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In this work, the structural conformation of pyrrole-2-carboxaldehyde was evaluated using potential energy surface (PES) scan employing DFT computations using B3LYP method with 6-311++G(d,p) level of basis set. The molecule assumed cis form in conformational ground state being more stable than the trans by 15.21 kJ mol−1 due to the orientation of the N–C–C = O dihedral angle. Existence of hydrogen bonds due to intra- and inter-molecular interactions was envisaged. The geometrical parameters of optimized monomeric and dimeric forms have been computed. The computational structural parameters of monomer are in good agreement with its experimental counterparts. The HOMO-LUMO energies were employed for determination of chemical reactivity descriptors. The electronic properties such as frontier molecular orbitals and Global reactivity descriptors were predicted using TD-DFT method. The local reactivity descriptors such as Fukui functions were investigated to determine the electrophilic and nucleophilic attacks within the molecule. The calculated first order hyperpolarizability value exhibited its suitability for non-linear optical applications. Furthermore, the electrophilic and nucleophilic regions of the molecule were studied by molecular electrostatic potential and Fukui functions. 1H and 13C NMR chemical shifts were evaluated using GIAO method employing the same level of theory. NPA analysis and thermodynamic parameters were also calculated. Determined the structure for monomer in cis form and dimer; and intra- and inter-molecular hydrogen bonding. NLO behavior was demonstrated from HOMO-LUMO band gap energy and first order hyperpolarizability. The reactivity sites for electrophilic, nucleophilic and radical attack were found from Fukui functions. MEP and NPA analysis were carried out. NMR chemical shifts, thermodynamic parameters and rotational constants were evaluated. [ABSTRACT FROM AUTHOR]

Pyridine-3-carboxylic (or nicotinic) (P3CA) acid has been recorded by using different spectroscopic tools like NMR (13C, 1H), UV–Vis, FT-IR and FT-Raman spectral analysis. The structural conformation examined by potential energy scan for the titled compound was obtained by using DFT computations through B3LYP method with 6–311++G(d,p) basis set. Using optimized monomer structure, the dimeric structures (head-to-tail and tail-to-tail) are obtained. The title compound exhibits inter-molecular as well as intra-molecular hydrogen bonding forming a supramolecular network. The geometrical parameters of both monomer and dimer are coinciding with the observed ones. Using vibrational frequencies, Infrared and Raman intensities were computed. The rms error between the experimental and scaled quantum mechanical frequencies is 9.77 cm−1 for P3CA. From the scaled quantum mechanical method, reliable vibrational assignments were made using PED. The site of chemical reactivity and selectivity of the title compound were estimated from frontier molecular orbitals and local reactivity descriptors. The reactive areas around the compound were evaluated by using MESP. The interactions of donor and acceptor are studied by NBO analysis. The 13C and 1H NMR chemical shifts of the title compound were determined using the gauge independent atomic orbital (GIAO) method in DMSO-d6 solution. By using UV–visible spectrum, the maximum absorption wavelength was obtained and compared with the TD-DFT method. [ABSTRACT FROM AUTHOR]