Interactions and reactions in some 2,2'-disubstituted biphenyls--an open or shut case.

2-Dimethylaminobiphenyls bearing an electron deficient alkene in the 2' position show either Me2N...C=C interactions (2.941-2.976 A) or form a new N-C bond (1.586-1.604 A) to give a zwitterion. The former provides a model for an intermolecular interaction, while the latter provides structural information on organic anionic systems uncoordinated by metal cations.

Weak attractive interactions between methylthio groups and electron-deficient alkenes in peri-naphthalenes: a competition with conjugative effects.

The solid-state conformations of five peri-disubstituted naphthalenes bearing a methylthio group and an electron-deficient alkene indicate a weak attractive interaction between the functional groups in four cases in which out-of-plane displacements lead to a common orientation of the MeSsp(2)-C vector to the alkene bond. In some cases the interaction is not strong enough to outweigh the tendency of the alkene to conjugate with the aromatic ring, and in one case this optimisation of conjugation alone controls the molecular conformation. The methylthio group lies close to the aromatic plane in all but one example for which the plane of the sulfide group is presented to the alkene.

Structural studies of peri-interactions and bond formation between electron-rich atomic centres and N-phenylcarboxamides or nitroalkenyl groups.

Structural studies of peri-interactions with dimethylamino groups in naphthalene systems indicate that the N-phenylcarboxamide group has a through-space electron attracting power closer to that of a carboxylic ester than a N,N-dialkylcarboxamide, while 2-nitroalkenyl groups have a lower through-space electron attracting power. However, addition of a benzoyl group to the 2-position of the nitroethenyl group leads to cyclisation to give a zwitterion, in which the carbanion is stabilised by full conjugation with the nitro group and partial conjugation with the carbonyl group. An interesting case where a steric interaction overrides an electrophile/nucleophile attraction is also described. The limitations to the interpretation of short contact distances from crystallographic measurements are discussed.