Chapter 9 Aldehydes and Ketones Chemistry 20

Carbonyl group C = O Aldehydes Ketones Carboxylic acids Esters

In an aldehyde, at least one H atom is attached to a carbonyl group. In a ketone, two carbon groups are attached to a carbonyl group. Aldehydes and Ketones C = O

Step 1 Select the longest carbon chain that contains the carbonyl group (C=O). Step 2 Number from the end nearest C=O group. Step 3 Change the ending of parent alkane from -e to -al. No number for carbonyl group C=O (it always comes first). Step 4 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain. Naming Aldehydes

Common names for the first two aldehydes use the prefixes “form” (1C) and “acet” (2C) followed by “aldehyde”. H─C─H CH 3 ─ C ─HCH 3 ─CH 2 ─ C ─H methanal ethanal propanal (formaldehyde) (acetaldehyde) Naming Aldehydes = O = O = O

CH 3 ─CH─CH 2 ─ C─H 3-Methylbutanal Cl─CH 2 ─CH 2 ─ C─H3-Chloropropanal CH = O = O

Step 1 Select the longest carbon chain that contains the carbonyl group (C=O). Step 2 Number from the end nearest C=O group. Step 3 Change the ending of parent alkane from -e to -one. Use the number to show the location of C=O. Step 4 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain. Naming Ketones

In the common name, name the “alkyl groups” alphabetically attached to the carbonyl group and add the word “ketone”. CH 3 ─ C ─CH 3 CH 3 ─C─CH 2 ─CH 3 Propanone 2-Butanone (dimethyl ketone) (ethyl methyl ketone) = O = O

3-Chloro Cl

Physical properties of Aldehydes and Ketones 1.They have strong odors (ketones have pleasant odors). 2.They are polar compounds. 3.Only dipole-dipole interactions (no hydrogen bonding). 4.Low boiling points compare to amines and alcohols. 5.Soluble in water (no soluble in nonpolar compounds). δ+ δ- δ+ δ- H O H δ+ Hydrogen bond with water. Higher than hydrocarbons. C-O = 1

Chemical properties of Aldehydes and Ketones 1. Oxidation: only for aldehydes (not for ketones). K 2 Cr 2 O 7 H 2 SO 4 CH 3 ─CH 2 ─CH 2 ─CH 2 ─C─OH = O CH 3 ─CH 2 ─CH 2 ─CH 2 ─C─H = O Pentanal Pentanoic acid K 2 Cr 2 O 7 : Oxidizing agent Liquid aldehydes are sensetive to oxidation. No oxidizing agent

Tollen’s Test (Silver-mirror test) Tollens’ reagent is specific for the oxidation of aldehydes (not for ketones).

Chemical properties of Aldehydes and Ketones 2. Reduction: Like reducing the alkene (C = C) to alkane (C – C): –Reduction of an aldehyde gives a primary alcohol (-CH 2 OH). –Reduction of a ketone gives a secondary alcohol (-CHOH-). H 2 transition metal catalyst + 1-Pentanol CH 3 ─CH 2 ─CH 2 ─CH 2 ─C─ H = O Pentanal CH 3 ─CH 2 ─CH 2 ─CH 2 ─CH 2 ─ OH H 2 transition metal catalyst + CH 3 ─C─CH 2 ─CH 3 = O CH 3 ─CH─CH 2 ─CH 3 - OH 2-butanol 2-butanone

Chemical properties of Aldehydes and Ketones Reduction mechanism: NaBH 4 Sodium borohydride: produces hydride ion: H - - Reducing agent

Reduction by NaBH 4 does not affect a carbon-carbon double bond or an aromatic ring. Advantage of NaBH 4 : H3O+H3O+ Chemical properties of Aldehydes and Ketones

3. Addition of alcohols (hemiacetals): H of the alcohol adds to the carbonyl oxygen and OR adds to the carbonyl carbon. unstable Chemical properties of Aldehydes and Ketones

O-CH 2 CH 3 H COCH 2 CH 3 H O CH 2 CH 3 + Ethanol An Acetal COCH 2 CH 3 H O-H A hemiacetal + H2OH2O Acid 3. Addition of alcohols (Acetals):

3. Addition of alcohols (hemiacetals): If –OH is part of the same molecule that contains C=O. Chemical properties of Aldehydes and Ketones