MICROWAVE AND AB INITIO STUDY OF (CH$_{3}$)$_{3}$CCN-SO$_{3}$
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Date
2006
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Ohio State University
Abstract
The microwave spectrum of the partially bound complex (CH$_{3}$)$_{3}$CCN-SO$_{3}$ has been recorded. The nitrogen-sulfur bond length is 2.34 $\AA$, which is almost exactly half way between that in weakly bound N$_{2}$-SO$_{3}$ and the more strongly bonded (CH$_{3}$)$_{3}$N-SO$_{3}$. A simple Townes and Dailey analysis of the $^{1}$$^{4}$N nuclear quadrupole coupling constant gives a value of about 0.19 e$^{-}$ transferred away from the (CH$_{3}$)$_{3}$CCN upon complexation. Ab initio calculations at the MP2/aug-cc-pvtz level yield a binding energy relative to free (CH$_{3}$)$_{3}$CCN and SO$_{3}$ of 11.0 kcal/mol, which is only about a fourth of that of (CH$_{3}$)$_{3}$N-SO$_{3}$. As noted previously for the complex HCCCN-SO$_{3}$,} \textbf{212}, 213 (2002).} comparison of the N-S bond length with those of a series of SO$_{3}$ adducts indicates that the proton affinity Lewis base is a good predictor of the properties of the complex. Indeed, spectra of this adduct were readily located on the basis of the proton affinity value for (CH$_{3}$)$_{3}$CCN.
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Author Institution: Department of Chemistry, University of Minnesota, 207 Pleasant St., SE, Minneapolis, MN 55455