Microwave spectrum, barrier to internal rotation and dipole moment in 5-methyl-pyrimidine

Abstract

The microwave rotational spectrum of 5-methyl-pyrimidine has been investigated in the region from 8 to 27 GHz, the three types of lines to be expected for a molecule of this symmetry and with a very low sixfold barrier hindering internal rotation of the methyl top have been found: m = 0; | m| ≠ 0,3; | m| = 3 n. From the m = 0 (a-type transitions) the rotational constants A′ (less methyl top) = 6108.41, B = 2642.198, C = 1844.196 MHz and the dipole moment μ = 2.881D have been determined. From the wide splitting of the lines | m| = 3, | k| = 1 the potential barrier has been derived as V 6 = 11.73 cal/mole.