短的分子内键:malonaldehyde的衍生物与对称的替代剂
Jacqueline C Hargis1, Francesco A Evangelista, Justin B Ingels
1Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602-2525, USA. jhargis@uga.edu
Journal of the American Chemical Society
|December 4, 2008
概括
这项研究探讨了具有非常短键的甲衍生物. 研究人员发现化合物具有极低的能量障碍,用于分子内原子的转移,使障碍高度的估计更大的系统.
科学领域:
- 计算化学计算化学
- 量子化学 是一个量子化学.
- 分子建模分子建模
背景情况:
- 马隆甲衍生物正在研究它们在形成非常短的键中的潜力.
- 分子内键在化学反应性和分子性质中至关重要.
- 了解键动态是设计新型化学系统的关键.
研究的目的:
- 系统地研究带有电子吸收组和电子捐赠/硬质阻碍替代物的malonaldehyde衍生物.
- 探索非常短的分子内键 (r(OO) <2.450 Å) 的形成.
- 计算和分析分子内原子转移的能量障碍.
主要方法:
- 利用相关的电子结构方法,包括二阶扰动理论和合集群理论.
- 采用了相关性一致性基础集的宁等级 (cc-pVXZ,X=D,T,Q,5).
- 应用焦点分析,将能量障碍推断到完整基准集 (CBS) 极限,包括核心相关性和零点振动能量校正.
主要成果:
- 鉴定出了7种具有极短分子内键的分子.
- 计算了分子内原子转移的经典障碍,其中甲显示了大约4kcalmol-1的障碍.
- 发现了两种化合物,二甲胺 (0.43 kcal mol ((-1)) 和二甲胺 (0.60 kcal mol ((-1))),具有非常低的障碍.
结论:
- 建立了B3LYP和合集群 (CBS极限) 能量障碍之间的经验关系.
- 开发了一种方法,以计算方式估计大型分子系统的屏障高度.
- 这些发现提供了对具有可调节键和反应性的分子设计的见解.
相关概念视频
01:14Alkylation of β-Diester Enolates: Malonic Ester Synthesis
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
01:35Loss of Carboxy Group as CO2: Decarboxylation of Malonic Acid Derivatives
Just like β-keto acids—which upon thermal decarboxylation form ketones—β-dicarboxylic acids undergo decarboxylation to generate monocarboxylic acids with the liberation of carbon dioxide.
01:04Structures of Aldehydes and Ketones
Vanillin—a flavoring agent in vanilla, cinnamaldehyde—a molecule responsible for the distinct smell of cinnamon, and acetone—a strong-smelling ingredient in nail polish removers, all belong to a class of carbonyl compounds called aldehydes and ketones (Figure 1). Although both aldehydes and ketones contain the characteristic carbonyl (C=O) bond, their chemical structures vary with respect to the groups directly attached to the carbonyl carbon.
In aldehydes (Figures 1a and 1b), the carbonyl...
In aldehydes (Figures 1a and 1b), the carbonyl...
01:20Aldehydes and Ketones with Water: Hydrate Formation
An oxygen-based nucleophile, like water, can undergo addition reactions with aldehydes and ketones. The reaction leads to the formation of hydrates, also referred to as 1,1-diols or geminal diols.
The formation of hydrates is a reversible reaction. Hydrate formation is influenced by steric and electronic factors accompanying the alkyl substituents on the carbonyl group: The rate of hydrate formation increases with a decrease in the number of alkyl groups attached to the carbonyl carbon. Hence,...
The formation of hydrates is a reversible reaction. Hydrate formation is influenced by steric and electronic factors accompanying the alkyl substituents on the carbonyl group: The rate of hydrate formation increases with a decrease in the number of alkyl groups attached to the carbonyl carbon. Hence,...
01:32Aldehydes and Ketones with HCN: Cyanohydrin Formation Overview
Cyanohydrins are compounds that contain –CN and –OH groups on the same carbon atom. They are formed by the nucleophilic addition of the cyanide ions to the carbonyl group. Cyanide ions are highly basic and nucleophilic and can be generated from HCN under aqueous conditions. However, since HCN is a weak acid, the number of cyanide ions generated is very small. Hence, a small amount of base or KCN/NaCN is added to HCN to increase the concentration of the cyanide ions in the reaction mixture.
01:19Aldehydes and Ketones with Alcohols: Hemiacetal Formation
Similar to water, alcohols can add to the carbonyl carbon of the aldehydes and ketones. The addition of one molecule of alcohol to the carbonyl compound forms the hemiacetal or half acetal. As depicted below, in a hemiacetal, the carbon is directly linked to an OH and OR group.