1.
2 Aldehydes and Ketones
1.2.2 Structure of Aldehydes and Ketones
• The carbonyl carbon of an aldehyde or ketone is sp2-hybridized.
• The bond angle is close to 120° (trigonal planar).
• The carbon-oxygen double bond consists of:
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1.2 Aldehydes and Ketones
1.2.3 Properties of Aldehydes and Ketones
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1.2 Aldehydes and Ketones
1.2.3 Properties of Aldehydes and Ketones
Explanation: In considering the properties of aldehydes and ketones, it must be noted that the carbonyl group present in both
molecules is polar, and hence the compounds are polar. Oxygen is more electronegative than carbon, and the cloud of
electrons that makes up the carbon-oxygen double bond is therefore distorted toward the oxygen. In addition, ketones and to
a lesser extent aldehydes may exist in equilibrium with the “enol” form. This property and the polar nature of the carbonyl lead
to higher boiling points for aldehydes and ketones compared with nonpolar compounds of comparable molecular weight.
Because of the high electron density on the oxygen atom, aldehydes and ketones can hydrogen bond to water and will
dissolve, to some extent, in water. The hydrogen bonding is similar to that suggested for ethers but stronger.
"Keto" – "enol" equilibrium of acetone
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1.2 Aldehydes and Ketones
1.2.3 Properties of Aldehydes and Ketones
As the nonpolar hydrocarbon portion increases,
the effect of the polar carbonyl group on overall
solubility will decrease. This is illustrated in
Table 9-1, where it is apparent that as the
hydrocarbon portion increases beyond two or
three carbons, the water solubility decreases
rapidly in both aldehydes and ketones. Some
water solubility is still possible, however, with
a total carbon content of five or six carbons.
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1.2 Aldehydes and Ketones
1.2.4 Reactions
The reactions of aldehydes and ketones can be divided into two main categories:
The most important chemical property of the carbonyl group is its
tendency to undergo nucleophilic addition reactions of the type
represented in the general equation:
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1.2 Aldehydes and Ketones
1.2.4 Reactions
Carbonyl Group Reactions
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1.2 Aldehydes and Ketones
1.2.4 Reactions
Carbonyl Group Reactions
N/B: Steric and electronic effects influence the
rate of nucleophilic addition to a protonated
carbonyl group in much the same way as they do
for the case of a neutral one, and protonated
aldehydes react faster than protonated ketones.
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