Figure 1.

B3LYP/6-311++G(d,p) calculated minimum energy structures of benzoic acid, 2-fluorobenzoic acid and 2-chlorobenzoic acid, with adopted atom numbering. The values of the O=C-O-H, C6-C-C=O and C2-C-C=O dihedral angles (in ^o) are given in parentheses by this order (the first using bold style). Relative energies are given in square parentheses (in bold), in kJ·mol⁻¹. Each depicted non-planar structure has a symmetry-related form. The cis benzoic acid conformer is also two-fold degenerate, while the trans conformer 4-fold symmetry degenerate.