A comprehensive theoretical study of mutual interactions between the intramolecular hydrogen bond and π-electron delocalization of RAHB units with the benzene rings in salicylaldehyde and ortho-aminobenzaldehyde with their thio and seleno analogues

A comprehensive theoretical study of mutual interactions between the resonance-assisted hydrogen bond (RAHB) units and benzene rings in salicylaldehyde and ortho-aminobenzaldehyde with their thio and seleno analogues, at the M062X/6-11++G(d,p) level of theory, was carried out. First, we evaluated the intramolecular hydrogen bond (IMHB) strength of the mentioned compounds by various descriptors, such as geometrical, spectroscopic, topological, molecular orbital, and energetic parameters, and then compared with the corresponding results of malonaldehyde and beta-aminoacrolein with their thio and seleno analogues. According to the theoretical results, it was found that the merging of benzene rings and RAHB units reduced the strength of the IMHB in all of the benchmark systems. The magnitude of these reductions in the O-H center dot center dot center dot Y systems is greater than that of the N-H center dot center dot center dot Y ones. Also, the substitution of S and Se atoms instead of O increased the IMHB strength and obeyed the following order; X-H center dot center dot center dot S > X-H center dot center dot center dot S > X-H center dot center dot center dot O. Second, a set of aromaticity indices such as the harmonic oscillator model of aromaticity (HOMA), the nucleus-independent chemical shift (NICS), the para delocalization index (PDI), and the average two-center index (ATI) were applied to evaluate the significance of the aromaticity of benzene rings and pi-ED of RAHB units in the studied molecules. The comparison between these results and the respective amounts of the benzene ring, malonaldehyde, and beta-aminoacrolein analogues reveals that the coupling of benzene and RAHB rings decreased the pi-ED and aromaticity in both of them. These reductions approximately increase with the replacement of O by N in the proton donor group. Finally, the results show that the pi-ED of RAHB units increases with substitution of O by S and Se, while for the aromaticity of the benzene rings the reverse process is observed. The majority increment in the pi-ED of RAHB units and also a reduction in the aromaticity of the benzene rings are related to an X-H center dot center dot center dot Se system that is followed by X-H center dot center dot center dot S and X-H center dot center dot center dot O systems.