Knowledge Bank

The microwave spectrum of the partially bound complex (CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$CCN-SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ has been recorded. The nitrogen-sulfur bond length is 2.34 $\backslash AA$, which is almost exactly half way between that in weakly bound N$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$-SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ and the more strongly bonded (CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$N-SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$. A simple Townes and Dailey analysis of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$N nuclear quadrupole coupling constant gives a value of about 0.19 e$\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$ transferred away from the (CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$CCN upon complexation. Ab initio calculations at the MP2/aug-cc-pvtz level yield a binding energy relative to free (CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$CCN and SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ of 11.0 kcal/mol, which is only about a fourth of that of (CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$N-SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$. As noted previously for the complex HCCCN-SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$,} \textbf{212}, 213 (2002).} comparison of the N-S bond length with those of a series of SO$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ 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$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$CCN.