Structural (X-ray), spectral (FT-IR and Raman) and quantum chemical investigations of a series of 6-benzylaminopurine derivatives

The structural and spectroscopic properties of 6-(2-methylbenzylamino)purine 1, 6-(4-methylbenzylamino)purine 2, 6-(3,4-dimethoxybenzylamino)purine 3, 2-chloro-6-(3-bromobenzylamino)-9-isopropylpurine 4 and 2-chloro-6-(3,4-dichlorobenzylamino)-9-isopropylpurine 5 have been investigated by means of single crystal X-ray diffraction analysis, FT-IR and Raman spectroscopy, and quantum chemical calculations, where HF, DFT, RI-MP2 and MP2 methods in combination with the cc-pVDZ basis set have been used. The theoretically obtained structural as well as spectral parameters have been compared with those experimentally obtained. One of the unusual structural features is the finding that the electroneutral form of 6-(2-methylbenzylamino)purine 1 is protonated at the N7 position of the purine ring, which is not a typical protonation site for N9-unsubstituted adenine derivatives.