Carbonyl Compounds We have already seen a number of carbonyl compounds

47 Pages·2014·1.27 MB·English

by  Michael Biewer

Carbonyl Compounds

We have already seen a number of carbonyl compounds

O O O O O O
R R R H R NH R OH R OR R Cl
2
Ketone

Amide

Ester

two R groups

one R, one N

one R, one OR

Aldehyde

Acid

Acid chloride

one R, one H

one R, one OH

one R, one Cl

In this chapter, the focus is on the reactivity of ketones and aldehydes
Nomenclature of Ketones and Aldehydes

Many of the same IUPAC rules already learned apply

With ketones: suffix is –one

With aldehydes: suffix is -al

In numbering, the carbonyl takes precedence over previous functional groups learned

O O O
HO H
2-butanone

4-hydroxy-2-butanone

propanal

(carbonyl precedence

(do not need to write 1)

over alcohol)
Common Names

In addition to the IUPAC naming, many ketones and aldehydes have common names

O O O
CH
3
H C CH H C H H
3 3 3
acetone

methyl ethyl ketone

formaldehyde

(name two alkyl groups)

The aceto- common name is consistent amongst many compounds

O O O
H C H C OH H C O
3 3 3
aceto-

acetic acid

ethyl acetate
The properties of ketones and aldehydes are dependent on the structure

The carbonyl double bond is a result of a π bond between the carbon and oxygen

Due to electronegativity of oxygen, this double bond is more polarized than an alkene

O O
R
C O
R R R R R
The increase in proportion of charged structure in resonance hybrid causes two effects:

1)  Carbonyl carbon is more electrophilic

(compared to alkene)

2)  Oxygen is more nucleophilic

(compared to alkene)
Can observe differences by looking at electron density maps

H H
O
H H H H
Physical properties of ketones and aldehydes

Two main physical properties are a direct result of carbonyl functionality:

1)  Ketones and aldehydes have a higher boiling point than alkanes of similar mass

A result of having a greater charged component in the resonance hybrid

(charged structures have a higher boiling point and melting points than uncharged)

2)

Ketones and aldehydes have a higher water solubility compared to alkanes

H
O
H
Due to hydrogen bonding capability

O
of carbonyl oxygen

R R
Synthesis of Ketones and Aldehydes

We have already seen many ways to synthesize ketones and aldehydes
Other Routes to Ketones and Aldehydes

Many carbonyls can be converted to other types of carbonyls

(chapter 21 focuses on many of these interconversions)

Carboxylic acids can be converted to ketones with organolithium reagents

O R Li O OH
R Li
OH
H C OH H C O H C
3 3 3 R
First equivalent of organolithium abstracts hydrogen

O
Second equivalent reacts at carbonyl

H C R
3
Upon protonation generate geminal diol

Geminal diols equilibrate with ketone
Acid Chlorides can be Converted to Either Aldehydes or Ketones

The carboxylic acid can first be converted to an acid chloride

The acid chloride can be reduced to an aldehyde with lithium tri(t-butoxy) hydride

Need to use lithium tri(t-butoxy) hydride since it is weaker than LAH

(LAH would reduce aldehyde to alcohol)
Acid Chloride to Ketone

As seen earlier with most carbon based nucleophiles (e.g. Grignard reagents)

two equivalents will react with an acid chloride to yield a tertiary alcohol

Dialkyl cuprates (Gilman reagent), however, only one equivalent adds to yield a ketone