Neutron-diffraction studies of salicylic acid and α resorcinol*

Abstract

Abstract Investigations of these substances, which have been much examined in the past, have been extended by three-dimensional analysis of single-crystals with neutrons. For salicylic acid the structure was refined to R = 9% for both unconstrained and rigid-body models, with translational motion of 0.15, 0.15, 0.14 Å and librational motions of 4.04, 2.81, 5.17° referred to the throe inertial axes. The intramolecular bond, of length 2.606 Å with O–H = 0.957 Å, is very bent, with an angle of 145° at the hydrogen atom. For resorcinol, R = 3.6% is achieved by an unconstrained refinement, against 6.3% for a rigid body, indicating significant vibrations within the molecule itself. The e.s.d. of the hydrogen coordinates is 0,006 Å and for the O–H bond lengths it is 0.007 Å. The amplitudes of libration of the molecule are 4.37, 2.27 and 2.68°, being substantially greater about the axis which follows the line of the hydrogen bonds.