Knowledge Bank

Simultaneous deposition of $CH2ClX$ (X = F, Cl, Br, I) with atomic lithium or sodium at high dilution in argon on a CsI window maintained at $15\circ K$ has produced the monochloromethyl free radical for infrared spectroscopic study. Vibrational assignments to $\nu 2$ (the symmetric C-Cl stretch), $\nu 3$ (the symmetric valance angle bend) and $\nu c$ (the out of plane hydrogen bend) are supported by the reactions of lithium with $CHDCl2$ and lithium or sodium with $CD2Cl2$. These assignments are further substantiated by normal coordinate calculations. The unusually high C-Cl force constant in $CH2Cl$ (4.09=0.03 mdyn/\AA) indicates considerable stabilization of the C-Cl bond. Therefore, we suggest (p-p)$\pi$ bonding in $CH2Cl$. The average calculated $F\alpha$ does not quantitatively account for the observed isotopic frequencies of $v6$. However, a simple harmonicquartic potential function obtained from first order perturbation theory (V(O) = (1/2(1.83) ($\Delta$(O)$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}+(10.7)(\Delta$O)$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$)$\times 10-13$ ergs) accurately determines the observed spectrum: this large positive quartic term is evidence for a planar radical.