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Determination of the Gas-phase Acidities of Oligopeptides
Published on: June 24, 2013
替代酸的螺旋自组装:较弱的X...X和C-H...X相互作用的影响
J Narasimha Moorthy1, R Natarajan, Prasenjit Mal
1Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India.
Journal of the American Chemical Society
|June 6, 2002
概括
通过利用键和较弱的相互作用,性阻碍的碳酸盐通过利用键和较弱的相互作用形成螺旋晶体结构. 这与其他形成带状排列的替代酸形成鲜明对比,显示了微妙的相互作用如何影响晶体包装.
科学领域:
- 晶体学 晶体学是指结晶学.
- 超分子化学 超分子化学
- 有机化学 有机化学
背景情况:
- 晶体包装是由分子间力量控制的.
- 键通常主导着碳基组相互作用.
- 较弱的相互作用 (例如,素结合) 可以影响晶体结构.
研究的目的:
- 为了研究结晶包装的硬质加重的素替代二氧化碳酸.
- 阐明结和较弱相互作用在决定晶体结构中的作用.
- 为了比较不同替代碳素酸系统中的包装图案.
主要方法:
- 用X射线结晶学进行详细的结构分析.
- 对分子间相互作用的分析 (O-H...O,X...X,C-H...X).
- 对相关化合物的晶体结构进行比较.
主要成果:
- 通过O-H...O键和较弱的相互作用观察到在素替代的二碳酸 (1-4) 中的新型螺旋晶体包装.
- 密集包装利用了强键和较弱的X...X和C-H...X相互作用.
- 和替代的杜伦碳酸 (6,7) 显示带/丝带图案,涉及二聚体形成和X...X相互作用.
结论:
- 较弱的分子间相互作用显著影响并可以修改强大的晶体图案,如碳酸盐中心对称二分体.
- 观察到的螺旋和带/丝带结构突出显示了替代碳酸酸中的晶体工程的多功能性.
- 了解这些包装原理对于设计具有特定固态特性的材料至关重要.
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In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Molecular Structure and Acidity
An acid can be deprotonated to form a conjugate base or an anion. If the produced anion is more stable, then the acid is stronger. On the contrary, if the anion is unstable, then the acid is weaker. Hence, to determine the acidity of the compound, the stability of its conjugate base is studied using various factors.
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...
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Structures of Carboxylic Acid Derivatives
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Acidity and Basicity of Carboxylic Acid Derivatives
Carboxylic acids are the strongest among organic acids, as they readily lose the hydroxyl proton to form a resonance-stabilized carboxylate ion. In comparison, the acid derivatives lack acidic hydrogens directly attached to a functional group. In these compounds, the acidic nature arises from their ability to lose α hydrogens, making them weakly acidic.
The relative acidic strength of the derivatives can be explained based on the extent of resonance stabilization of the conjugate base. The...
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Relative Reactivity of Carboxylic Acid Derivatives
Carboxylic acid derivatives such as acid halides, anhydrides, esters, and amides undergo nucleophilic acyl substitution reactions with varying degrees of reactivity.
A key factor in assessing the reactivity of the acid derivatives is the basicity of the substituent or the leaving group. The lower the basicity of the leaving group, the higher the reactivity of the derivative. The basicity of the leaving group follows this order:
Halide ions < Acyloxy ions < Alkoxy ions < Amine ions
A key factor in assessing the reactivity of the acid derivatives is the basicity of the substituent or the leaving group. The lower the basicity of the leaving group, the higher the reactivity of the derivative. The basicity of the leaving group follows this order:
Halide ions < Acyloxy ions < Alkoxy ions < Amine ions
Substituent Effects on Acidity of Carboxylic Acids
The acidity of carboxylic acids is influenced by the nature of the substituents bounded to the functional group. The acid strength is determined by the stability of the carboxylate anion—the conjugate base formed by dissociating the corresponding carboxylic acid.

