Substituent effect on NH bond dissociation enthalpies of amines and amides: A theoretical study

Abstract

NOH bond dissociation enthalpies for the substituted ammonia, amine, amides, and their thio-and seleno-analogs have been studied employing ab initio and density functional methods. The orbital interactions involving lone pair of electrons on nitrogen and substituent, electrostatic interactions, spin delocalization, and hydrogen bonding are the important factors affecting the stability of the molecule and the radical. The molecule stabilization effect and radical stabilization effect have been calculated using isodesmic reactions in order to analyze the effect of substituent on the stabilization of the molecule and the radical.

Importance of asparagine on the conformational stability and chemical reactivity of selected anti-inflammatory peptides

“…In addition, proton affinity energies ðDE PA Þ provide a good method for analyzing the basicity of the amino group of the cysteine amino acid, in which a larger value is indicative of a more basic molecule. Therefore, ðDE PA Þ were calculated utilizing the isodesmic type of reactions, from which good results may be obtained in a relatively inexpensive manner [6,41]. DE PA are given by the following reaction:…”

Iron Complexes of a Proton-Responsive SCS Pincer Ligand with a Sensitive Electronic Structure

“…Spectroscopy and density functional theory (DFT) calculations using B3LYP/ZORA-def2-TZVP were further em-ployed to reveal the electronic structure of 4. The EPR spectrum of 4 in 2-methyltetrahydrofuran (MeTHF) at 77 K was modeled as an S = 1/2 spin system with g = [2.200, 2.120, 1.998] and coupling to three 31 P nuclei: two with |A| = [71,83,71] MHz and one with |A| = [0, 37, 37] MHz (Figure 4). A Mulliken spin population analysis showed spin populations of −0.036 on the axial phosphorus atoms and −0.019 on the equatorial phosphorus, in agreement with the fit to two equivalent 31 P nuclei having larger A than a third 31 P nucleus.…”

“…The N–H BDFE of 2 (56 kcal/mol) is substantially lower than the computed bond dissociation energies (BDEs) for free thioamides (90–100 kcal/mol), and its p K a of ∼21 indicates that the N–H proton is much less acidic than free thioamides, which lie in the range of 11–15 (Figure ). − It is seen from the Bordwell equation that the high p K a of 2 raises the BDFE relative to organic thioamides, but the very negative reduction potential ( E 1/2 = −1.42 V vs Fc + /Fc) of the iron­(II) center lowers the BDFE to a much larger extent. This potential is 1.0 V more negative than E 1/2 for the Fe 3+/2+ couple in a four-coordinate SNS pincer complex with an NHC as the fourth ligand, and it is 1.4 V more negative than the analogous five-coordinate SNS scaffold with two THF molecules .…”

“…In addition, we experimentally sought to "remove" the potassium completely by reacting starting material 5-Et2O with N(TMS)2 in the presence of excess (two equiv) of for free thioamides (90-100 kcal/mol), and its pKa of ~21 indicates that the N−H proton is many orders of magnitude less acidic than free thioamides, which lie in the range 11-15 (Figure 14). [72][73][74] It is seen from the Bordwell equation that the high pKa of 2 raises the BDFE relative to organic thioamides, but the very negative reduction potential (E1/2 = -1.42 V vs. Fc + /Fc) of the iron(II) center lowers the BDFE to a much larger extent. This potential is 1.0 V more negative than E1/2…”

Substituent effects on the antioxidant capacity of monosubstituted diphenylamines: a DFT study

“…[22] Later on, Poliak et al extensively studied the effects of substituent and substituted position on the N-H BDE values in diphenylamine derivatives using (U)B3LYP/6-311++G(d,p) approach. [23] Presently, several experimental methods [16,[24][25][26][27] and high level computational chemistry approaches [23,[28][29][30][31][32][33][34][35] have been used to determine the BDE(N-H). However, there remains a disadvantage because the computations for molecules with over eight heavy atoms spends a lot of time and requires ultrafast processing speed of computer.…”