-Dimethyl-2,4-hexadiene
¦Ëmax
methanol242.5 nm ( ¦Å= 13.100 M-1 cm-1 )
(2) 共轭链连有未共用电子对基团如: -NH2, -NR2, -OH, -OR, -SR, -Cl, -Br, -I, 可产生 p~π 共轭,使化合物颜色加深, λmax 向长波方向移动 ----- 把这样的基团称为助色基.
记录格式
苯在己烷中的吸收光谱 联苯类化合物的紫外光谱图
logε ε
λ/nm λ/nm
280nm (ε13500); 295nm (ε27000)
顺式: 由于位阻,共轭不是太好,故波长短, ε 小些反式: 共轭效果好,故波长增加, ε 增大
Assignment : T-1, 15-28; T-2 , 8-2
2. Infrared spectroscopy (IR, 红外光谱 , 12-1~12, p 490-519)
IR spectroscopy observes the vibrations of the bonds and provides evidence of the functional groups present.
1) Spectral region of IR: 中红外 : λ2.5-25 μm ( 波数 4000~400 cm-1)
V =¦Ë
1-²¨Êý;Wavenumber
2) Molecular vibrations and IR spectroscopy
Stretching vibration伸缩振动
Bending vibration弯曲振动
symmetric stretching antisymmetric stretching
Rocking Twisting Scissoring wagging
ν :振动频率k:化学键的力常数μ :折合质量
Frequency: decreases with increasing atomic weight; increase with bonding energy.键能越大,折合质量越小,频率越高,峰出现在高波数区.
like a spring
IR principle
entry bond bond energy (kJ) stretching frequency(cm-1)
1 C-H 420 3000
2 C-D 420 2100
3 C-C 350 1200
4 C=C 611 1660
5 C≡C 840 2200
6 C-N 305 1200
7 C=N 615 1650
8 C≡N 891 2200
9 C-O 360 1100
10 C=O 745 1700
Bond stretching frequency (Table 12-1)
entry bond bond energy (kJ) stretching frequency(cm-1)
1 C-H 420 3000
2 C-D 420 2100
3 C-C 350 1200
4 C=C 611 1660
5 C≡C 840 2200
6 C-N 305 1200
7 C=N 615 1650
8 C≡N 891 2200
9 C-O 360 1100
10 C=O 745 1700
Frequency range of functional groups
<1500, fingerprint region指纹区
1500-3600, functional group region官能团区
IR-active and IR-inactive vibration
偶极矩变化越大,红外吸收越强. 偶极矩变化与以下因素有关 : 电负性 ( 电负性差别大,吸收强 ) 、 振动方式 ( 不对称伸缩 > 对称伸缩 > 弯曲振动 ) 分子的对称性 ( 对称性差,吸收峰强 ) 氢键 ( 使吸收峰变宽变强 )
problem 12-2
只有分子振动时偶极矩( dipole moment )发生变化的振动( Δμ≠0 )才有红外吸收。偶极矩 μ=δ× d
• A polar bond is usually IR-active.
• A nonpolar bond in a symmetrical molecule will absorb weakly or not at all.
3) Measurement of the IR spectrum
Infrared spectrometer ( 红外光谱仪 )
A Nicolet 800 FT-IR, 400 to 4000 cm-1 )
红外测定方法:
1. KBr disc (KBr压片法 ) 2. 液膜法( NaCl盐片 ) 3 石腊油法
4) Characteristic absorptions of common functional groups( 常见官能团的特征吸收 )
hydrocarbons ( 烃 ):
bond frequency bond frequency
-C-H 2800-3000 C-C 1200
=C-H 3000-3100 C=C 1660
C=C-C=C 1620
Ar-H 3000-3100 C=C (Ar) 1600, 1500
≡C-H 3300 C≡C 2100-2200
stretching frequency(cm-1)
CH3(CH2)6CH3
CH3: 1380
Alkane
CH3(CH2)3CH=CH2Alkene
Alkyne
benzene
toluene
Aromatic compounds
=C-H
Alcohols and amines ( 醇和胺 ):
bond frequency
-O-H3300, broad with rounded tip, srong
-NH23300, broad with spikes ( 尖峰 ) ,middle( 中强 ), two sharp spikes
-NHR one sharp spike
-NRR’ no N-H
Alcohol
Amine
EthersC - O - C 1150-1070 [strong]
1120
bond frequency
C=O 1710 (strong)
ketone ( 酮 ) 1710 (strong)
aldehyde ( 醛 ) 1710 (strong)
acid 1710 (strong)
ester ( 酯 ) 1750-1730 (strong)
amide ( 酰胺 ) 1690-1650 (N-H: 3300)
C=C-C=O 1685-1665 (strong)
O=C-H 2720, 2820
O=C-O-H 3300-2500 (broad)
carbonyl compounds ( 羰基化合物 ):
Usually, it’s the strongest IR signal.
Ketone
Aldehyde
Carboxylic acid
Amide
1681C=O
3348, 3173N-H
Acetamide, 乙酰胺
Carbon - Nitrogen Stretching
• C - N 1200 cm-1.• C = N 1660 cm-1 and is much stronger than
the C = C absorption in the same region.• C N absorbs strongly just above 2200 cm-1.
The alkyne C C signal is much weaker and is just below 2200 cm-1 .
A Nitrile IR Spectrum
=>
Summary of IR Absorptions
红外光谱主要是获得有机物官能团信息.
(1) 吸收峰的位置、强度和形状。(2) 先特征峰,后一般峰。先强峰,后次强峰,
再中强峰,同时注意峰形,宽,尖,单峰或双峰。相关峰。
与标准图谱对照可以确认化合物。
5) Interpretation of the IR spectra ( 红外光谱解析 )
3-pentanone CH3CH2COCH2CH3 Diethyl ketone
C5H10O
1716
C7H8O
3400 cm-1: strong OH peak present. 3100 cm-1: weak peak suggesting sp2 CH 2900 cm-1: weak peak suggesting sp3 CH. 1610 , 1497 , 1454 cm-1: peaks suggesting Ar C=C
OH
C8H8O
3100 cm-1: moderate peak suggesting sp2 CH 2900 cm-1: weak peak suggesting sp3 CH 1690 cm-1: strong carbonyl absorbance 1600 cm-1: Ar C=C
O
C7H6O
3100 cm-1: moderate peak suggesting sp2 CH. 2720 , 2820 cm-1: moderate peak suggesting aldehyde CH. 1700 cm-1: strong carbonyl absorbance. 1600 cm-1: bands consistent with Ar C=C.
O
H
C4H8O2
¦¸ = 1
1760 cm-1: strong carbonyl absorbance.
2900 cm-1: minor peak suggesting sp3 CH. CH3C
O
OCH2CH3
Assignments
• Text-1: p 533-538: 12-15, 16, 25
• Text-2: p 222: 5, 6, 7
3. Mass Spectrometry (质谱)
• Molecular weight can be obtained from a very small sample.
• It does not involve the absorption or emission of light.
• A beam of high-energy electrons breaks the molecule apart.
• The masses of the fragments and their relative abundance reveal information about the structure of the molecule.
1) Mass spectrometer ( 质谱仪 )
进样系统 ion sourse离子源
magnetic deflection
高真空系统
detector
Electron Impact Ionization
A high-energy electron can dislodge an electron from a bond, creating a radical cation (a positive ion with an unpaired e-).
e- + H C
H
H
C
H
H
H
H C
H
H
C
H
H
H
H C
H
H
C
H
H
+ H
H C
H
H
C
H
H
H
+
2) The mass spectrum ( 质谱图 )
molecular ion peak ( 分子离子峰 ): M+, 一般为偶数 , 含奇数氮时为奇数 .base peak ( 基峰 ): 丰度 100%isotopic peak ( 同位素峰 ): 13C (1.1%)
m/z
M+: 86
AlkaneAbundance 丰度
1. 产物稳定性原则:正碳离子的稳定性顺序为叔> 仲 > 伯;2. 最大烷基丢失原则:失去的烷基愈大,裂解反应愈有利,因而对应的产物离子丰度愈高。
Common peaks: 15 (CH3
+), 29 (CH3CH2+), 43 , 57, 71……
More stable carbocations will be more abundant.
Alkene
烯丙基裂解 m/z = 41
Resonance-stabilized cations favored.
Alcohol and ether
醇、醚等易发生
46, M+
HO CH3
3-methylheptan-3-ol
M+: 130
解释 115, 101, 73 三个峰
HO CH3分别是 115(M+-CH3) 、 101(M+-C2H5) 、 73(M+-C4H9)
• Alcohols usually lose a water molecule.• M+ may not be visible.
=>
Isotopic Abundance 同位素丰度
81Br
Molecules with Heteroatoms
• Isotopes: present in their usual abundance.• Hydrocarbons contain 1.1% C-13, so there will be
a small M+1 peak.• If Br is present, M+2 is equal to M+.• If Cl is present, M+2 is one-third of M+.• If I is present, peak at 127, large gap.• If N is present, M+ will be an odd number.• If S is present, M+2 will be 4% of M+.
同位素峰
=>
同位素峰
=>
同位素峰
Application of MS
• MS can provide informations shown below: molecular weight ( 分子量 , 由 M+) molecular formular (high resolution mass spect
roscopy, HRMS)( 分子式 , 高分辨质谱 ) heteroatom ( 杂原子 , 由同位素峰、 M+ 等可知 ) functional group ( 官能团,由碎片峰等知 ) alkyl substituents ( 烷基取代基,由碎片峰等知 )
• NMR is the most powerful tool available for organic structure determination.
• It is used to study a wide variety of nuclei:– 1H– 13C– 15N– 19F– 31P
4. Nuclear Magnetic Resonance Spectroscopy (NMR, 核磁共振谱 )
1H NMR--- 核磁共振氢谱,给出有机物中含有多少氢原子及其位置。
13C NMR--- 核磁共振碳谱,给出有机物中含有多少碳原子及其位置。
Nuclear Spin 核的自旋
凡是原子的原子序数或质量数为奇数时,如 1H, 13C, 19F, 31
P, 原子核能发生自旋( spin )。自旋的核类似于一个磁棒。
Principle of NMR
External Magnetic Field (外加磁场)在外加磁场中,自旋的核就象一个小磁棒,其产生的磁矩有两种取向 , 分别与外加磁场方向相同或相反 , 有低 / 高两个能态 , 其中低能态多。
stateµÍÄÜ̬
state¸ßÄÜ̬
E B0
E = r2
hB0
= r2
1B0
用能量为 ΔE= hν 的无线电波射频辐射 , 使核由低能态跃迁至高能态 , 则称核发生了共振,产生核磁共振信号 .
The NMR spectrometer ( 核磁共振仪 )
Using Deuterium 氘 solvents dissolve sample for NMR determinations. CDCl3, D2O, CD3OD, D6-DMSO.
1H NMR 核磁共振氢谱
Shielding and Deshielding of Protons ( 质子的屏蔽和去屏蔽)
¸ÐÉú́ų¡
µç×Ó»·Á÷
B0
Ô ×ÓºË
有机化合物中的 H 核外有电子云,在磁场作用下产生的磁矩与外加磁场方向相反,削弱了外加磁场对核的照射,称为屏蔽( shielding )。反之,称为去屏蔽( deshielding )。 不同化学环境下的 H 核其核外电子云不同,受到的屏蔽也不同。质子的外层电子密度越大,则屏蔽越大,需要增大外加磁场才能使核跃迁,发生共振,因此质子的信号出现在高场;反之出现在低场。
=>
H H
H H
H H
B0
benzene去屏蔽 , 出现在低场 alkyne
屏蔽 , 出现在高场
C
C
H
H
B0
π 电子的作用
B0
C CH H
HH
alkene , (aldehyde proton)去屏蔽 , 出现在低场
σB0
H
H
HH
H
H
H
H
H
H
H
HH
H
H
H
H
H
µÍ³¡¸ß³¡
[18] Annulene(轮烯 ). The internal protons are highly shield. The external protons are highly deshielded.
The chemical shift 化学位移 δ
由于分子中氢所处的化学环境不同,显示不同的吸收峰,峰与峰之间的差距,就称为化学位移 δ ( chemical shift).
参比试剂: Si(CH3)4, 四甲基硅烷 tetramethylsilane (TMS)
610
核磁共振仪所用频率
参比样品
ppm
CH3
CH3
1.01.5
4H 6H
δ = 2.30 ppmδ = 7.05 ppm
化学位移与氢的电子云密度有关 , 密度越大 , 化学位移越小 , 信号出现在高场 ; 反之 , 化学位移大 , 信号出现在低场 . 信号强度与质子数成正比 , 通过积分峰面积可以得知氢的相对数目 .
低场 高场
=>
Approximate proton chemical shifts.
The number of signals
Ha
HbHb
Ha
Hc
X
单取代苯 , 三种 H, 故可能给出多重峰
H3CH2C CH2CH3
e. CH3COOCH3
f. CH3COOCH(CH3)2
a. CH3CH3
b. CH3CH2CH3
c. CH3OCH3
d.
1
2
1
3
2
3
(n+1) rule: 与某一个质子邻近的等价质子数为 n 时,核磁共振信号裂分为( n+1 )重峰,其强度如下:
Signal splitting( 信号裂分) : spin-spin coupling (自旋 - 自旋偶合)
Cl2CHCH2CHBr2 中的 CH2应裂分为( 1+1) (1+1) = 4
重峰,且此四重峰强度相等。
与某一质子的邻近质子不相同时,裂分数目为 (n+1)(n’+1)(n”+1) 重峰。
13C NMR( 核磁共振碳谱 )
• 12C has no magnetic spin.
• 13C has a magnetic spin, but is only 1% of the carbon in a sample.
• The gyromagnetic ratio of 13C is one-fourth of that of 1H.
• Signals are weak, getting lost in noise.
• Hundreds of spectra are taken, averaged.
Hydrogen and Carbon Chemical Shifts
=>
Combined 13C and 1H Spectra
注 : N 上 H 在 10.8 ppm
用 IR, 1H NMR, MS综合分析推出未知物的结构C5H10O
C5H10O
C5H10O
septetÆßÖØ·å
singletdoublet
CHCH3
CH3
CH3C
O
C5H10O
CHCH3
CH3
CH3C
OH3C C O
N
HO
N
HOTs
N
HO
N
HOTs
Summary
• 由氢谱可知有机化合物中氢的种类(化学位移)、数目(峰强度积分)和相互关系(偶合常数)。
• 对一些简单化合物由氢谱即可确定其结构。
• 作业: T-1 p-594, 13-36, 38• T-2 15 , 16 , 17 , 21 , 23