气相中的 uracil 和 thymine 反应性: S(N) 2 反应及其对离开组中的电子移位的影响
Anna Zhachkina1, Jeehiun K Lee
1Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
Journal of the American Chemical Society
|November 26, 2009
概括
计算和实验研究显示,化物是比N1-deprotonated 3-methyluracil更好的离子组,这是由于电子在阳离子中的移位. 这影响了对DNA基切割修复机制的理解.
科学领域:
- 有机化学 有机化学
- 计算化学计算化学
- 生物化学 生物化学
背景情况:
- 了解离开组的能力在核友替代反应中至关重要.
- 异环离子的电子特性会影响它们的反应性.
- 酶性DNA修复机制通常涉及修改后核基的分裂.
研究的目的:
- 通过计算和实验来比较化物和N1-deprotonated 3-methyluracil的离开组能力.
- 调查电子因素,特别是电子移位,影响3 - 甲基乌拉离子的离开组能力.
- 为了评估N1-deprotonated3-methyluracil和3-methylthymine离子在酶上下文中的相对离开组的能力.
主要方法:
- 使用计算方法 (例如,DFT) 和实验技术研究了气相替代反应.
- 在N1-deprotonated3-methyluracil阳离子内分析电子脱局.
- 在模型系统和相关的酶反应中比较离开组的能力.
主要成果:
- 尽管酸度相似,但化物表现出比N1-deprotonated 3-methyluracil略有更好的离开组能力.
- 在N1-deprotonated3-methyluracil离子中的电子移位显著影响其离开组容量.
- 与N1-deprotonated-3-methylthymine anion相比,N1-deprotonated-3-methyluracil离子是一个较差的离开组.
结论:
- 离开组的能力不仅取决于酸度,还取决于电子移位.
- 乌拉和胺衍生物的分离组能力对DNA修复酶的特异性有影响.
- 计算和实验方法为化学反应和生物过程提供了互补的见解.
相关概念视频
01:30Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)
Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between the...
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between the...
02:14Leaving Groups
The nature of leaving groups strongly influences the outcome of a nucleophilic substitution reaction.
In general, in a nucleophilic substitution reaction, a nucleophile displaces a functional group, called the leaving group, from the substrate to give a substituted product. A leaving group departs the substrate molecule through heterolytic cleavage, taking the pair of electrons with it to become a relatively stable weak base in the form of an anion or a neutral molecule.
In a nucleophilic...
In general, in a nucleophilic substitution reaction, a nucleophile displaces a functional group, called the leaving group, from the substrate to give a substituted product. A leaving group departs the substrate molecule through heterolytic cleavage, taking the pair of electrons with it to become a relatively stable weak base in the form of an anion or a neutral molecule.
In a nucleophilic...
02:26SN2 Reaction: Transition State
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
01:02Radical Reactivity: Electrophilic Radicals
Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a low‐energy SOMO, which interacts...
02:45E2 Reaction: Kinetics and Mechanism
SN2 substitutions and E2 eliminations of alkyl halides proceed via a concerted pathway. While the nucleophile attacks the alpha carbon in SN2 reactions, it functions as a strong base and abstracts a beta hydrogen in the E2 mechanism. The rate-limiting transition state in E2 elimination reactions is characterized by partially broken carbon–hydrogen and carbon–halogen bonds and a partially formed pi bond between the alpha and beta carbons. The beta hydrogen and halide are eliminated...
02:26Preparation and Reactions of Sulfides
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.