Which description defines the ester functional group?

Which description defines the ester functional group?

• A. C=O + OH (COOH)
• B. N-containing group
• C. OH alone
• D. C=O + O-R (COO-R)

Answer: (D)

The ester group is defined by a carbonyl carbon that is also bonded to an oxygen which connects to another carbon-containing group. In other words, the structure is R-CO-O-R'. The description that matches this is a carbonyl (C=O) linked to an O-R fragment, written as COO-R. This sets ester apart from other groups: a carboxylic acid has C=O with an OH attached, not O-R; a hydroxyl group is just OH; and the presence of an N-containing group points to amines or amides rather than esters.

The ester group is defined by a carbonyl carbon that is also bonded to an oxygen which connects to another carbon-containing group. In other words, the structure is R-CO-O-R'. The description that matches this is a carbonyl (C=O) linked to an O-R fragment, written as COO-R. This sets ester apart from other groups: a carboxylic acid has C=O with an OH attached, not O-R; a hydroxyl group is just OH; and the presence of an N-containing group points to amines or amides rather than esters.