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

Abstract

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.

Effects of the Intramolecular Group and Solvent on Vibrational Coupling Modes and Strengths of Fermi Resonances in Aryl Azides: A DFT Study of 4-Azidotoluene and 4-Azido-N-phenylmaleimide

“…While 4azidotoluene is a rigid organic small molecule and can be built uniquely in GaussView, there are two 4-azido-Nphenylmaleimide rotational conformers and they have very similar IR spectra. 69 In this work, we report and discuss only one conformer shown in Figure 1. This conformer is energetically the same as the second conformer.…”

“…This conformer is energetically the same as the second conformer. 69 For organic small molecules of larger size, many conformers may coexist and molecular dynamics simulations may be needed to ensure proper sampling of the conformational configuration. 70 Three types of DFT calculations were performed for each molecule in a specific solvent environment, namely, geometry optimizations, harmonic frequency calculations, and anharmonic frequency calculations.…”

“…The two molecules were built using GaussView6 that interfaces with Gaussian 16 software. While 4-azidotoluene is a rigid organic small molecule and can be built uniquely in GaussView, there are two 4-azido- N -phenylmaleimide rotational conformers and they have very similar IR spectra . In this work, we report and discuss only one conformer shown in Figure .…”

“…In this work, we report and discuss only one conformer shown in Figure . This conformer is energetically the same as the second conformer . For organic small molecules of larger size, many conformers may coexist and molecular dynamics simulations may be needed to ensure proper sampling of the conformational configuration …”