Organic Chemistry

I

n Section 17.0, we saw that carbonyl com-

pounds—compounds that possess a carbonyl

group —can be divided into two

classes: Class I carbonyl compounds, which have a

group that can be replaced by a nucleophile, and

Class II carbonyl compounds, which comprise aldehydes

and ketones. Unlike Class I carbonyl compounds, Class II carbonyl compounds do not

have a group that can be replaced by a nucleophile.

The carbonyl carbon of the simplest aldehyde, formaldehyde, is bonded to two

hydrogens. The carbonyl carbon in all other aldehydesis bonded to a hydrogen and to

an alkyl (or an aryl) group. The carbonyl carbon of a ketoneis bonded to two alkyl (or

aryl) groups. Aldehydes and ketones do not havea group that can be replaced by

another group, because hydride ions and carbanions and are too basic to be

displaced by nucleophiles under normal conditions.

The physical properties of aldehydes and ketones are discussed in Section 17.3 (see

also Appendix I), and the methods used to prepare aldehydes and ketones are summa-

rized in Appendix IV.

Many compounds found in nature have aldehyde or ketone functional groups.

Aldehydes have pungent odors, whereas ketones tend to smell sweet. Vanillin and

cinnamaldehyde are examples of naturally occurring aldehydes. A whiff of vanilla

extract will allow you to appreciate the pungent odor of vanilla. The ketones carvone

and camphor are responsible for the characteristic sweet odors of spearmint leaves,

caraway seeds, and the camphor tree.

O

CCC

H H R H RR'

formaldehyde

O

an aldehyde

O

a ketone

(H-) (R-)

(C“O)

18

Carbonyl Compounds II

Nucleophilic Acyl Addition, Nucleophilic Acyl

Substitution, and Nucleophilic Addition–Elimination •

Reactions of , -Unsaturated Carbonyl Compoundsab

731

formaldehyde acetaldehyde acetone

formaldehyde

acetaldehyde

acetone