Carbonyls

(1)

Finishing Chapter 21

Chapter 16

Chapter 16 Chapter 16 -

-- Intro to Carbonyls

-

Intro to Carbonyls

Chapter 15

Chapter 15 Chapter 15 -

-- Highlights

-

Highlights

Grignard

Grignard and Gilman reagents

and Gilman reagents

Lecture 11

Sessler 310N

(2)

(3)

Recommended Problems CH’s 20; 21 Recommended Problems CH’s 20; 21 20.4, 20.6, 20.7-20.10, 20.16, 20.17, 20.4, 20.6, 20.7-20.10, 20.16, 20.17, 20.19-20.32, 20.43, 20.46-20.4820.19-20.32, 20.43, 20.46-20.48 21.2, 21.4, 21.5, 21.7-21.9, 21.2, 21.4, 21.5, 21.7-21.9, 21.11, 21.14-21.22, 21.24-21.26, 21.30-21.4321.11, 21.14-21.22, 21.24-21.26, 21.30-21.43

Exam I will cover spectroscopy (MS, IR,

Exam I will cover spectroscopy (MS, IR, NMR, UV-Vis)NMR, UV-Vis)

and Aromaticity (Chapts. 12-14; part of 23; 20 and 21.1-21.2) and Aromaticity (Chapts. 12-14; part of 23; 20 and 21.1-21.2)

NOTE:

NOTE: NO NO OFFICE OFFICE HOURS HOURS TOMORROW TOMORROW (SORRY).(SORRY). However, …

However, …

There is a review session Tonight (5 pm;

(4)

D

i

D

Dii-

-- a

-

a

an

a

nd

n

d P

d

Poly

P

olys

oly

sub

s

ubs

ub

sttit

s

t

itut

it

ution

ut

ion

z

z Existing groups on a Existing groups on a benzene ring influence further benzene ring influence further

substitution in both

substitution in both orientationorientationorientationorientation and rateand rate

z

z Orientation:Orientation:

–

– certain subscertain substituents direct tituents direct preferentially topreferentially to orthoortho && para para positions; positions;

others direct preferentially to

others direct preferentially to metameta positions positions

–

– substituents asubstituents are classified re classified as either as either

ortho

ortho---- para para para para directing or directing or directing or directing or

meta directing

(5)

D

i

D

Dii-

-- a

-

a

an

a

nd

n

d P

d

Poly

P

olys

oly

sub

s

ubs

ub

sttit

s

t

itut

it

ution

ut

ion

z

Rate:

–

– certain substituents cause the rate of a second

certain substituents cause the rate of a second

substitution to be greater than that for benzene

itself; others cause the rate to be

lower

itself; others cause the rate to be

itself; others cause the rate to be lower

lower

–

– substituen

substituents are classified as

substituen

ts are

classified as

•

• activatingactivatingactivatingactivating toward further substitution, ortoward further substitution, ortoward further substitution, ortoward further substitution, or •

•

• deactivatingdeactivatingdeactivatingdeactivating preventing or slowing furtherpreventing or slowing furtherpreventing or slowing furtherpreventing or slowing further

substitution substitution substitution substitution

(6)

Di

Di-- and

and Polysubstitution

Polysubstitution

z -OCH₃ is ortho- para directing and activating.

p -bromo-anisole (96%) o -bromo-anisole (4%) anisole + + B r B r B r ₂ CH ₃ CO ₂ H HBr

OCH₃ OCH₃ OCH₃

zTHE MECHANISTIC EXPLANATION ACCOUNTING FOR

(7)

Di

Di-- and

and Polysubstitution

Polysubstitution

z

-NO

₂

is meta directing and deactivating!

m-Dinitro-benzene (93%) Nitro-benzene + + + o-Dinitro-benzene p-Dinitro-benzene Less than 7% combined NO ₂ NO ₂ NO ₂ NO ₂ NO ₂ NO ₂ NO ₂ HNO ₃ H2 SO 4

(8)

Toluene undergoes nitration

1000 times faster than

benzene.

A methyl group is an

activating

activating substituent.

Methyl Group

CH

₃₃

(9)

Relative rates of

Nitration

OH H Cl NO₂ 1000 1.0 0.033 6x10-8 Reactivity Reactivity

(10)

Halogen

Halogen Substituents

Substituents

Cl

Chlorobenzene undergoes

nitration ca. 30

times more slowly than

benzene .

Halogens are deactivating

deactivating

substituents..

But, they are

o

p

,,

p

directors!!

directors

(11)

Theory of Directing Effects

• So…what’s going on here????

• The rate of EAS is limited by the slowest step in the mechanism…duh

• For EAS, the rate-limiting step is attack of E+ _{on the} aromatic ring to form a resonance-stabilized cation intermediate

• The more stable this cation intermediate, the faster the rate-limiting step and the faster the overall reaction

• In the case of halogen, competing effects are at work! Back to…

(12)

Real Fast Real Fast

Pretty fast Pretty fast

Kinda

Kinda slowslow

Pretty slow Pretty slow Slow Slow Real Slow Real Slow

(13)

To Review:

To Review: Effect on

Effect on Regioselectivity

Regioselectivity

••

Ortho-- paraOrtho para directorsdirectors

direct an incoming

electrophile to positions ortho and/or para to

themselves.

•

Meta directors Meta directors

direct an incoming electrophile to

positions meta to themselves.

•

All meta directors All meta directors

are deactivating

••

All ortho All ortho-- para para

directors are activating

except except

(14)

Polysubstitution

Polysubstitution--

--General Rules

General Rules

z Where more than one substituent exists on a benzene ring,

look to see if one is significantly more activating than the

other. If this is the case and open ortho and/or para site(s)

are available, the incoming electrophile will substitute at these latter sites.

z Groups such as -OR and -NR ₂ dominate over more weakly

activating groups, such as alkyl groups, and halogens

z If groups are similarly activating or deactivating and they

are not oriented to direct towards the same position (s),

such as in the case of 1,3-dinitrobenzene, horrible mixtures can result.

(15)

Chemistry 310N

The wrong way….

CH₃ NO₂ Na₂Cr₂O₇ H₂SO₄ CO₂H NO₂ HNO₃ H₂SO₄ CO₂H NO₂ CO₂H NO₂ NO₂ NO₂ +

The right way…

CH₃ NO₂ Na₂Cr₂O₇ H₂SO₄ CO₂H NO₂ HNO₃ H₂SO₄ CH₃ NO₂ NO₂ NO2

(16)

ortho

ortho Nitration of Toluene

Nitration of Toluene

+

H

CH

₃₃

H

NO

₂₂

Be sure you can write the remaining Be sure you can write the remaining resonance structures and then do the resonance structures and then do the same for

same for metameta and for and for para para attack.attack.

And one last “minimum expectation” review problem:

Practice going from your list of structures to a coherent argument about which products will be formed in preference and why.

(17)

Chemistry 310N

End of Material That will be Covered on Exam I

Note how Sect. 21.3, Nucleophilic Aromatic

Substitution, is not going to be on the Exam or, in fact, covered in the course.

(18)

Carbonyl Chemistry I

Lecture 10 Cont.

(19)

(for this lecture)

15.13, 15.14a

(20)

C

O

+

C

O

(21)

- The Carbonyl Group

The Carbonyl Group

z

Over the course of several chapters we will

study the physical and chemical properties

of classes of compounds containing the

carbonyl group, C=O

– aldehydes and ketones (Chapter 16 (+15.1))

– carboxylic acids (Chapter 17)

– acid halides, acid anhydrides, esters, amides

(Chapter 18)

(22)

nucleophiles attack carbon;

electrophiles attack oxygen

Resonance Description of

Carbonyl Group

C

O

••

• _•

C

O

+

–

••

• • •

•

(23)

The Carbonyl Group

z

The carbonyl group consists of

– one sigma bond formed by the overlap of sp2 _hybrid orbitals, and

– one pi bond formed by the overlap of parallel 2p orbitals

C σ O

(24)

The molecule is planar

bond angles: close to 120°

C=O bond distance: 1.22 Å

Structure of Formaldehyde

(25)

Carbon and oxygen are

sp

22

_hybridized

Bonding in Formaldehyde

(26)

The

The pp orbitals on carbonorbitals on carbon and oxygen overlap to and oxygen overlap to

form a

form a ππ bondbond

Bonding in Formaldehyde

(27)

Nomenclature

Nomenclature--Aldehydes

Aldehydes

z

IUPAC names: select as the parent alkane

the longest chain of carbon atoms that

contains the carbonyl group..subtract e and

add al

– because the carbonyl group of the aldehyde must be on carbon 1, there is no need to give it a number

z

For unsaturated aldehydes, show the

presence of the C=C by changing -an- to

-en- – the location of the suffix determines the numbering pattern

(28)

Nomenclature

Nomenclature--Aldehydes

Aldehydes

3-Methylbutanal 2-Propenal (Acrolein) O O CH₃ CHCH₂ CH CH₂ =CHCH _H O (2E)-3,7-Dimethyl-2,6-octadienal (Geranial) 1 2 3 4 5 6 7 8 1 1 2 2 3 3 4 O CH₃ CH₂ CH₂ CH₂ CH Pentane Pentanal 1 2 3 4 5 CH₃

(29)

4,4-dimethylpentanal

5-hexenal

Nomenclature of

Nomenclature of Aldehydes

Aldehydes

H

O

_O

H

O

HCCHCH

O

2 2--phenylpropanedial

(30)

when named

as a suffix it is

when named as

a substituent this is a

formyl

formyl group

group

_carbaldehyde

carboxaldehyde

C

_H

O

Nomenclature of

(31)

Nomenclature

Nomenclature--Aldehydes

Aldehydes

z

For cyclic molecules in which the -CHO group is

attached to the ring, the name is derived by adding

the suffix -carbaldehyde to the name of the ring

2-Cyclopentene-carbaldehyde 2,2-Dimethylcyclo-hexanecarbaldehyde CHO CH ₃ CH ₃ CHO 3 1 1 2 2

(32)

2 2--heptanone

heptanone

(component of alarm

pheromone of bees)

O

Many

Many aldehydes

aldehydes and ketones occur naturally

and ketones occur naturally

trans

--2

2--hexenal

hexenal

(alarm pheromone

of

of myrmicine

myrmicine ant)

ant)

O

(33)

Structure of Ketones

z The functional group of a ketone is a carbonyl

group bonded to two carbon atoms

CH₃-C-CH ₃ O Propanone (Acetone) O Cyclohexanone

(34)

Trivial Nomenclature of Ketones

CH

₃

CH

₂

CCH

₂

CH

₂

CH

₃

O

ethyl propyl ketone

benzyl ethyl ketone

divinyl ketone

O

CH

₂

CCH

₂

CH

₃

CH

₂

O

H

₂

C

CHC

(35)

IUPAC Nomenclature

IUPAC Nomenclature--Ketones

Ketones

z

IUPAC names:

– select as the parent alkane the longest chain that contains the carbonyl group,

– number to give C=O the smaller number and then subtract e and add one

subtract e and add one

5-Methyl-3-hexanone Propanone (Acetone) O _O CH₃ CCH₃ _CH 3 CH2 CCH2 CHCH3 1 2 3 4 5 6 O 1 2 3 4 5 6 7 Bicyclo[2.2.1]-2-heptanone CH₃

(36)

IUPAC Nomenclature

IUPAC Nomenclature--Ketones

Ketones

z

z Even the IUPAC system retains the commonEven the IUPAC system retains the common

names acetone,

names acetone, acetophenoneacetophenone, and, and benzophenone benzophenone

1-Phenyl-1-pentanone CCH₂CH₂CH₂CH₃ O 1 2 3 4 5 Benzophenone Acetophenone CCH₃ O O C-CH₃CCH₃ O Acetone

(37)

IUPAC Nomenclature of Ketones

CH

₃

CH

₂

CCH

₂

CH

₂

CH

₃

O

CH

₃

CHCH

₂

CCH

₃

O

CH

₃

3-hexanone

4-methyl-2-pentanone

CH

₃

CH

₂

CCH

₂

CH

₂

CH

₃

O

ethyl propyl ketone

O

O H

(38)

Order of Precedence

(Pecking order)

z For compounds that contain more than one functional

group indicated by a suffix

mercapto- amino- oxo- hydroxy- oxo--thiol -amine -ol -one -al -oic acid Prefix if Lower in Precedence Suffix if Higher in Precedence Functional Group C=O -CHO -CO₂ H -OH -NH ₂ -SH P r e c e d e n e