On the performance of molecular tailoring approach for estimation of the intramolecular hydrogen bond energies of RAHB systems: a comparative study

Abstract

In the current research, the performance of molecular tailoring approach (MTA) for estimation of the intramolecular hydrogen bond (IMHB) energies of the simple resonance-assisted hydrogen bond (RAHB) systems was theoretically investigated. First, a wide range of malonaldehyde derivatives (36 members) including the F, Cl, Br, CN, NO2, ethen (-CH=CH2), ethin (-C ≡ CH), CF3, OCH3, C2H5, CH3, and Ph substitutions at R1, R2, and R3 positions were considered. Then, all of these molecules at MP2/6-311++G(d, p) level of theory have been optimized and their MTA energies were calculated. Furthermore, various qualitative descriptors of IMHB such as structural, spectroscopic, topological, and molecular orbital parameters were considered, and all of correlations between these factors and MTA energies were explored. According to their regression coefficients (R2), the linear characteristic of correlations obeys the following order:$$ {H}_{\mathrm{H}\dots \mathrm{O}}>{d}_{\mathrm{O}-\mathrm{H}}>{E}_{\mathrm{CT}}>{V}_{\mathrm{H}\bullet \bullet \bullet \mathrm{O}}>{\rho}_{\mathrm{H}\bullet \bullet \bullet \mathrm{O}}>{\nu}_{\mathrm{O}-\mathrm{H}}>{d}_{\mathrm{H}\bullet \bullet \bullet \mathrm{O}}>{d}_{\mathrm{O}\bullet \bullet \bullet \mathrm{O}} $$$$ 0.952\kern1.5em 0.940\kern1.2em 0.936\kern0.75em 0.914\kern1.2em 0.901\kern1.2em 0.834\kern1em 0.789\kern1.3em 0.755 $$ These correlation coefficients have compared with the corresponding R2 values of other models such as RRM, RBM, GCM, IRM, and OCM, which leads to the following order of linearity:$$ \mathrm{MTA}\ge \mathrm{RRM}>\mathrm{RBM}>\mathrm{GCM}>\mathrm{IRM}>\mathrm{OCM}. $$ Finally, the significance of π-electron delocalization (π-ED) of RAHB rings is also evaluated by the geometrical factor of Gilli (λ) and the harmonic oscillator model of aromaticity (HOMA) that presents the excellent linear correlations with MTA energies, which may be implied on the validity of RAHB theory.