DFT analysis of substituent effects on electron-donating efficacy of pyridine

Abstract

Studies on pyridine, C5H5N, and pyridine derivatives (simulations) of the type C5(X) n H5−n N (X = −C≡CH; –C≡CF; –C≡N; –CH(=O)) are carried out using the DFT method employing B3LYP/LanL2DZ level of theory. The effects of substituent modification (type and position) on electron density enrichment of pyridyl nitrogen atoms and thus its effectiveness as a donor atom for incoming metal ions have been investigated. Computational results showed that first, substituents exert interesting effects on both the accumulated charge density on nitrogen and the geometrical parameters (C2=N bond length and C2···N···C6 bond angle) of the examined pyridine simulations. Second, depending on the type of the substituent, substituents showed variable trends in effect. For example, –C≡CH and –C≡CF show a similar trend, which is overall noticed to be different from that observed for –C≡N –CH(=O). Third, the influence of substituent modification on electronic localization/delocalization is further viewed by calculating the charge density distribution surfaces and the occupancy of the frontier HOMO molecular orbitals. Gathered images of charge density surfaces and HOMO orbitals for all simulates clearly showed how charge density is distributed over the pyridine system and truly found to be very helpful in providing deep insight into how charge density is accumulated over nitrogen specifically. In result, –C≡CF among all, was found to enrich the charge density on pyridyl nitrogen the most. This was attributed to the existence of fluorine atoms in the structure of the attached substituent. Fluorine atom, was able of extending the electron density delocalization—pathway more than the other substituents do. Actually, this investigation is a pursuing to our research work which basically aims to put under control various variables that would promote the inorganic complex to be a good chromophore in low energy regions and to be further employed in chemosensation. In this report, we attempt to move one extra step ahead and expand our knowledge to wisely engineer and design a feasible chemosensor that is capable of responding in the visible region.