Ch. 15 Chem (Aldehydes and Ketones)

Carbonyl Group

A functional group that has a carbon atom joined to an oxygen atom by a double bond (C=O)

Carbonyl Compound

Any compound with a carbonyl group

Bond angles of the carbonyl group

120 degrees, trigonal planar

Aldehyde

A compound that has a carbonyl group bonded to at least one hydrogen, RCHO; always ends a carbon chain

Ketone

A compound that has a carbonyl group bonded to two carbons in organic groups that can be the same or different, RCOR’. Always within a carbon chain

Aldehydes and Ketones boiling points

Aldehydes and Ketones cannot bond to themselves, they bond to water.

Therefore, they have higher boiling points than alkanes, but have lower boiling points than alcohols.

IUPAC Naming of Aldehydes

• The final -e of the name of the alkane with the same number of carbons is replaced by -al

• When substituents are present, the chain is numbered beginning with the carbonyl carbon

Common Naming of Aldehydes

• The simplest aldehydes are known by their common names, which end in -aldehyde

IUPAC Naming of Ketones

• The final -e of the corresponding alkane name is replaced by -one. The numbering of the alkane chain begins at the end nearest the carbonyl group.

Common Naming of Ketones

• Give the names of the two alkyl groups bonded to the carbonyl carbon followed by the word ketone

• List the longer alkyl group second, not in alphabetical order

Properties of Aldehydes and Ketones

• Moderately polar

• Soluble in common organic solvents

• Simple ketones are excellent solvents

• Common aldehydes and ketones are typically liquid

• Distinctive odors

Common Aldehydes

• Formaldehyde (HCHO)

• Acetaldehyde (CH3CHO)

• Acetone (CH3COCH3)

• Benzaldehyde (PhCHO

Formaldehyde

HCHO

Acetaldehyde

CH3CHO

Acetone

CH3COCH3

Benzaldehyde

PhCHO

Oxidation of Aldehydes

• Alcohols can be oxidized to aldehydes or ketones. Aldehydes can be further oxidized to carboxylic acids.

• In aldehyde oxidation, the hydrogen bonded to the carbonyl carbon is replaced by an -OH group

• Ketones do not react with oxidizing agents

Tollens’ Reagent

Consists of a solution containing silver ion in aqueous ammonia. Treatment of an aldehyde with this reagent rapidly yields the carboxylic acid anion and metallic silver.

Benedict’s Reagent

Contains blue copper (II) ion, which is reduced to give a precipitate of red copper(I) oxide in the reaction with an aldehyde

Tollens’ Reagent > (is better than) Benedict’s Reagent

Benedict’s reagent does not unequivocally distinguish between ketones and aldehydes

Reduction of Aldehydes and Ketones

• Aldehydes and ketones can be reduced to alcohols

• Aldehydes are reduced to primary alcohols, and ketones are reduced to secondary alcohols

• The reduction of a carbonyl group occurs with the addition of hydrogen across the double bond to produce an -OH group

Addition Reactions

Aldehydes and ketones undergo addition reactions in which an alcohol combines with the carbonyl carbon and oxygen

Hemiacetals

• Initial product of addition reactions with alcohols

• Hemiacetals have both an alcohol-like -OH group and an ether-like -OR group bonded to what was once the carbonyl carbon atom

• The H from the alcohol bonds to the carbonyl-group oxygen and the OR from the alcohol bonds to the carbonyl-group carbon

Acetal

A compound that has two etherlike groups bonded to what was the carbonyl carbon atom

Hydrolysis

A reaction in which a bond or bonds are broken and the H- and -OH of water add to the atoms of the broken bond or bonds

Acetal Hydrolysis

Requires an acid catalyst and a large quantity of water to drive the reaction back toward the aldehyde or ketone