Inelastic Neutron Scattering (INS) Study of Low Frequency Vibrations and Hydrogen Bonding of (E)-Benzil Monoxime

Abstract

(E)-benzil monoxime (or (E)-monoxime of 1,2 diphenyloetandion), which is the subject of this paper, belongs to the family of bioactive organic substances. Many of them have been investigated for many years by inelastic, incoherent neutron scattering spectroscopy (IINS) but the investigation of (E)-benzil monoxime is absent from literature. Therefore (E)-benzil monoxime has been investigated using infrared, and IINS spectroscopy. Dimers of (E)-benzil monoxime were considered using B3LYP functional (connection of Becke and Lee–Yang–Parr functionals) combined with the 6-311++G(d,p) basis set method of quantum chemistry in order to improve the results obtained for a single molecule. In (E)-benzil monoxime, extra bands corresponding primarily to hydrogen bond vibrations (γ bending out of plane of hydrogen bond at 312.3, 372, 470.5, 578.3, 703.5, 748.7, 780.4 cm^–1, σ stretching of hydrogen bond bridge at 124.3, 140.9, 176.5, 190.1, 223.6, 259.1, 290.5, 501.8, 623.5 cm^–1, δ bending in plane of hydrogen bond at 1102.4, 1371,1452,1535, 1630.6 cm^–1, λ bending of hydrogen bond bridge at ca. 40 cm^–1, ν stretching band OH at 3397 cm^–1) have been identified. Some of them could be discovered only by using IINS method and this is the main result of this work. Additionally we'd like to compare the structure of the compound and the structure of oximes previously investigated by us . Taking into account the structure and IINS results for three oximes investigated by us, we can estimate the difference of hydrogen bond power in those three oximes. Hence the power of hydrogen bond in the (E)-benzil monoxime seems to be the smallest in the group of the three compounds: (E)-benzil monoxime, (E)-2-hydroxyimino-2-cyanoacetic acid ethyl ester (2-oxime), acid K salt of 2-oxime.