STRUCTURAL STUDY OF METHYL ISONICOTINATE BY GAS-PHASE ELECTRON-DIFFRACTION COMBINED WITH AB-INITIO CALCULATIONS

The molecular structure of methyl isonicotinate was studied by gas pha se electron diffraction combined with ab initio calculations. The mole cular skeleton was assumed to be planar. The determined values of prin cipal structure parameters (r(g) and angle(alpha)) are as follows: r(N -C) = 1.343(5) Angstrom, r(CC)(ring) = 1.401(3) Angstrom, r(C-gamma-C) = 1.499(9) Angstrom, r(C=O) = 1.205(5) Angstrom, r (C(=O)-O) = 1.331( 8) Angstrom, r(O-C-Me) = 1.430(8) Angstrom, (r(C-H)) = 1.103(10) Angst rom, angle CNC = 117.6(9)degrees, LC(beta)C(gamma)C(beta) = 118.7(9)de grees, angle Cbeta,transCgamma-C(=O) = 118.6(12), angle CgammaC=O = 12 1.4(12)degrees, angle CgammaC-O = 114.2(10)degrees, angle COC = 115.4( 15)degrees, where angled brackets denote average values and C-beta tra ns denotes the carbon atom which is trans to the carbonyl oxygen atom. Values in parentheses are the estimated limits of error (3 sigma) ref erring to the last significant digit. The structure of the ring in met hyl isonicotinate agrees with that of pyridine within experimental err or. In contrast, the structure parameters of the COOCH3 group are sign ificantly different from those of methyl acrylate and methyl acetate. These differences have been discussed in terms of hyperconjugation and steric effects.