Negative Hyperconjugation versus Electronegativity: Vibrational Spectra of Free Fluorinated Alkoxide Ions in the Gas Phase

Jos Oomens; Giel Berden; Thomas Hellman Morton

doi:10.1002/cphc.201500177

Negative Hyperconjugation versus Electronegativity: Vibrational Spectra of Free Fluorinated Alkoxide Ions in the Gas Phase

Chemphyschem. 2015 Jun 22;16(9):1992-5. doi: 10.1002/cphc.201500177. Epub 2015 Apr 17.

Authors

Jos Oomens^{1

2}, Giel Berden¹, Thomas Hellman Morton³

Affiliations

¹ Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen (The Netherlands).
² van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098XH Amsterdam (The Netherlands).
³ Department of Chemistry, University of California, Riverside, Riverside, CA 92521-0403 (USA). morton@citrus.ucr.edu.

PMID: 25891438
DOI: 10.1002/cphc.201500177

Abstract

CO stretching frequencies of free, gaseous, fluorinated alkoxide ions shift substantially to the blue, relative to those of corresponding alcohols complexed with ammonia. Free α-fluorinated ions, pentafluoroethoxide and heptafluoroisopropoxide anions, display further blue shifts relative to cases with only β-fluorination, providing experimental evidence for fluorine negative hyperconjugation. DFT analysis with the atoms in molecules (AIM) method confirms an increase in CO bond order for the α-fluorinated ions, demonstrating an increase in carbonyl character for the free ions.

Keywords: difluorocarbene; electron detachment; infrared multiple photon dissociation; ion cyclotron resonance; photolysis.