Answer
Effect of Alkyl Groups on Acidity
Alkyl groups exert a +I inductive effect that destabilizes the carboxylate anion, thereby lowering the acidity of carboxylic acids.
As the number of alkyl groups increases, the acid becomes progressively weaker.
Formic acid (HCOOH): No alkyl group – strongest acid
Acetic acid (CH₃COOH): One methyl group – weaker than formic acid
Isobutyric acid ((CH₃)₂CHCOOH): Two methyl groups – even weaker
Pivalic acid ((CH₃)₃CCOOH): Three methyl groups – weakest acid
Order of acidity: HCOOH > CH₃COOH > (CH₃)₂CHCOOH > (CH₃)₃CCOOH