Chemical Insights from High-Resolution X-ray Photoelectron Spectroscopy and ab Initio Theory: Propyne, Trifluoropropyne, and Ethynylsulfur Pentafluoride

Authors

Leif J. Sæthre, University of Bergen
Nora Berrah, Western Michigan University
John D. Bozek, University of California - Berkeley
Knut J. Borve, University of Bergen
Thomas X. Carroll, Keuka College
Edwin Kukk, Western Michigan University
Gary L. Gard, Portland State University
Rolf Winter, Portland State University
T. Darrah Thomas, Oregon State UniversityFollow

Date of this Version

2001

Comments

Published in J. Am. Chem. Soc. No. 123, 10729-10737, 2001.

Abstract

High-resolution carbon 1s photoelectron spectroscopy of propyne (HC=CH₃) shows a spectrum in which the contributions from the three chemically inequivalent carbons are clearly resolved and marked by distinct vibrational structure. This structure is well accounted for by ab initio theory. For 3,3,3-trifluoropropyne (HC=CF₃) and ethynylsulfur pentafluoride (HC=SF₅), the ethynyl carbons show only a broad structure and have energies that differ only slightly from one another. The core-ionization energies can be qualitatively understood in terms of conventional resonance structures; the vibrational broadening for the fluorinated compounds can be understood in terms of the effects of the electronegative fluorines on the charge distribution. Combining the experimental results with gas-phase acidities and with ab initio calculations provides insights into the effects of initial-state charge distribution and final-state charge redistribution on ionization energies and acidities. In particular, these considerations make it possible to understand the apparent paradox that SF₅ and CF₃ have much larger electronegativity effects on acidity than they have on carbon 1s ionization energies.