MATRIX ISOLATION STUDIES OF WEAK HYDROGEN BONDING: ALKYNE COMPLEXES
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Date
1990
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Ohio State University
Abstract
The matrix isolation technique has been combined with infrared spectroscopy for the isolation and characterization of weakly hydrogen bonded molecular complexes. The systems studied all employed the C-H group as the proton donor in the complex. A series of alkynes were codeposited with lone electron pair donors containing N, O, S, P, Se and As donor atoms into argon matrices. Distinct evidence of hydrogen bond formation was observed, primarly through a red shift of the C-H stretching mode and a blue shift of the CCH bending mode. Perturbation to the triple bond stretch of the alkyne was also noted, leading to a small red shift. The C-H stretching mode shifted between 50 and $300 cm^{-1}$, depending on the base and on the substituents on the alkyne. The observed shifts correlated well with the proton affinities of the base and the Hammett substltuent constants for the alkyne substituents. Recent studies have extended these complexes to alkenes, where hydrogen bond formation was again observed, but with significantly smaller shifts. Most recently, the interaction of anions, particularly F-, with alkynes has been examined. Here much larger shifts were observed, in keeping with the very strongly basic nature of the fluoride anion
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Author Institution: Departmetn of Chemistry, University of Cincinnati