Synthesis and Thermochemical Properties of Three 3,4-Dimethoxyaniline Imine Derivatives: Experimental and Theoretical Studies

This study focuses on the thermal and energetic properties of three arylimine derivatives synthesized from 3,4-dimethoxyaniline. Melting points and fusion enthalpies were assessed through differential scanning calorimetry, while combustion energies were determined using a static bomb semimicro calorimeter. Thermogravimetric analysis was employed to evaluate sublimation enthalpies, enabling the calculation of standard molar enthalpies of formation (p° = 0.1 MPa) at T = 298.15 K for both crystalline and gaseous phases. Theoretical computations, based on density functional theory (DFT), were performed to determine gas-phase enthalpies of formation and examine the relationship between electronic structures in the H–C=N– group and NMR chemical shifts, comparing theoretical and experimental results.