Crystal structure of bis-thieno[3,2-c;2′,3′-e]-1,2-dithiin, C₈H₄S₄

Microwave Spectra, Molecular Structure, and Electric Dipole Moment of 1,2-Dithiin

“…A plate separation intensity ratios demonstrate the presence of a C 2 axis in the molecule and offer additional evidence to rule out assignwas calculated from frequency shift measurements of the M J Å 0-0, J Å 1-0 Stark transition of OCS using the reported ment of the observed spectra to the envelope conformation. OCS dipole moment of 2.3856 (10) and SSCH 13 CHCHCH isotopomers were readily observed Samples of 1 were synthesized from 1,4-bis(trimethylsi-in natural abundance using isotopic shifts obtained from the lyl)-1,3-butadiyne using a method reported recently (23).…”

“…Geometries determined from ab initio calculations for pla-Five quartic centrifugal distortion constants were used in the nar (C 2£ symmetry), envelope (C s symmetry), and twisted fit of the observed transition frequencies of the 34 S isoto-(C 2 symmetry) ring conformations (10) were used to predict pomer to a Watson Hamiltonian. The two 13 C assignments the rotational spectra of 1. The calculations give kappa equal have fewer transitions, and were fit to the rotational conto 0.29, 0.40, and 0.77, respectively, for these three configu-stants, D J , D K , and D JK .…”

“…The 1 H and levels using a 6-31G* basis set (10). However, geometry 13 C NMR spectra of 1,2-dithiin and its homologues suggest optimized MNDO and STO-3G ab initio calculations give that the ring structure, 1, rather than the acyclic valence a planar ground state structure for 1 (8). No gas-phase studtautomer (2 in Scheme 1) exists in solution (2)(3)(4)(5).…”

“…Support ies of 1 have been reported, but recent X-ray crystallographic for the cyclic form, 1, also comes from NMR studies and analyses have shown that the 1,2-dithia-3,5-cyclohexadiene calorimetric measurements of substituted 1,2-dithiins (6,7). ring contained in several 1,2-dithiin derivatives is nonplanar A recent MNDO calculation finds 1 to be more stable than with a significant twist about the S{S bond (12)(13)(14)(15)(16)(17). 2 by 42.0 kcal/mole (8).…”

“…Observed nuclear spin statistical weights, an inertial defect of D Å I c 0 I a 0 I b Å 027.00685 uÅ 2 , and zero m b and m c electric dipole components show the molecule has C 2 symmetry which corresponds to a twisted conformation about the S{S bond. Spectral assignments were obtained for the singly substituted 34 S and two 13 C isotopomers in natural abundance. The moments of inertia of the four isotopomers were used to determine the following r s structural ring parameters: r(S{S) Å …”