A theoretical study on NH bond dissociation enthalpies of oxo, thio and seleno carbamates and their N-protonated and N-deprotonated species

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• 作者：D. Kaur ; Rupinder Preet Kaur
• 关键词：Bond dissociation enthalpy ; Proton affinities ; Deprotonation affinities ; Electron delocalization ; Spin delocalization
• 刊名：Journal of Molecular Structure: THEOCHEM
• 出版年：2008
• 出版时间：15 June 2008
• 年：2008
• 卷：858
• 期：1-3
• 页码：94-100
• 全文大小：244 K

文摘

The effect of N-protonation and N-deprotonation on structure, Nbond"" title=""single bond"" border=""0"">H bond dissociation enthalpies (BDEs) and stabilities of radicals formed on H-abstraction from nitrogen atom of carbamates and their thio- and seleno-analogs have been investigated. For those molecules where experimental results are available for comparison, the ROB3LYP/6-311++G(d,p)//B3LYP/6-31+G* theoretical level is in agreement within the estimated experimental uncertainty. The Nbond"" title=""single bond"" border=""0"">H BDE of carbamates H₂NC(=X)YCH₃ [X = O; Y = O, S, Se] are higher but lower when X = S, Se and Y = O, S, Se in comparison to Nbond"" title=""single bond"" border=""0"">H BDE of NH₃. DFT calculations indicate that the Nbond"" title=""single bond"" border=""0"">H bond dissociation enthalpies are decreased by protonation and deprotonation at nitrogen atom; but the effect of deprotonation is rather smaller than the protonation. The variations are analyzed in terms of stabilities of molecules, their protonated and deprotonated species along with their respective radicals. The electron delocalization from nitrogen, X and Y atoms, electrostatic interactions, conjugative interactions and spin delocalization are the important factors affecting the stability. The spin delocalization and shift of radical center to chalcogen X (X = S, Se) are the main determinants for radical stability.