AbstractContrary to literature data 1‐isopropylcyclohexanol afforded both 1‐isopropylcyclohexanecarboxylic acid and 2‐cyclohexyl‐2‐methylpropanoic acid upon carboxylation by the method ofKoch.The Koch‐Haaf carboxylation of a number oftert‐alkyl substituted cycloalkane derivatives has been studied. Side reactions were suppressed by using the Haaf conditions with slow stirring of the reaction mixture.tert‐Butylcyclohexanols afforded 1‐tert‐butylcyclohexanecarboxylic acid accompanied by 2‐methyl‐2‐(1‐methylcyclohexyl)propanoic acid. In the Koch‐Haaf reaction of 3‐tert‐butylcyclopentanol and 4‐tert‐butylcycloheptanol more complex rearrangements occurred. The main products were 1,2,2‐trimethylcyclohexanecarboxylic acid and 2‐cyclohexyl‐2,3‐dimethylbutanoic acid, respectively.From the composition of the reaction products conclusions were drawn concerning the mechanisms of the rearrangements involved in these reactions. In some of the reactions protonated cyc