Determination of the Minimum Energy Conformation of Alkyl Substituted Pyrazines
Abstract
Supersonic jet laser spectroscopy has been utilized to identify the minimum energy conformers of substituted aromatic molecules in the gas phase. These determinations have been performed based on the observation that each conformer produces its own origin transition for the excitation. Thus the counting of origin transition in the mass resolved excitation spectrum reveals the number of conformers present for a given system. Conformational preferences for methyl, ethyl, isopropyl and n-propyl substituted pyrazines are determined by mass resolved excitation spectroscopy for the supersonic jet cooled molecules and MOPAC 5.0 semiempirical conformational calculations. The results of these studies suggest that the behavior of the alkyl substituted pyrazines is very different from that of alkyl substituted benzenes. This difference is caused by substantial hydrogen bonding between the alpha-hydrogens of the alkyl substituent and the adjacent lone pair nonbonding electrons on the ring nitrogen atom. One of these hydrogen atoms becomes nearly planar (ca. approx 10 according to the MOPAC 5.0 calculations) with the aromatic ring. (AW)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 15, 1989
- Accession Number
- ADA216974
Entities
People
- Elliot R. Bernstein
- Hoong-sun Im
- J. I. Seeman
Organizations
- Colorado State University