Conformational and stereoelectronic investigation of chloromethyl methyl sulfide and its sulfinyl and sulfonyl analogs

The rotational equilibria of some sulfur-containing model compounds were theoretically determined, and a rationalization of the effects responsible for the results obtained is given. Experimental approaches, namely NMR and infrared, were also used to show the gauche (ClCSCH3 fragment) prevalence for these compounds and allowed us to elucidate the orbital interactions involved in such systems. The gauche rotamer of the sulfide is about 3.2 kcal mol−1 more stable than anti in the gas phase. For the sulfinyl derivative the relative energies for the most stable rotamers are 0.0, 1.0 and 1.7 kcal mol−1, corresponding to gauche-1 (CCl antiperiplanar to SO), gauche-2 (CCl antiperiplanar to lone pair) and anti. The calculated energy difference (anti-gauche) between the sulfonyl rotamers is 2.6 kcal mol−1. Natural bond orbital analysis indicated that the anomeric effect (nS→σCCl∗) plays the main role in stabilization of gauche in the sulfide compound, and that other important hyperconjugative interactions also occur for the remaining compounds.