Computational Studies of the Ground and Excited State Potentials of DMSO and H₂SO:  Relevance to Photostereomutation

Abstract

A computational study on ground and excited states of dimethyl sulfoxide (DMSO) and the hypothetical molecule H 2 SO is reported. Full valence CASSCF/6-311+G(3df,2p) with a multireference perturbation theory correction was used for the latter, while DMSO was examined with an active space that neglected only the CH bonds and an analogous basis set that neglected polarization functions on H. A realistic value of 41.5 kcal/mol was obtained for the ground state pyramidal inversion of sulfur for DMSO, though no directly comparable experimental value is available. Calculations were also carried out on singlet and triplet excited state surfaces of both A′ and A′′ symmetry. Relaxed excited state geometries fairly near the ground state geometry were found, but perhaps more importantly, excited state stationary points were also found in C 2V symmetry. These were the lowest energy of any geometry on their respective surfaces. This leads to the speculation that photochemical stereomutation of alkyl sulfoxides may occur without C-S bond cleavage in a mechanism formally analogous to the photochemical cis-trans isomerization of olefins.

Photoabsorption and photodissociation studies of dimethyl sulphoxide (DMSO) in the 35,000–80,000 cm−1 region using synchrotron radiation

“…It may be noted here that the observed peaks do not match with the reported Rydberg peaks of the CH 3 (CD 3 ) radical [39]. Furthermore, all the features assigned to bands of SO in the present work are well reproduced in the spectra obtained by photodissociation of DMSO-h 6 as well as DMSO-d 6 . This lends weight to our interpretation of these peaks in terms of photoabsorption by the SO radical.…”

“…Isotopic substitution is a valuable tool for confirmation of vibrational assignments as seen from some of our earlier works [8,9]. In this context, it is of interest to examine the VUV photoabsorption spectrum of the deuterated isotopologue DSMO-d 6 , on which we do not find any VUV photoabsorption study reported earlier. In the present work, photoabsorption spectra of DMSO-h 6 and DMSO-d 6 are studied in the region 35,000-80,000 cm À 1 ( $ 4.3-9.9 eV) using SR.…”

“…In this context, it is of interest to examine the VUV photoabsorption spectrum of the deuterated isotopologue DSMO-d 6 , on which we do not find any VUV photoabsorption study reported earlier. In the present work, photoabsorption spectra of DMSO-h 6 and DMSO-d 6 are studied in the region 35,000-80,000 cm À 1 ( $ 4.3-9.9 eV) using SR. Details of the experiments performed and the analysis of the spectra carried out with the help of quantum chemical calculations are presented in this paper.…”

High resolution VUV photoabsorption cross section of dimethyl sulphoxide (CH3)2SO

“…CH 3 + SO [11]. The bond dissociation energy for the C-S bond is of the order of 2.3 eV (540 nm) [12] meaning that any of the excited states analyzed here contain enough energy to cleave one of these bonds leading to formation of DMSO products CH 3 SO Å þ CH Å 3 . Amaral and co-workers [11] studied the dissociation of DMSO-d 6 at 210 nm using REMPI-TOFMS (resonance enhanced multi-photon ionisation time of flight mass spectrometry).…”

The nature of the SO bond of chlorinated sulfur–oxygen compounds

“…For reference, the a 1 D state of SO, which contains a r and a p bond, is bound by 103.2 kcal/ mol. The transition state for inversion is 40.1 kcal/mol higher in energy than the minimum-similar to many other XYSO molecules where X and Y are not bonded together via rings [2,[53][54][55][56][57]. The equilibrium geometry of Cl 2 SO leads to two questions.…”