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.