Relative homolytic strengths of N?H bonds in cyclic and acyclic diacylhydrazides, imides and hydrazoic acid

Autor: L. H. Wang, Mark J. Bausch, A. Vaughn, V. Prasad, B. David
Rok vydání: 1992
Předmět:
Zdroj: Journal of Physical Organic Chemistry. 5:1-6
ISSN: 1099-1395
0894-3230
DOI: 10.1002/poc.610050102
Popis: With the aid of a thermochemical cycle consisting of acidity and new redox data in dimethyl sulfoxide (DMSO) solution, homolytic NH bond dissociation energies (ΔBDE values) relative to acetamide (1) (where the NH BDE for 1 is defined as 0 kcal mol−1) were determined for diacetamide (0), biuret (+ 1), 3,3-dimethylglutarimide (−3), diacetylhydrazine (−16), 4,4-dimethylpyrazolidine-3,5-dione (− 25), 4-dimethylurazole (−29), hydrazoic acid (−15), succinimide (−15) and 1,2-dimethylurazole (−13) (all values in kcal mol−1). These ΔBDE data provide (a) additional evidence for the minimal NH bond weakening effects of adjacent carbonyl groups, (b) evidence for relatively large NH bond weakening effects of adjacent —NHC(O)R moieties in both cyclic and acyclic hydrazides and (c) evidence suggesting that urazolyl radicals are more stable than pyrazolidinedionyl radicals, relative to their hydrogenated precursors. Inserting the appropriate acidity and redox data for hydrazoic acid into a thermochemical cycle that includes a constant that permits comparison of DMSO solution BDEs with gas-phase BDEs yields estimates of 93 kcal mol−1 for the homolytic strengths of the NH bonds present in succinimide and HN3. The DMSO NH BDE determined in this way for H—N3 is in remarkable agreement with a determination of its gas-phase value, whereas the DMSO NH BDE for succinimide places it intermediate between three published estimates of its gas-phase value.
Databáze: OpenAIRE
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