Blue shifted intramolecular C−H···O improper hydrogen bonds in conformers of zidovudine

Blue shifted C–H stretch vibrations caused by C–H···O intramolecular improper hydrogen bonds in zidovudine (or AZT) conformers are employed to differentiate its conformers. Two sugar–sugar C–H···O(5′) improper hydrogen bonds, existing in conformers of AZT with apparent drug potency, are related to their unique sugar puckering, showing C(3′)-exo or -endo orientations. Aqueous solution causes a global red shift in IR spectra, but remains reduced blue shifted C–H stretch frequencies. Molecular electrostatic potentials (MEPs) of the conformers and orbitals such as 40a of AZT-B and 37a of AZT-C, which are found to be responsible for the intramolecular improper hydrogen bonds, are also given in this study.