Aldehydes & Ketones

Experiment 6

Aldehydes & Ketones

INTRODUCTION

Both aldehydes (RCHO) and ketones (R2CH) are under carbonyl compounds which contain a carbonyl (C=O) group. The carbon in aldehydes is attached to a hydrogen atom and an alkyl group while the carbon in ketones is attached to two alkyl groups. The double bond in the carbonyl group is very susceptible to chemical
reactions (Ophardt, 2003). 

Aldehydes and ketones are one of the most common compounds. Some common aldehydes and ketones used are propanone or commonly known as acetone which is chiefly used as a solvent since it is soluble in both water and non-polar organic compounds and also used in nail polish remover, methanal or formaldehyde used to synthesize methanol and many plastics and used in embalming and preservation of biological specimens, ethanal or acetaldehyde used to synthesize many organic compounds, and 3-phenyl-2-propenal or cinnamaldehyde causes the odor and flavor of cinnamon (Ophardt, 2003).

The IUPAC system of nomenclature assigns a characteristic suffix to these classes, al to aldehydes and one to ketones. The names of aldehydes and ketones are simply derived by replacing the suffix "-e" from the root and by "-al" or "-one" respectively (Ophardt, 2003). A position number is needed for ketones since the carbonyl group may be on any number of several carbons in the "middle" of a chain (Ophardt, 2003). The carbonyl on the aldehyde is always on the number one carbon so no position number is needed (Ophardt, 2003).                

Chemical properties of aldehydes and ketones are mostly influenced by the presence of the carbonyl group. Aldehydes and ketones generally undergo nucleophilic addition reaction where a nucleophile approaches the carbonyl group from an angle opposite the carbonyl oxygen and forms a bond to the electrophilic C=O carbon atom. Commonly, aldehydes are more reactive than ketones in nucleophilic addition reactions. The nucleophile can readily approach the carbonyl group of an aldehyde because only one large substituent is bonded to the carbonyl carbon while as there are two large substituents to the carbonyl carbon of a ketone. (McMurry, 2013).

        Many aldehydes and ketones occur naturally and many of them are also synthesized in laboratories (McMurry, 2013). Aldehydes can be synthesized by the process of oxidation of primary alcohols (McMurry, 2013). Alcohols can also be synthesized using partial reduction of certain carboxylic acid derivatives (McMurry, 2013). The process of synthesizing aldehydes may also be used to synthesize ketones (McMurry, 2013). Oxidation of secondary alcohols will yield ketones (McMurry, 2013). Ketones may also be synthesized via the ozonolysis of alkenes in which one of the unsaturated carbon atoms is disubstituted and Friedel-Crafts acylation of an aromatic ring with an acid chloride with AlCl3 as a catalyst (McMurry, 2013).