Molecular orbital calculations for conjugated molecules containing boron and nitrogen

The Π-electron networks in boron–nitrogen chains and rings have been treated by l.c.a.o.–m.o. techniques. The results for B—N chains predict a very weak alternation of bond order, smaller charges on the terminal atoms than on the internal atoms, and very little conjugation across B—B and N—N linkages. The calculations for the B—N rings predict an absence of a "4n + 2" pi-electron rule for aromaticity and a predominance of exocyclic over endocyclic Π bonding in the substituted rings. These results are compared with the properties of known B—N chains and rings and are contrasted with l.c.a.o.–m.o. calculations for the analogous carbon–carbon systems.