Calculation of intramolecular hydrogen bonding strength and natural bond orbital (NBO) analysis of naphthazarin with chlorine substitution

The hydrogen bond strength, geometry optimization and 1H NMR for naphthazarin (NZ) and its chlorine substitutions have been calculated at the B3LYP/6-31G** theoretical level. lculated chemical shifts of the chelated proton for all molecules, using GIAO method, are well correlate with the calculated geometrical parameters results. ing to the calculated results, substitutions near the hydroxyl groups and near the carbonyl groups increases and decreases the strength of the hydrogen bond, respectively. ural bond orbital (NBO) method, the effect of substitution on the hydrogen bond strength, the charge distributions, steric effects, and electron delocalization in the studied compounds were investigated. The natural bond orbital analysis very well explains the calculated results of substitution of chlorine atoms on the hydrogen bond strength.