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A kinetic study is reported for the reactions of 2-methoxy-3-nitropyridine 1a and 2methoxy-5-nitropyridine 1b with three secondary amines 2a-c (morpholine, piperidine, and pyrrolidine) in aqueous solution at 20 • C. The Brønsted-type plots are linear with nuc = 0.52 and 0.55 for pyridines 1a and 1b, respectively, indicating that the reaction proceeds through a S N Ar mechanism in which the first step is the ratedetermining step. Additional theoretical calculations using the DFT/B3LYP method confirm that the C-2 carbon being the most electrophilic center for the both pyridines 1a and 1b. The second-order rate constants have been used to evaluate the electrophilicity parameters E of 1a and 1b according to the linear free energy relationship log k (20 • C) = s N (N + E). The E parameters thus derived are compared with the electrophilic reactivities of a large variety of anisoles. The validity of these E values has been satisfactorily verified by comparison of calculated and experimental second-order rate constants for the reactions of pyridines 1a and 1b with anion of ethyl benzylacetate. K E Y W O R D S density functional theory, electrophilicity parameter (E), equation of Mayr, kinetics, S N Ar, substituted pyridine Int J Chem Kinet. 2019;51:249-257.

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ABSTRACT:In this article, we present quantum chemical calculations, based on density functional theory (DFT), performed to investigate the geometries and the opto-electronic properties of a new synthesized graft copolymer based on poly(N-vinylcarbazole) (PVK) and poly(3-methylthiophene) (PMeT) named PVK-3MeT. First, we have theoretically computed and compared the structural, optical, and vibrational parameters of both neutral and doped states. In addition, the excited state was theoretically obtained by the ab initio RCIS/ STO-3G method. To assign the absorption and emission peaks observed experimentally, we computed the energies of the lowest singlet excited state with the time-dependent density functional theory (TD-DFT) method. Electronic parameters such as the HOMO-LUMO band gap, the ionization potential (IP), and electron affinity (EA) are extracted. Calculations show that the PVK-3MeT copolymer is nonplanar in its ground neutral state. Meanwhile, upon doping or photoexcitation, an enhancement of the planarity is observed, resulting on a decrease of the inter-ring torsion angle between 3-methylthiophene units. Such modifications in the geometric parameters induce a dramatic change on the HOMO and LUMO orbitals in the doped or excited states.