Conformational stabilities, rotational barriers, and vibrational spectra of 2-pyrrolecarboxaldehyde and 3-pyrrolecarboxaldehyde calculated using density functional theory

Abstract

Conformational stabilities, molecular structures, and vibrational frequencies of 2 and 3-pyrrole­carboxaldehyde are investigated using the density functional theory at the B3LYP/6-311++G** level of theory. From the computations, cis-2-pyrrolecarboxaldehyde is 3.57 kcal/mol thermodynamically more preferable than trans-2-pyrrolecarboxaldehde, and trans-3-pyrrolecarboxal­dehyde is found to be more preferable than their cis conformer with an energy difference of 0.30 kcal/mol. The computed geometrical parameters are in agreement with the available experimental data. The effect of solvents on the conformational stability of both 2- and 3-pyrrole­carboxaldehydes in nine different solvents are investigated using the polarizable continuum model. The highest occupied and lowest unoccupied molecular orbitals, infrared vibrational wavenumbers and intensities, and molecular electrostatic potentials are reported. Reliable vibrational assignments are proposed based on the potential energy distribution using the VEDA4 program. The simulated vibrational IR spectra are plotted and compared with the available experimental FT-IR spectrum.