Crystal Structure, Hirshfeld Surface Analysis, DFT Calculations, HOMO–LUMO Study, and UV–Visible Spectrum of 2,4,5-Trimethoxybenzaldehyde

Abstract The crystal structure of the title compound, 2,4,5-trimethoxybenzaldehyde (C₁₀H₁₂O₄), was determined at ambient temperature (293 K) using single-crystal X-ray diffraction (XRD). The structure was solved via direct methods and refined over 173 parameters. The compound crystallizes in the monoclinic crystal system, adopting the space group P 1 21/n, with four molecules per unit cell (Z = 4). The refined unit cell parameters at 293 K are: a = 4.0759(8) Å, b = 7.454(2) Å, and c = 31.817(5) Å. The molecular framework is nearly planar, with a root mean square (r.m.s.) deviation of 0.027 Å for the non-hydrogen atoms and a maximum deviation of 0.081 Å observed for atom C8. Within the crystal lattice, molecules interact through C—H···O hydrogen bonds, forming zigzag chains oriented along the a-axis. Hirshfeld surface analysis indicates that H···H interactions dominate the intermolecular contacts, contributing 44.2% to the overall surface. The optimized geometry bond lengths, bond angles of the molecule were calculated by using DFT method with functional B3LYP and 6-311G(d) basis set and assuming C₁ symmetry. Electrostatic potential mapping of the molecule, computed within a range of −0.05 to +0.05 atomic units (a.u.), highlights regions of varying electron density. The UV–visible absorption spectrum exhibits two major peaks centered at 335 nm and 345 nm, corresponding to electronic transitions. Additionally, frontier molecular orbital analysis reveals that the energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are −0.214 a.u. and −0.056 a.u., respectively.