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Vibrational and Ab Initio Studies of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin

Vibrational and Ab Initio Studies of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin

Anuradha Ramoji, Jayashree Yenagi, J Tonannavar, V B Jadhav, M V Kulkarni

Spectrochim Acta A Mol Biomol Spectrosc. 2010 Dec;77(5):1039-47.

PMID: 20855229

Abstract:

Infrared absorption and Raman spectra (3500-50 cm(-1)) of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin have been measured and interpreted, aided by electronic structure calculations at RHF and B3LYP using 6-31(d, p) basis set. It has been determined that the rotation of the acetyl group with respect to the coumarin ring results in three conformers--two trans and one cis--for each molecule, with one trans conformer being the most stable in both cases. There are significant changes in the vibrational structure as characterized by positions and intensities of certain modes in going from 3-acetyl-6-bromocoumarin to 3-acetyl-6-methylcoumarin. The carbonyl stretching mode of the pyrone ring is stable in both molecules whereas the same mode in acetyl groups is not. Ring stretching vibrations are coupled to C-H in-plane bending vibrations. Down-shifting of frequencies of methyl vibrations in acetyl group occurs vis-à-vis methyl vibrations in 3-acetyl-6-methylcoumarin. A strong Raman band at 126 cm(-1) in both molecules is structure-independent non-genuine mode, correlated to lattice vibrations in the solid phase.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP92488	6-Methylcoumarin		92-48-8	Price

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