A computational investigation on the molecular structure, electronic properties and intramolecular hydrogen bonding interaction of 1,1,1-trifluoro-4-mercaptobut-3-ene-2-thione in ground and electronic excited state
The hydrogen bond (HB) strength, geometry optimization, vibrational frequencies and several well-established indices of aromaticity in 1,1,1-trifluoro-4-mercaptobut-3-ene-2-thione and its 15 derivatives in two positions, R1 and R2, have been investigated by means of the density functional theory (DFT) method with 6-311++G** basis set in the gas phase. The obtained results show that the HB strength is mainly governed by resonance variations inside the chelate ring induced by the substituent groups. The following substituents have been taken into consideration: NO2, SCF3, Ph, PhOCH3, SCOCH3, CH2OCH3 and CH2OH. The strongest S–H···S HBs belong to PhOCH3-substituted system in both positions, whereas NO2 and H substitutions in R1 and R2 positions, respectively, produce the weakest S–H···S hydrogen bridges. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent DFT method. Natural bond orbital analysis is also performed for a better understanding of the nature of intramolecular interactions. The electron density and Laplacian (∇2ρ) properties, estimated by atoms in molecule calculations, indicate that the H···S bond possesses low ρ, positive ∇2 ρ and HC<0, which are in agreement with the partially covalent character of HBs.