Conformations, structure, vibrations, chemical shift and reactivity properties of isoquinoline–1–carboxylic acid and isoquinoline–3–carboxylic acid – Comparative investigations by experimental and theoretical techniques

Abstract

The most stable conformer of isoquinoline–1–carboxylic acid (IQ1CA) and isoquinoline–3–carboxylic acid (IQ3CA) are determined and the geometry has been optimised with B3LYP method using high level 6–311++G** and cc–pVTZ basis sets. The structure, electronic properties, vibrational fundamental modes, thermodynamic properties and chemical shifts of the compounds are investigated. The vibrational fundamental modes are assigned and analysed by utilising FT–IR and FT–Raman spectrum of the compounds recorded in the range of 4000–400 and 4000–100 cm−1, respectively. The LUMO–HOMO energy difference is determined to explain the charge transfer within the molecule. The molecular electrostatic potential and total electron density of the molecules are determined to explain the size, shape and the reactive sites (polar) of the molecules. The 1H and 13C NMR chemical shifts of the compounds are determined by Gauge Invariant Atomic Orbital (GIAO) method using DMSO–d6 solvent by B3LYP/cc–pVTZ method. The local and global chemical reactivity properties of the compounds have been investigated with the help of global and local reactivity descriptors.