Hydrogen delocalization in an asymmetric biomolecule: The curious case of alpha-fenchol

Type of content
Journal Article
Thesis discipline
Degree name
Publisher
MDPI AG
Journal Title
Journal ISSN
Volume Title
Language
eng
Date
2022
Authors
Medel R
Springborn JR
Suhm MA
Crittenden, Deborah
Abstract

Rotational microwave jet spectroscopy studies of the monoterpenol α-fenchol have so far failed to identify its second most stable torsional conformer, despite computational predictions that it is only very slightly higher in energy than the global minimum. Vibrational FTIR and Raman jet spectroscopy investigations reveal unusually complex OH and OD stretching spectra compared to other alcohols. Via modeling of the torsional states, observed spectral splittings are explained by delocalization of the hydroxy hydrogen atom through quantum tunneling between the two non-equivalent but accidentally near-degenerate conformers separated by a low and narrow barrier. The energy differences between the torsional states are determined to be only 16(1) and 7(1) cm−1 hc for the protiated and deuterated alcohol, respectively, which further shrink to 9(1) and 3(1) cm−1 hc upon OH or OD stretch excitation. Comparisons are made with the more strongly asymmetric monoterpenols borneol and isopinocampheol as well as with the symmetric, rapidly tunneling propargyl alcohol. In addition, the third—in contrast localized—torsional conformer and the most stable dimer are assigned for α-fenchol, as well as the two most stable dimers for propargyl alcohol.

Description
Citation
Medel R, Springborn JR, Crittenden DL, Suhm MA (2022). Hydrogen delocalization in an asymmetric biomolecule: The curious case of alpha-fenchol. Molecules. 27(1). 101-.
Keywords
delocalization, tunneling, terpene, alcohol, vibrational spectroscopy, supersonic jet expansion, structural determination
Ngā upoko tukutuku/Māori subject headings
ANZSRC fields of research
Fields of Research::34 - Chemical sciences::3404 - Medicinal and biomolecular chemistry::340402 - Biomolecular modelling and design
Fields of Research::34 - Chemical sciences::3407 - Theoretical and computational chemistry::340704 - Theoretical quantum chemistry
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