Stereoelectronic Effects Related to the Anomeric Effect on the Conformation Behavior of Methanedithiol Using Density Fitness Theory and NBO Analysis of Spatial Isomers

  • Elahe Jalali


This study has examined the effects of Generalized Anomeric Effects (GAE) resulting from electron transfer, the mutual electrostatic and spatial impacts on conformation behavior of methanedithiol. B3LYP/Def 2-TZVPP method and NBO analysis have been applied to study the Generalized Anomeric Effects (GAE) resulting from transfer of electron, electrostatic and spatial impacts and formulate behavior of methanedithiol. According to the results of B3LYP/Def 2-TZVPP, gauche-gauche (g.g) conformation was076 and 12.26 more stable than quasi-anti.gauche (qa.g) and gauche.gauche* (g.g*) conformations respectively. According to NBO analysis results, the GAE for gg. Qa.g and g.g* was 44.18, 7.29, and 16.68 Kcal/mol respectively. According to the results, GAE would follow an ascending order from g.g. to qa.g confirmation; however, it follows a descending trend from qa.g to g.g* conformation. Thus, the variation trend of GAE is not the same as the trend of energy variation between different conformations of g.g, qa.g and g.g* of methanedithiol. Thus, the GAE doesn’t justify the energy variation of different conformations of methanedithiol.

The electrostatic model has been studied to investigate the conformation properties of methanedithiol. The results suggest that the dipole moment of g.g., qa.g, and g.g* of methanedithiol was 0.4865, 1.8172, and 1.4829 Debye respectively. According to the results, the dipole moments will increase from g,g, and g,g* conformations. According to the trend of variations, the dipole moment of methanedithiol is the same as the trend of energy variation between g,g,,qa., g, and g.g* conformations of methanedithiol.

Besides, the results of NBO analysis suggest that Total Steric Exchange Energy (TSEE) for g.g,, qa.g, and g.g* conformations of methanedithiol are 92.74, 63.88, and 62.68 Kcal/mol respectively. Thus, the TSEE variation trend in g.g., qa.g and g.g* conformations of methanedithiol is not the same as the trend of energy variation among them. Therefore, it can be suggested that among GAE energy, electrostatic model, and TSE, the electrostatic model is a good descriptor of methanedithiol's conformation behavior. Structural parameters of different conformations of methanedithol are affected by electron transfer. The studies on structural parameters suggest that the length of C-S bonds in g.g and g.g* is equal; however, one f the C-S bonds in qa.g conformation is shorter than another. As evident from the following figure, for studying the potential energy level for different conformations of methanedithiol, we'd model its g.g conformation. Upon varying the length of C3-S2 bond and placing an energy dam of 2.83 Kcal/mol. We'll arrive in qa.g conformation which is 1.57 Kcal/mol more stable than g.g. conformation. Sustained rotation around C3-S2 bond, and surpassing the energy dam of 0.43, we'd arrive in g,g* conformation which is 0.98 Kcal/mol less stable than g.g conformation. To transform g.g* conformation to g.g, about 2.62 Kcal/mol of energy is required to surpass the symmetrical eclipsed conformation of C2V to g.g.