Effect of ring size on the basicity and kinetic behaviour of 1,5-dimethylnaphtho[1,8-bc]-1,5-diazacycloalkanes

Abstract

The basicities and rates of proton transfer for a series of 1,5-diemthylnaphtho[1,8-bc]-1,5-diazacycloalkanes (2)–(5) are compared with data for 1,8-bis(dimethylamino)naphthalene (1). For amines (2) and (3) with smaller rings, the rates of proton transfer are higher and the basicities are lower than for (1). For (2), the results are not very different from those expected for a simple aromatic amine. With larger rings, as in (4) and (5), the rates of proton transfer are lowr and the basicities are higher than for (1). The results can be explained on the basis that with smaller and less flexible rings, the conformations of the amine and protonated amine are similar and there is little difference in strain between the two. For larger rings the protonated amine can adopt a conformation with an intramolecular hydrogen bond and in this conformation there is much less strain than in the amine. The basicity and rates for 1,8-dipyrrolidinonaphthalene (6) are also considered.