The vibrational spectra of 1,3-dithiane-1-oxide and 1,3-dithia-1- oxocyclohept-5-ene

Abstract

The IR spectra of 1,3-dithiane-1-oxide (I) and 1,3-dithia-1-oxocyclohept-5- ene (II) were recorded in solution, solid and liquid phase over 4000-400 cm -1 spectral range. It was found that both (I) and (II) in liquid phase and solutions exist in two conformations: (I) chair-e (Ce) and chair-a (Ca) with equatorial and axial positions of the SO bond, respectively, and (II) chair-e (Ce) and boat-e (Be). The intensity variations with temperature (300-180 K) of the bands 632 (C a) and 644 cm-1 (Ce) of (I) in acetone-d 6 and the bands 482 (Be) 448 cm-1 (C e) of (II) in melt were employed in Van't Hoff plot and gave the values ΔH°(Ca - Ce) = 380 ± 40 cal mol-1 (I) and ΔH° (Be - Ce) = 400 ± 100 cal mol-1 (II). Ab initio calculations were carried out with the Gaussian 98 program using the basis set 6-31G(d) for (I) and 6-311++G(d,p) for (II). The energy difference between Ca and C e conformations for (I) and Be and Ce for (II) are in a good agreement with experimental results. Vibrational frequencies for both conformations (I) and (II) were calculated. After appropriate scaling a reasonably good agreement between the experimental and calculated wave numbers was obtained. © 2010 Elsevier B.V.