Homoallylic interaction between a nitrogen lone pair and a non-adjacent π-bond. Part 6. Nature of the lone-pair electrons in n,π-homoconjugated aliphatic amines

Abstract

In order to elucidate the nature of the lone-pair electrons involved in the n,π-homoconjugative system, u.v. absorption spectra have been obtained for several cyclic and bicyclic amines containing a non-adjacent benzene ring. The spectra of bishomobenzylic n,π-interacting systems (1,2,3,4-tetrahydro-1,4-iminonaphthalene derivatives) are different from those of homobenzylic systems (1,2,3,4-tetrahydroisoquinoline derivatives). We have also studied the charge-transfer complexes of iodine with various cyclic and bicyclic amines containing non-adjacent π-groups and shown that iodine–amine charge-transfer absorption is a useful means of assigning the n-orbital ionizations in the photoelectron spectra of amines. Differences in the nature of the lone-pair electrons between bishomoallylic and homoallylic n,π-interacting systems and between bishomobenzylic and homobenzylic n,π-interacting systems are discussed in relation to homoconjugation.