The noncovalent interaction between sulfur atoms and lone pair donors was quantified through theoretical studies on the alkaloid natural products polycarpathiamine A, polycarpathiamine B, 3-dimethylamino-5-benzoyl-1,2,4-thiadiazole, and dendrodoine. Iterative geometry optimizations performed at the M06-2X/6-31+G(d,p) level revealed the presence of a sulfur���oxygen interaction in each compound's lowest energy conformation. The conformation involving the sulfur���oxygen interaction was favored by on average 4 kcal/mol over the flipped conformation. NMR chemical shifts of the lowest energy conformation calculated using the GIAO method in DMSO most closely matched the experimental NMR chemical shifts. NBO calculations identified the sulfur���oxygen interaction as weak but attractive, with an average energy of 1 kcal/mol. This result indicates that stable energy conformations are dependent upon multiple donor-acceptor orbital interactions, of which the sulfur���lone pair interaction plays a minor role.

Quantifying the nature of sulfur lone pair interactions

247th National Meeting (2014)

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