Molecular Conformations of 4-Aminomethyl-1-cyclohexanecarboxylic Acids in Aqueous Solution

Abstract

Abstract The structures of cis- and trans-4-aminomethyl-1 -cyclohexanecarboxylic acids were studied by proton and carbon-13 NMR, and by semiempirical molecular orbital methods (CNDO/2 and MNDO). Both isomers exist in zwitter ionic forms in aqueous solution. It was found that the most stable conformations for them are all staggered forms: the diequatorial conformer in the trans form and the axial carboxyl group in the cis form. These preferred conformers are similar to those in crystalline states. In these conformers the deformation is very small in the cyclohexane ring of the trans form. The atomic distance between the nitrogen of amino group and the carbon of carboxyl group in the preferred conformer of trans form is 0.65 nm and that in cis form is 0.55 nm. This distance of 0.65 nm will play an important role in the antifibrinolytic effect.