Authors: Vadim V Nazarenko
Comments: 99 Pages.
DENSITY FUNCTIONAL THEORY (DFT) INVESTIGATION OF RSNNSR SYSTEMS
The structural variations and stabilities of RSNNSR systems were studied using the hybrid density functional theory (B3LYP) at various basis set levels. Computational methodology was based on the locally dense basis set approach (LDBS) that assigns various levels of the basis sets accordingly to the previously calibrated results that could be correlated to the experimental data.
The present study investigated the effect of the substituents (R) on the structure and the stabilities of RSNNSR systems. There were totally ten systems studied where R: H, CH3, CF3, tert-Butyl, C6H6, p-NO2C6H6 , p-CH3OC6H6.
The calculations revealed that the stability of the S-N bond is enhanced if there is a combination of the electron-releasing effect and the electron-withdrawing one that creates a push-pull effect (captodative effect) in the system. An increase of a positive charge on one of the sulfur atoms and a negative charge on the adjacent nitrogen atom increases delocalization of one the S’s lone pairs that creates a conjugation with the neighboring N atom and the β carbons through 2pπ-3pπ interactions.
The push-pull effect also influenced structural characteristics of the systems. One of the most notable ones is the variation of the NSCC dihedral angle in some of our systems from 89° to 21°
Standard enthalpies of formation are used for assessing the efficiency and safety of
chemical processes in the chemical industry. However, the number of compounds for
which the enthalpies of formation are available is many orders of magnitude smaller
than the number of known compounds. Thermochemical data prediction methods are
therefore clearly needed. Several commercial and free chemical databases are
currently available, the NIST WebBook being the most used free source.
To overcome this problem a cheminformatics system was designed and built with two
main objectives in mind: collecting and retrieving critically evaluated thermochemical
values, and estimating new data. In its present version, by using cheminformatics
techniques, ThermInfo allows the retrieval of the value of a thermochemical property,
such as a gas-phase standard enthalpy of formation, by inputting, for example, the
molecular structure or the name of a compound. The same inputs can also be used to
estimate data (presently restricted to non-polycyclic hydrocarbons) by using the
Extended Laidler Bond Additivity (ELBA) method. The information system is
publicly available at http://www.therminfo.com or http://therminfo.lasige.di.fc.ul.pt.
ThermInfo’s strength lies in the data quality, availability (free access), search
capabilities, and, in particular, prediction ability, based on a user-friendly interface that
accepts inputs in several formats.