An investigation into the relaxation of the conformers of butan-2-ol in a supersonic expansion

Abstract

The behavior of the chiral secondary alcohol butan-2-ol in both helium and argon-based supersonic expansions has been investigated by a combination of high-resolution microwave spectroscopy and ab initio molecular structure calculations. The study extends and complements a previous investigation that concentrated solely on an argon-based expansion. The spectrum of the helium-based expansion has been shown to contain at least six conformers of butan-2-ol, indicating a marked difference from the spectrum of the argon-based system, which has been shown to consist of contributions from only three. This indicates a difference in the relative abilities of the two gases to produce efficient conformer relaxation. By consideration of the calculated barriers to inter-conversion between the various conformers, we are able to show that this behavior is qualitatively consistent with previous observations of similar systems and a few remarks regarding the likely cause of this behavior are also made. Finally, we have been able to identify and characterize the four 13C isotopomers of the lowest energy butan-2-ol conformer and to perform a Kraitchmann-type analysis to confirm the conformation of the carbon chain in this species.