Molecular structure, conformational stability, energetic and intramolecular hydrogen bonding in ground, and electronic excited state of 3-mercapto propeneselenal

In the present work, a conformational analysis of 3-mercapto propeneselenal is performed using several computational methods, including DFT (B3LYP), MP2, and G2MP2. At the DFT and G2MP2 levels the most stable conformers of title compound are characterized by an extended backbone structure, minimizing the steric repulsions between the sulfur and selenium lone pairs. Two conformers exhibit hydrogen bonding. This feature, although not being the dominant factor in energetic terms, appears to be of foremost importance to define the geometry of the molecule. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen bonding was considered using the PCM, SCI–PCM, and IEF–PCM methods. The results of analysis by quantum theory of “Atoms in Molecules” and natural bond orbital method fairly support the DFT results. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule. Further verification of the obtained transition state structures was implemented via intrinsic reaction coordinate analysis. Calculations of the 1H NMR chemical shift at GIAO/B3LYP/6–311++G** levels of theory are also presented. The excited-state properties of intramolecular hydrogen bonding in hydrogen-bonded systems have been investigated theoretically using the time-dependent density functional theory method.