Supersonic jet studies of alkyl-substituted pyrazines and pyridines. Minimum-energy conformations and torsional motion

Conformational perferences for methyl-, ethyl-, propyl-, and isopropyl-substituted pyrazines and pyridines are determined by mass resolved excitation spectroscopy (MRES) and MOPAC 5/PM3 semiempirical calculations. The results of these studies suggest that the conformational behavior of alkyl-substituted pyrazines and pyridines is different from that of alkyl-susbtituted benzenes. Based on the experimental and semiempirical theoretical results reported herein and published ab initio calculations, this difference can be attributed to a stabilizing interaction between an α-hydrogen atom of the alkyl substituent and the adjacent lone pair nonbonding electrons on the ring nitrogen atom