Knowledge Bank

The pure rotational spectra of the normal and benzene-$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C species of the benzene-trifluoromethane complex have been measured using molecular beam Fourier transform microwave spectroscopy. The normal species is a symmetric top, with the symmetry axes, C$3$ of CHF$3$ and C$6$ of benzene, lying along the same line. The rotational spectrum of the benzene-$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C isotopomer is that of a slightly asymmetric top. Both species are characterized by an almost free rotation of the two subunits with respect to each other. From the present data the calculated length of the C-H$\cdots \pi$ hydrogen bond is 2.366(2) \AA. The analysis of the structural and energetic features of the C-H$\cdots \pi$ interaction allow us to classify it as a weak hydrogen bond.