Hydrogen bond, dimerization and vibrational modes in 2-chloro-3-hydroxybenzaldehyde and 3-chloro-4-hydroxybenzaldehyde from vibrational and ab initio studies.
Ab initio conformers and dimers have been computed at RHF and B3LYP/6-31G* levels for isomers 2-chloro-3-hydroxybenzaldehyde and 3-chloro-4-hydroxybenzaldehyde to explain the observed infrared absorption and Raman vibrational spectral features in the region 3500-50 cm(-1). The position of the chlorine in ortho position with respect to aldehyde group in 2-chloro-3-hydroxybenzaldehyde yields four distinct conformers; whereas the chlorine in meta position in 3-chloro-4-hydroxybenzaldehyde yields effectively only three conformers. Major spectral features as strong absorptions near 3160-80 cm(-1), down-shifting of the aldehydic carbonyl stretching mode and up-shifting of hydroxyl group's in-plane bending mode are explained using ab initio evidence of O-H⋯O bond-aided dimerization between the most stable conformers of each molecule. Absorption width of about 700 cm(-1) (∼8.28 kJ/mol) of O-H stretching modes suggests a strong hydrogen bonding with the ab initio bond lengths, O-H⋯O in the range of 2.873-2.832 Å. A strong Raman mode near 110-85 cm(-1) in each molecule is interpreted to be coupled vibrations of pseudo-dimeric trans and cis structures.
Yenagi
Jayashree
J
Department of Physics, Karnatak University, Pavate Nagar, Dharwad 580003, India. jyenagi.phys.kud@gmail.com
Arlikatti
Nandini V
NV
Tonannavar
J
J
D001547:Benzaldehydes / Q000737:chemistry*; D017606:Chlorine Compounds / Q000737:chemistry; D019281:Dimerization; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D014732:Vibration
D001547:Benzaldehydes; D017606:Chlorine Compounds; D006843:Hydrocarbons, Chlorinated; C011275:3-hydroxybenzaldehyde; C011483:4-hydroxybenzaldehyde