DFT Studies of Rotational Conformers of 4-Azido-N-Phenylmalemide

DFT calculations were performed to study the rotational conformers of 4-Azido-N-Phenylmalemide using B3LYP with 7 basis sets, 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p), and 6-311++G(df,pd). DFT studies show that the two isomers of 4-Azido-N-Phenylmalemide have the same energetics. Furthermore, the rotational barrier between the isomers is 0.17 eV in N, N-dimethylacetamide (NNDMA) and 0.15 eV in tetrahydrofuran (THF). These indicate that the isomers are present in the solvents and can be easily converted between them. The azido asymmetric stretch differs by about 1 cm-1 between the isomers in NNDMA and less than 1 cm-1 in THF. The most significant effect of rotational conformers is in the coupling strength of fermi resonances with the most impact in THF environment. Therefore, the current DFT results show that isomers of 4-Azido-N-Phenylmalemide can be mostly detected in THF by 2D IR technique. Furthermore, the results from seven basis set provide consistent conclusion on the isomers, dependence of the basis sets may be useful information to the development of functionals in DFT method and may be served as a useful tool to understand coupling of vibrational modes of complex molecules and their isomers.