Abstract
In the present communication, quantitative interpretation and assignments of the electronic absorption spectra, vibrational and one- and two-dimensional NMR spectra of alloxan, are detailed. A synergic analysis based on DFT and TD-DFT calculations and the experimental findings are performed. Attempt is made to relate these spectral findings to the electronic structure of alloxan. The computed electronic spectrum predicted three well defined bands. Natural transition orbital analysis indicate an intramolecular charge transfer from n(p pi) orbital of the water oxygen atom resulting in the short wavelength n pi* at 200 nm. Furthermore, UV-photoabsorption cross section for alloxan and its monohydrate are simulated. The spectrum, composed of 10 excited states, was simulated with the nuclear ensemble approximation, sampling a Wigner distribution with 300 points. The FT-IR spectrum of alloxan, measured in the solid state as KBr pellets is reported and is computed at the DFT/B3LYP/6-311+-FG** level of theory. All observed vibrations are assigned. The 600 MHz one- and two-dimensional COSY, H-1 NMR spectra of alloxan, measured in DMSO, are reported and analyzed and computed theoretically using the CIAO method. Hydrogen-bond interactions are responsible for remarkable downfield shift of H-1 NMR peaks for alloxan. (C) 2016 Elsevier B.V. All rights reserved.