Knowledge Bank

A pulsed beam Fourier transform microwave spectrometer was used to investigate the rotational spectrum of 1,2-dithiin, a six-membered cyclic disulfide having the structure, CH=CH-S-S-CH=CH. This compound is thermally unstable and is sensitive to oxygen and light. A fit of observed a type transitions to a Watson Hamiltonian gives the following rotational constants for the normal isotopic species: A = 3326.3621 (18) MHz, B = 3102.4821(18) MHz and C = 1756.0027(7) MHz. Both the observation of nuclear spin statistical weights and the absence of b and c - type transitions at the frequencies calculated from the a- type fit show that the ring has a twisted conformation with $C2$ molecular symmetry. Spectral assignments of the singly-substituted $\mathrm{<mrow\; data-mjx-texclass="ORD">34</mrow>}S$ and two $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ isotopomers were obtained in natural abundance, providing isotopic moments of inertia for the determination of the $rs$ structural ring parameters listed below: $r(S-S)=2.052(3)\backslash AA,r(C-S)=1.759(4)\backslash AA,r(C=C)=1.353(3)\backslash AA,r(C-C)=1.451(4)\backslash AA,\theta (SSC)=98.7(2)\circ ,\theta (SCC)=121.4(2)\circ ,\theta (CCC)=124.2(2)\circ ,\varphi (SSCC)=41.2\circ ,\varphi (SSCC)=-0.3\circ ,\varphi (CCCC)=29.0\circ and\varphi (CSSC)=53.9\circ$.