Aldehydes & ketones Chapter 9

Aldehydes & ketones

Chapter 9The carbonyl group The carbonyl group (C=O) is found in aldehydes,ketones, and many other organic functional groups. The carbon and oxygen in the carbonyl group are sp 2 hybridized, with bond angles of 120.

Functional groups containing carbonyl groups

Aldehyde nomenclatureIUPAC:

Aldehyde nomenclatureCOMMON METHOD: the name is created as a derivative of the parent name followed by aldehyde and using the greek alphabet as locators.

Common NameName the following structures using the IUPAC mathod. 1. 2. 3.

4. 5. 6.

Name the following structures using the IUPAC mathod. 1. 2. 3.

butanal 2-ethylbutanal benzaldehyde

4. 5. 6.

hexanal 3-methylbutanal 2-propenal

Ketone nomenclatureIUPAC METHOD:

Ketone nomenclatureCOMMON METHOD: Name alkyl groups that are attached to each side of the carbonyl group in alphabetical order.

Butyl propyl ketone

Name the following compounds in both the IUPAC and common methods.

1. 2. 3.

4. 5.

common name not required

Name the following compounds in both the IUPAC and common methods.

1. 2. 3.

propanone 2-butanone 3,4-dimethyl-2-pentanone dimethyl ketone ethyl methyl ketone methyl (1,2-dimethyl propyl) ketone

4. 5.

3-ethyl-2-pentanone cyclohexanone methyl (1-ethyl propyl) ketone --not required

ADDITIONAL NOMENCLATURE RULES:

Physical properties of carbonyls1. Carbonyls are slightly polar.

Physical properties of aldehydes and ketones1. Carbonyls are slightly polar, however, since there is no hydrogen on the carbonyl oxygen aldehydes and ketones do not form hydrogen bonds with themselves. They can hydrogen bond with water.

Physical properties of aldehydes and ketones2. Carbonyls cause aldehydes and ketones to have higher boiling points than comparable hydrocarbons but lower than comparable alcohols.

Physical properties of aldehydes and ketones3. Low molecular weight aldehydes and ketones are water soluble; water solubility decreases as molecular weight increases.

Physical properties of aldehydes and ketones4. Aldehydes and ketones have distinct odors. Aldehydes are said to have sharp and irritating odors, although as the molecular weight increases the odor improves and becomes pleasant. Large molecular weight aldehydes are often found in perfumes.Ketones have sweet and pleasant odors. Fingernail polish remover, acetone, is a very common household ketone. 19Reactions of aldehydes and ketonesAldehydes and ketones can be produced by the oxidation of alcohols.

Reactions of aldehydes and ketonesAldehydes are easily oxidized, however, ketones do not generally oxidize. This makes oxidation reactions an easy way to distinguish between the two types of compounds. When aldehydes are oxidized they form carboxylate salts.

Common oxidizing agents are: KMnO4 /Chromic Acid and K2Cr2O7 /H2SO4

Reactions of aldehydes and ketonesOxidation of aldehydes:

Tollens reagent is a mild oxidizing agent composed of silver ions in an aqueous basic solution of ammonia. When the aldehyde is oxidized to carboxylate salt and the silver ions are reduced to solid silver, which coats the bottom of the tube with a silver mirror.

Reactions of aldehydes and ketonesOxidation of aldehydes:

Benedicts reagent is a mild oxidizing agent composed of cuprous hydroxide in sodium citrate. When the aldehyde is oxidized to carboxylate salt and the copper ions are reduced to solid copper (I), which precipitates out as a red solid.Reactions of aldehydes and ketonesReduction of aldehydes and ketones:

Aldehydes and ketones are reduced to form alcohols when they react with hydrogen gas in the presence of a catalyst. Common reducing catalysts are nickel, platinum, or palladium. Aldehydes will return to primary alcohols and ketones will return to secondary alcohols.

Reactions of aldehydes and ketonesReduction of aldehydes and ketones:

The most common laboratory reagent for the reduction of an aldehyde or ketone is sodium borohydride, NaBH4. This reagent contains hydrogen in the form of hydride ion, H:-.In a hydride ion, hydrogen has two valence electrons and bears a negative charge.In a reduction by sodium borohydride, hydride ion adds to the partially positive carbonyl carbon which leaves a negative charge on the carbonyl oxygen.Reaction of this intermediate with aqueous acid gives the alcohol.Reactions summary

or carboxylate salt