CH223 This lecture’s objectives: Welcome Objectivesncsu/CH223_fall_02/223fall12...This lecture’s objectives: ©Dr. ... What is carbon’s H hybridization? Betty. 4 19 Bonding in

1

1

Welcome

O

O

OH

H

O

H

OH

CH223Kay Sandberg, Ph.D.

2

ObjectivesThis lecture’s objectives:

©Dr. Kay Sandberg

1) Review CH101, CH221 basic concepts2) Introduce arenes & aromaticity

3

Domino effect

©Dr. Kay Sandberg

Get started on the right foot!Strategy for success

Understanding lecture workUnderstanding homework

Understanding exams

Understanding organic chemistry

4

Will you make an A?

©Dr. Kay Sandberg

Students who have an A daily average, butfail exams have not progressed past the “what”.

Organic chemistry:

What?

Why?How?

C students (at best)

B studentsA students

Fred

5

Energy consideration

CH101 reviewReactions:

Understand species in nature tend to react to lower the system’s free energy:

Sandberg’s analogy:

E

increasing E = increasing discomfort

©Dr. Kay Sandberg

Higher Ereactants

Highest E transition state

Lower E products

relatively highenergy species

C C O Barney

6

The secret


Understand Coulomb’s Law:Oppositely charged species are attracted to each other.

©Dr. Kay Sandberg

Find the negative, find the positive,

The SECRET!!!!!

and let the negative “grab” the positive

(and conversely, species oflike charge are repelled.)

2

7

Terms

©Dr. Kay Sandberg

Secret of your success in CH223Find the negative charge carrierFind the positive charge carrier

neg (electrons) “grabs” pos

electrons are now the bond

Lewis base Lewis acide- pairdonor

e- pairacceptor

nucleophile electrophile

likeslikes

8

The secret in scientific terms


©Dr. Kay Sandberg

The SECRET!!!!!

Find the negative, find the positive,

and let the negative “grab” the positive

Find the nucleophile, find the electrophile,

and let the nucleophile bond w/ the electrophile

9

Electron flow arrows

C O

H

H

H

H

©Dr. Kay Sandberg

Wilma: A) Select the appropriate diagram.B) Select the electrophile.

H FC O

H

H

H

LP

F

σ bond

σ bond

LP

red blue

δ+ δ-Up or downin E?

10

ArenesH

H

H

H

H

H

© Kay Sandberg

Section 11.1Chapter 11: Arenes & Aromaticity

CH3

H

H

H

H

H

H

H

H

H

H

H

H

H

benzene toluene

naphthalene

11

Drugs

O

OH

© Kay Sandberg

F3C

OHN

H

aspirin

Prozac

N

OOCH3

O

O

H3C

cocaine

12

BiomoleculesO

O

H3N HHN

O

O

H3N HHO

CH3

H

O

HO

H

H

© Kay Sandberg

estrone

tryptophan

O

O

H3N H

phenylalanine

tyrosine

3

13

Aromatic vs aliphatic

© Kay Sandberg

Section 11.1Chapter 11: Arenes & Aromaticity

Conjugated Conjugatedcyclic

Special stability

Aromaticity

Aromatic HC Aliphatic HC

arenes14

Rxn comparison

© Kay SandbergSection 11.2

x,y-dibromo-a,b-hexadieneNo Rxn

Aromatic HC Aliphatic HC

Br2 CCl4Br2 CCl4

x,y-dibromocyclohexene

Br2 CCl4

15

Hydrogenation

© Kay Sandberg

Section 11.2

ExcessH2 Pd

16

Hydrogenation

© Kay Sandberg

Section 11.2

PdH2

17

Substitution

© Kay Sandberg

Section 11.2X

Y

Substitution productsare obtained readily

Aromatic ringis retained.

18

Hybridization in benzene C

CC

C

CC

H

H

H

H

H

HWhat is carbon’shybridization?

Betty

4

19

Bonding in benzene

© Kay Sandberg

Section 11.3Structural features of benzeneC6H6

120o

120o

120o

140 pm

sp2- sp2

single bond 146 pm

double bond 134 pm

6

54

3

21

1

2

6

5

4 3

20

Resonance in benzene

© Kay Sandberg

Section 11.5

6

54

3

21

43

21

6

5

Resonance6

54

3

21

Pebbles

21

Representations of toluene

© Kay Sandberg

Section 11.5

6

54

3

21

43

21

6

5

Resonance

It is common, however, for chemists to use one of the 2 resonance structures, but you should realize that reality is in between the 2 resonance structures.

toluene toluene

6 pi electronsare obvious

22

Bonding in conjugated aliphatic

Section 11.5

© Kay Sandberg

C CC

HH

H

HC

CC

CC

H

H

H

H

H

CH

CH

H

H

C CH

HH

Weaker πinteractions

Stronger πinteractions

Longer bonds

Shorter bonds

23

Bonding in aromatic

© Kay Sandberg

Section 11.5

Same length

Same strength πinteraction

No alternation24

Sigma & pi bonding in benzene

© Kay Sandberg

Section 11.7

6 pure 2p orbitals6 π electrons

Continuous π system

σ system

sp2 hybridized C

π system

C

CC

C

CC

H

H

H

H

H

H

5

25

Heats of hydrogentation

© Kay Sandberg

Section 11.6

E kJ

/mol 360

231 208

120

“

“

3 x 120H2 + 2 X 120 = 240

9 kJ conjugationstabilization

(3 x 120) – (2 x 9) = 342 kJ

3H2 +

2H2 +

Bam Bam

26

Empirical resonance energy

© Kay Sandberg

Section 11.6Here we have 6 π-e’sthat are lower in Ethan 4 π-e’s

E kJ

/mol 360

231 208

152

120

“

“

3 x 120

Empiricalresonanceenergy

H2 +

3H2 +

2H2 +

27

Stability of benzene

© Kay Sandberg

Section 11.6Stability of benzene

E kJ

/mol 360

231 208

152

120

“

“

3 x 120

Empiricalresonanceenergy

Hydrogenation:Rh or Pt, orhigher pressures,

higher temperatures.3H2 +

H2 +

2H2 +

28

Stability of benzene

© Kay Sandberg

Section 11.6Stability of benzeneE

kJ/m

ol

337

129

208

Large stabilizationdue to π-e-’sbeing aromatic.

3 nonconjugateddoublebonds

360

23

Small stabilizationdue to π-e-’s beingconjugated, but notaromatic.

29

Solubitilty

© Kay Sandberg

Section 11.9

Physical properties of arenes•nonpolar•water insoluble•less dense than water

CCl4H2O

benzene 0.88

1.00

1.59

density (g/mL)

Dino

beforemixing

aftermixing 30

Nomenclature

© Kay Sandberg

Section 11.7Nomenclature of benzene & derivatives

bromobenzene

Br NO2

tert-butylbenzene

nitrobenzene

6

31

Special names

© Kay Sandberg


benzaldehyde

O

H

O

OH

benzoic acid

32

Special names

© Kay Sandberg


O

CH3OH

acetophenone phenol

When the benzene ring is a substituent it isnamed phenyl (C6H5-)

Rubble

33

Special names

© Kay Sandberg


anisole aniline

toluene

OCH3

NH2

CH3

styrene

George 34

Monosubstituted derivatives

1-phenylheptane

© Kay Sandberg

Section 11.7

butylbenzene

hexylbenzene

12

34

12

34

56

12

34

56

7

“benzene” = parent name

“phenyl” = branch name

heptylbenzene

Locantneeded

7 or morecarbons6 or less

carbons

Judy

35

Monosubstituted derivatives

© Kay Sandberg

Write the IUPAC name.

Elroy

36

Disubstituted derivatives

© Kay Sandberg

Section 11.7Nomenclature of benzene derivativesDisubstituted benzenes

Y

X X

Y

X

Yortho(1,2)

o-

meta(1,3)m-

para(1,4)

p-

12

34

5

61

3

2

45

61

4 3

2

5

6

7

37

o/m/p regioprefixes

© Kay Sandberg

Section 11.7Nomenclature of benzene & derivativesDimethyl derivatives: xylenes

o-xylene m-xylene p-xylene1,2-dimethylbenzene

1,3-dimethylbenzene1,4-dimethylbenzene

ortho meta para

CH3

CH3 CH3

CH3

CH3

CH3-xylene -xylene

38

o/m/p regioprefixes

© Kay Sandberg

Section 11.7Nomenclature of benzene & derivativesDisubstituted benzenes

Y

X X

Y

X

Yortho meta para

X

o o

m mp

ipso

39

o/m/p silly memory devices

© Kay Sandberg


ortho meta paraX

o o

m mp

YX

XY

X

Y

40

Practice

© Kay Sandberg


m-bromoisopropylbenzene

Br

Astro

meta-bromoisopropylbenzenealso acceptable

41

Trisubstituted derivativesNO2

Cl

O2N


When parent is benzene, # to give the lowestlocant at the first point of difference (beforealphabetizing).

5

43

2

16 NO2

Cl

O2N1

65

4

32 NO2

Cl

O2N4

56

1

23 NO2

Cl

O2N

1-chloro-2,4-dinitrobenzene

1,3,4-trisubstituted 1,2,4-trisubstituted1,2,5-trisubstituted

o/m/p only used for disubstituted derivatives –cannot use for tri or higher substituion

Ignore di, tri, tetra, etc. when alphabetizing42

Numbering rule

© Kay Sandberg

Section 11.7Nomenclature of benzene derivatives

When parent is benzene, # to give the lowestlocant at the first point of difference (beforealphabetizing). (Highest priority rule)

When 2 differing numbering schemes are lowest,then use the one which gives the lowest locantto the branch listed first alphabetically.

1.

2.

8

43

Practice with special namesCH3

NO2O2N

NO2

© Kay Sandberg

Section 11.7

F

OCH3

CH3CH2

Nomenclature of benzene derivatives

anisole

tolueneUnderstood C-1

Understood C-1

4-ethyl-2-fluoro

2,4,6-trinitro anilineUnderstood C-1

6

54

3

21

CH3

NO2O2N

NO2

NH2

CH3

CH2CH3

4

56

1

23 F

OCH3

CH3CH2

6

54

3

21

NH2

CH33

45

6

12

NH2

CH3

amino

toluene derivative? aniline derivative?

means no locant 1 in name 3-ethyl-2-methyl

Rosey

44

PrioritiesOH

© Kay Sandberg

Section 11.7Nomenclature of benzene derivatives

propan-1-ol

When the benzene ring is a substituent it isnamed phenyl (C6H5-)

3-phenyl

32

1OH

36

Use name to double checkcarbon #.

Alcohol has priority which means it isbonded to the parent.

Number from endwhich gives thehydroxy group the lower locant.

45

More practice

© Kay Sandberg

Section 11.7Which is (Z)-2-phenylbut-2-ene?

H3C

CH3

H

Hi

Lo

Hi

Lo

“zame zide”

Spacely

(Z)-(E)-

46

Benzyl vs phenyl

© Kay Sandberg

Section 11.7

Benzyl group (C6H5CH2-)

Br

benzyl bromide

Br

phenyl bromide

CBr

HH

methylene kink

ring is parentbromine branch

bromobenzene

ring is branchbromide is parent

47

Benzyl vs allyl

© Kay Sandberg

Section 11.7

Br

benzyl bromide

benzylic Br

Br

Benzyl is analogous to allyl

allyl bromide

allylic Br

48

Benzylic vs allylic vs aryl

© Kay Sandberg

Section 11.12

C CC

CCC C

H

HBr

HH

Cl

H H

CC C

H

HBr

H

HCl

Vinylic H & Cl

Benzylic H & Br

“arylic”aryl H & Cl

Allylic H & Br

9

49

Aryl vs alkyl

© Kay Sandberg

Section 11.7Nomenclature of benzene & derivativesThe adjective “aryl” is analogous to “alkyl”.

aryl Calkyl C

H

aryl H

H

alkyl H

Cosmo 50

Reaction overview

2. Influence of aryl group as a substituenton the reactivity of another functional groupto which it is attached.

© Kay Sandberg

Section 11.10Reactions of arenes1. Ring as functional group.

Birch reductionElectrophilic aromatic substitution (EAS)

Benzyliccarbocation

Benzylicradical

alkenylbenzene

Nucleophilic aromatic substitution (NAS)

C C CC

51

Radical formation comparison

© Kay Sandberg

Section 11.12Free-radical halogenation of alkylbenzenes

CH

H

H

C

H

H

H

C HH3C

H3CCH3

CH

H

C

H

H

C

H3C

H3CCH3 H+

H+

H+

ΔHo

397 kJ/mol

368 kJ/mol

tert-butyl rad

allyl rad

52

Radical resonance delocalizsation

©Dr. Kay Sandberg

CC

CH

H

H

H

H

CC

CH

H

H

H

H

CC

CH

H

H

H

H

δ.δ.

i.e., Resonance delocalization

53

Benzyl radical formation

© Kay Sandberg

Section 11.12Free-radical halogenation of alkylbenzenes

CH

H

H

C

H

H

H

C HH3C

H3CCH3

CH

H

C

H

H

C

H3C

H3CCH3 H+

H+

H+

ΔHo

397 kJ/mol

368 kJ/mol

356 kJ/mol

tert-butyl rad

allyl rad

benzyl rad 54

Resonance structures

© Kay Sandberg

Section 11.12Stability of benzyl radical

3 2

1

65

4 CH

H

3 2

1

65

4 CH

H

3 2

1

65

4 CH

H

3 2

1

65

4 CH

H

Resonance delocalized:

Jane

10

55

Resonance structures


3 2

1

65

4 CH

H

3 2

1

65

4 CH

H

3 2

1

65

4 CH

H

3 2

1

65

4 CH

H

Notice where the rad is not!

Tom 56

Radical stability chart

© Kay Sandberg

Section 10.3

EC C

CH

H

H

H

H

RC

RR

RC

RH

RC

HH

HC

HH

C HCH2 vinyl radical (least stable)

allyl radical

radical stabilitiesradical stabilities

C CC

HH

C

H

CCC

H

HH

H

benzyl radical (most stable)

57

Radical orbital picture

© Kay Sandberg

Section 11.12Stabilization due to overlap of benzylic pure p orbitalwith the extended π system of ring

Benzyl radical

58

Benzylic vs aryl H abstration

© Kay Sandberg

Section 11.12Regioselectivity of H abstraction

HH

Abstraction of aryl HAbstraction of benzylic H

radical ⊥ to π system less stable

sp3p

59

Radical stability chart

© Kay Sandberg

Section 10.3

EC C

CH

H

H

H

H

RC

RR

RC

RH

RC

HH

HC

HH

CH H2C vinyl radical (least stable)

allyl radical

radical stabilitiesradical stabilities

C CC

HH

C

H

CCC

H

HH

H

benzyl radical (most stable)60

Benzylic vs aryl radical

© Kay Sandberg

Section 11.12Regioselectivity of H abstraction

HH

Abstraction of aryl HAbstraction of benzylic H

benzylic vinylic (“arylic”)

11

61

Free radical halogenation step 1

© Kay Sandberg

Section 11.12Regioselectivity of free-radical halogenation

Cl Cl Cl + Cl

hν

The homolytic cleavage of the Cl-Cl bond to create the atomic chlorine atoms.

62

Step 2

C

H

H

H Cl+

Section 11.12Free radicals: alkylbenzene

Step 1 initiation

Cl Cl C l + Cl

hν

Step 2 propagation

CH

HH Cl+

H atom abstraction from toluene by Cl atom generating benzyl radical

© Kay Sandberg

benzyl radical

63

Step 3


Step 1 initiation

Cl Cl C l + Cl

hν

C

H

H

H Cl+

Step 2 propagation

C

H

H

H Cl+

Chain propagation

C

H

H

Cl Cl+ C

H

H

Cl Cl+

Benzyl • reacts with molecular Cl creating atomic Cl ...© Kay Sandberg

64

Benzylic chlorination


CH H

H

light

CH Cl

H

Cl2

toluene

© Kay Sandberg

Cl2

light

CH Cl

Cl

Cl2

light

CCl Cl

Cl

benzyl chloride

(dichloromethyl)benzene

(trichloromethyl)benzene

65

Benzylic bromination


CH H

H

light

CH Br

H

NO2 NO2

Br2+CCl4, 80oC

© Kay Sandberg

p-nitrotoluene p-nitrobenzyl bromide

+ HBr

66

NBS benzylic bromination

© Kay Sandberg

ethylbenzene 1-bromo-1-phenylethane

CBr C

H

H

H

HH

H

H

H

H

NH

O

O

+NBS


CH C

H

+CCl4, 80oC

H

H

HH

H

H

H

H

NBr

O

O

peroxide

12

67

NBS benzylic brominationO

CH

H

HH

H

C

NO2

H

HBr

H

Section 11.12

OC

+CCl4, 80oC

H

H

HH

H

C

NO2

H

NBr

O

O

peroxide

HH

H

© Kay Sandberg

NH

O

O

+

O

NO2

Br

OC

+CCl4, 80oC

H

H

HH

H

C

NO2

H

NBr

O

O

peroxide

HH

H

Jerry

Documents

CH223 This lecture’s objectives: Welcome Objectivesncsu/CH223_fall_02/223fall12...This lecture’s objectives: ©Dr. ... What is carbon’s H hybridization? Betty. 4 19 Bonding in