Hinderungspotential der internen Rotation, Dipolmoment und Quadrupolkopplungskonstanten aus dem Mikrowellenspektrum des 4-Methyl-Pyridins

Abstract

The microwave rotational spectrum of 4-methyl-pyridine (γ-picoline) has been investigated in the region from 8 to 37 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 n; | m |=3 n. From low-/ lines m=0 (a-type transitions) the rotational constants A′ (less methyl top) =6 082.145, B=2 524.850, C=1 783.991 MHz, the dipole moment μα=2.70 D, and the nuclear quadrupole coupling constants for the 14N nucleus χaa= —4.82, χbb—χcc= —2.8 MHz have been determined. From the wide splitting of the lines | m | = 3, | K | = 1 the potential barrier has been derived as V6=13.51 cal/mole, a value which is very close to those previously deduced for toluene and para-substituted toluenes.