RELATIVE HOMOLYTIC STRENGTHS OF N-H BONDS IN CYCLIC AND ACYCLIC DIACYLHYDRAZIDES, IMIDES AND HYDRAZOIC ACID
RELATIVE HOMOLYTIC STRENGTHS OF N-H BONDS IN CYCLIC AND ACYCLIC DIACYLHYDRAZIDES, IMIDES AND HYDRAZOIC ACID
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DOI：
10.1002/poc.610050102
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发表时间：
1992-01-01
影响因子：
1.8
通讯作者：
VAUGHN, A
中科院分区：
文献类型：
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作者：
BAUSCH, MJ;DAVID, B;VAUGHN, A
借助于由酸度和新的氧化还原数据组成的热化学循环，测定了二乙酰胺(0)、缩二脲(+1)、3，3-二甲基戊二亚胺(-3)、二乙酰肼(-16)、4，4-二甲基吡唑烷-3，5-二酮(-25)、4-二甲基吡唑烷-3，5-二酮(-25)、4-二甲基尿唑(-29)、3，3-二甲基戊二酰亚胺(-3)、4，4-二甲基吡唑烷-3，5-二酮(-25)(其中1的N-HBDE定义为0kcal-1)相对于乙酰胺(1)的N-H键离解能(Delta-BDE值)。丁二酰亚胺(-15)和1，2-二甲基尿唑(-13)(均以千卡摩尔-1为单位)。这些Delta-BDE数据提供了(A)相邻羰基最小的N-H键减弱效应的额外证据，(B)在环肼和非环肼中相邻NHC(O)R基团具有相对较大的N-H键减弱效应的证据，以及(C)相对于其氢化的前体，urazolyl自由基比吡唑烷二酮自由基更稳定的证据。在一个热化学循环中插入适当的酸度和氧化还原数据，其中包括一个允许将DMSO溶液BDEs与气相BDEs进行比较的常数，得到丁二酰亚胺和H-N3中N-H键的均解强度的估计值为93kcal mol-1。用这种方法测定的H-N3的DMSO N-H BDE与其气相值的测定结果非常一致，而丁二酰亚胺的DMSO N-H BDE则介于三种已发表的对其气相值的估计之间。
With the aid of a thermochemical cycle consisting of acidity and new redox data in dimethyl sulfoxide (DMSO) solution, homolytic N-H bond dissociation energies (DELTA-BDE values) relative to acetamide (1) (where the N-H 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 DELTA-BDE data provide (a) additional evidence for the minimal N-H bond weakening effects of adjacent carbonyl groups, (b) evidence for relatively large N-H 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 N-H bonds present in succinimide and H-N3. The DMSO N-H BDE determined in this way for H-N3 is in remarkable agreement with a determination of its gas-phase value, whereas the DMSO N-H BDE for succinimide places it intermediate between three published estimates of its gas-phase value.