Molecular structure and rotational isomerism in glyoxylicacid from microwave spectroscopy and ab initio calculations

An improved substitution structure for glyoxylic acid in the hydrogen bonded trans-1 form is presented. By means of microwave double resonance spectroscopy, the trans-2 form, with a zig-zag chain of atoms HOCCH, was identified. Using trans-2 dipole moment components calculated by ab initio SCF theory, the energy of the trans-2 form is found to be 1.2 ± 0.5 kcal mole^?1 higher than that of the trans-1 form. The ab initio energy difference (?1.0 kcal mole^?1) has the wrong sign.