CONTROL OF N-HEPTANE CONFORMER POPULATIONS BY METHYL SUBSTITUTION OR RING ANNULATION

The conformations of a flexible n-heptane chain are considered. Six-membered ring annulation at the inner bonds leads to 1,3-disubstituted cyclohexanes, at the outer bonds to dicyclohexylmethane derivatives. Force-field calculations show that these molecules maintain the conformational mobility of the heptane chain to a large degree, yet some populate one particular conformer to more than 80% (up to 99% in the case of 17). The predominant conformers of the molecules described here allow to represent each of the regular (diamond lattice type) conformations of a heptane chain. Moreover, for the open-chain heptane derivatives the effect of methyl substitution on the conformational preferences has been examined. Finally, the adamantane derivative 32 has been identified in giving the heptane chain a 93% preference for the tg+ g+ t-conformation.