Chemical shift tensors in isomers of adenine: relation to aromaticity of purine rings?

Abstract

The (13)C and (15)N chemical shift tensors are measured, calculated, and compared for three N-benzyladenine isomers with an attempt to characterize differences in electron distribution in the purine ring related to the position of the substituent. Furthermore, the aromaticity of the purine rings is evaluated on the basis of nucleus-independent chemical shifts, and variations among the isomers are discussed. Both parameters indicate significant differences between the electronic properties of the N3-substituted compound and the N7/N9 pair of structures, which can be viewed more generally as the reason for the different stabilities of the individual tautomers.