Studies on cyclohexane derivatives: IV Preparation and chemical proof of the configurations of the two 4‐isopropylcyclohexanecarboxylic acids

The preparation of pure low‐melting 4‐isopropylcyclohexanecarboxylic acid (m.p. 40–41°) is described for the first time. It was isolated from mixtures of the low‐melting and the high‐melting isomer, making use of the fact that only the latter gives an inclusion compound with thiourea. By chemical means it is proved that low‐melting 4‐isopropylcyclohexanecarboxylic acid has the cis‐configuration and the high‐melting isomer the trans‐configuration. For this purpose these acids were converted into cis‐ and trans‐1‐methyl‐4‐isopropylcyclohexane (cis‐ and trans‐para‐menthane) respectively, using reactions which take place without any change of configuration at the cyclohexane nucleus. The configuration of these two hydrocarbons has been proved in paper III of this series.