实验和理论研究的热分解的异环酸化物
1Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA.
Journal of the American Chemical Society
|August 2, 2001
概括
替代的2 - 尼托西米诺 - 索提亚林通过单分子途径经历热分解. 计算分析揭示了一种涉及循环和气 (N2) 损失的逐步机制,计算的障碍与实验数据相匹配.
科学领域:
- 有机化学 有机化学
- 物理化学 物理化学
- 计算化学计算化学
背景情况:
- 合成替代的2 - - 尼托西米诺 - - 索提亚zolines (2) 通过化2 - - 尼托西米诺 - - 索提亚zolines (6).
- 开始研究这些新型化合物的热分解动力学和机制.
研究的目的:
- 为了阐明一系列替代的2-nitrosiminobenzothiazolines的热分解的动力和机械途径.
- 将实验激活参数与理论计算进行比较,以了解分解过程.
主要方法:
- 用第一阶动力学研究各种溶剂 (甲醇,乙二,1,4-二,环) 中的热分解的动力学研究.
- 最初的分子轨道理论 (MP2/6-31G*) 和更高层次的计算 (MP4 ((SDQ,FC)/6-31G*) 来确定基态结构和过渡状态.
- 激活参数 (Delta H(++),Delta S(++)) 和键解离能量的计算.
主要成果:
- 热分解跟随第一阶动力学,表明单分子分解机制.
- 确定了实验激活参数 (例如,Delta H(++) = 25.3 +/- 0.5 kcal/mol 在环素中).
- 计算的气相屏障高度 (25.2 kcal/mol) 对于模型化合物中的N2损失,与实验值密切匹配.
- 发现了一个不寻常的潜在能量表面,在旋转和环闭过渡状态之间存在直接联系.
结论:
- 分解是通过一个分阶段的机制进行的,涉及化胺循环,然后是 (N2) 挤出.
- 计算结果支持拟议的机制,并准确预测实验激活障碍.
- 该研究强调了旋转和键形成过渡状态的独特脱,与协调的环周反应形成鲜明对比.
相关概念视频
01:01Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
01:12Acid Halides to Esters: Alcoholysis
Alcoholysis is a nucleophilic acyl substitution reaction in which an alcohol functions as a nucleophile. Acid halides react with alcohol to produce esters. The mechanism proceeds in three steps:
01:13Esters to Carboxylic Acids: Acid-Catalyzed Hydrolysis
Hydrolysis of esters under acidic conditions proceeds through a nucleophilic acyl substitution. In the presence of excess water, the reaction proceeds in a reversible manner, forming carboxylic acids and alcohols.
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
00:54Radical Formation: Homolysis
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
00:51Radical Formation: Elimination
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect to...
01:41Reactions of Carboxylic Acids: Introduction
Carboxylic acids possess an acidic –COOH functional group. The acidity can be attributed to the resonance stabilization of their conjugate base, wherein the negative charge is delocalized over both oxygen atoms.