Sulfoxides pyramidal structure

Due to the high rate of reaction observed by Meissner and coworkers it is unlikely that the reaction of OH with DMSO is a direct abstraction of a hydrogen atom. Gilbert and colleagues proposed a sequence of four reactions (equations 20-23) to explain the formation of both CH3 and CH3S02 radicals in the reaction of OH radicals with aqueous DMSO. The reaction mechanism started with addition of OH radical to the sulfur atom [they revised the rate constant of Meissner and coworkers to 7 X 10 M s according to a revision in the hexacyanoferrate(II) standard]. The S atom in sulfoxides is known to be at the center of a pyramidal structure with the free electron pair pointing toward one of the corners which provides an easy access for the electrophilic OH radical. 

The structural determination of diphenyl sulfoxide has also been performed (4), ahd shows that this diaryl sulfoxide also has an approximately pyramidal structure. The S—O bond length in this molecule is reported as 1.47 A, again suggesting some double-bond character. 

In the absence of detailed product analysis, and of readily observable intermediate species in our experiments, we can merely say that our results are consistent with the conclusions of other more detailed studies (5.17.20) of the reaction mechansims of these compounds. Thus it is reasonable that dimethyl sulfoxide, having its S-atom at the centre of a pyramidal structure with a free electron pair pointing to one corner, is readily acessible to electrophilic attack by the OH radical. There is in fact conductometric evidence (20) for the... 

Recently, the X-ray analysis of 3,4-bis(methylthio)-l,2,5-thiadiazole 1-oxide demonstrated that the oxidized form of the ring is essentially non-aromatic and shows a pyramidal sulfoxide structure. Interaction between the sulfur lone pair of electrons and the diene is small, the C(3)—C(4) bond length lying closer to that of cyclopentadiene than of thiophene or (3). Theoretical calculations indicate that aromaticity effects lower the inversion barrier nearly equally in the thiophene and thiadiazole 1-oxides by stabilizing the planar transition state and destabilizing the pyramidal structure (82JA1375). 

The SH group induces much smaller shift changes. The CH2 resonance of carbons adjacent to a thiol group appear around 24-35 ppm according to the presence of other substituents and chain branching. Similar effects are seen in thioethers. Sulfoxides of the type RR SO are chiral because of the pyramidal structure of the sulfoxide group and hence nonequivalence can be seen in the NMR spectra. Methylene carbons adjacent to sulfone groups appear around 55-65 ppm. 

Examine both pyramidal and planar forms for each of the above molecules amine, phosphine and sulfoxide). Assume that the lower and higher-energy forms con-espond, respectively, to the preferred molecular structure and the transition state for configuration inversion. 

The molecular structure of dimethyl sulfoxide has been determined both in the gas phase and in the solid state (Table II). The bond angles suggest that the molecule is approximately pyramidal, with sulfur at the apex. The distortions from the expected pyramidal bond angles are... 

Sulfoxides possess a non-planar pyramidal configuration consequently, chiral sulfoxides can exist as optical enantiomers (see Chapter 5, p. 63). This is illustrated by the structures (33a) and (33b) showing the optical isomers of ethyl methyl sulfoxide (Figure 2). 

Dimethyl sulfoxide (DMSO) has been used as an anti-inflammatory mb for racehorses. DMSO and acetone seem to have similar structures, but the C=0 carbon atom in acetone is planar, while the S=0 sulfur atom in DMSO is pyramidal. Draw correct Lewis structures for DMSO and acetone, predict the hybridizations, and explain these observations. 

This result can be explained in terms of a preference for the carbanion structure in which the carbanion is pyramidal with the electron pair anti to the sulfoxide oxygen. Protonation of such carbanions is highly stereoselective and occurs with retention of configuration. 

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