The vibrational and NMR spectra, conformations and ab initio calculations of methoxymethylene- and 1-methoxyethylidene- propanedinitrile

Abstract

The IR and Raman spectra of methoxymethylene-propanedinitrile [H 3COCHC(CN) 2] and 1-methoxyethylidene-propanedinitrile [H 3COC(CH 3)C(CN) 2] as a solid, liquid and solute in various solvents have been recorded in the region 4000-50 cm −1. NMR spectra of both compounds in various solvents at different temperatures were also obtained. Semiempirical (AM1, PM3, MNDO, MINDO3), ab initio using DZP basis sets and DFT calculations using B3LYP with 6-31G∗∗ basis sets were carried out for both compounds. These calculations support the idea on the existence of two conformers with a planar CCOC moiety and with the methyl group oriented as anti and syn towards the CC double bond. The calculated small energy difference between them suggests the presence of both in the samples at room temperature. In contrast with the calculations, only one conformer has been found in the liquid vibrational and NMR spectra. Complete assignments of the vibrational spectra for the compounds mentioned were made with the aid of normal coordinate calculations employing scaled ab initio and DFT force field constants. The scaled ab initio and DFT frequencies indicate that the conformer present in the liquid (solutions) and solid phases is anti.