N-NITROSOTHIALDINE. SYNTHESIS, X-RAY CRYSTALLOGRAPHY, AND N-N ROTATIONAL BARRIER

Article abstract of DOI:10.1016/0040-4020(81)85004-1

Crystalline N-nitrosothialdine (2) has been prepared in 38percent yield by treating thialdine (1) with n-butyl nitrite and acetic acid in hexane.X-Ray crystallography of 2 revealed that its three methyl groups are all cis and, rather surprisingly, all equatorial; this finding contrasts sharply with results for other nitrosamine heterocycles which have been investigated, whose bulky alpha substituents are forced into a primarily axial orientation by the large steric requirement of the N-N-O system.The equatorial methyl group both displaces the nitroso group from the C-N-C plane and twists it somewhat about the N-N bond.N-Nitrosothialdine's unusually low barrier to rotation about the N-N bond (72 kJ/mole) is attributed to this steric crowding, combined with inductive electron withdrawal by the two sulfur atoms.