Low-Frequency CH Stretch Vibrations of Free Alkoxide Ions
Jos Oomens1,2, Giel Berden1, Thomas Hellman Morton3
1Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED, Nijmegen, The Netherlands.
Abstract:
CH stretches in hydrocarbon cations often shift to lower frequencies relative to neutral molecules, because they do not have sufficient electrons to give every bond an electron pair. A parallel effect in negatively charged species has not been previously observed. Here we show that CH bond weakening occurs in alkoxide anions as a consequence of hyperconjugation. The reasoning differs somewhat from the case of positively charged ions, but the net effect is the same: to lower CH stretching frequencies by hundreds of wavenumbers.
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