The effects of substitutions on structure, electron density, resonance and intramolecular hydrogen bonding strength in 3-mercapto-propenethial

We are presenting a density functional calculation utilizing Beck three parameters hybrid, correlation functional of Lee, Yang and Parr (B3LYP), MP2 and G2MP2 levels of theory to probe the influence of R1, R2 and R3 substitutions on 3-mercapto-propenethial, estimating (i) The π-electron delocalization parameter (Q) as a geometrical indicator of a local aromaticity, (ii) the geometry-based HOMA index and (iii) intramolecular hydrogen-bond strength. The effects of F, H, Cl, CH₃, OH, and NH₂ as substituents are examined. Furthermore the topological properties of the electron density distributions for S–H⋯intramolecular bridges are analyzed in terms of the Bader theory of atoms in molecules (AIM). The electron density (ρ) and Laplacian (∇²ρ) properties, estimated by AIM calculations, indicate that S⋯H bond possesses low ρ and positive ∇²ρ values which are in agreement with electrostatic character of the HBs, whereas S–H bonds have covalent character (∇²ρ < 0). Natural population analysis data, the electron density and Laplacian properties, as well as, υ_(S–H) and γ_(S–H) have been used to evaluate the hydrogen bonding interactions.