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相关概念视频

VSEPR Theory and the Basic Shapes02:52

VSEPR Theory and the Basic Shapes

Overview of VSEPR Theory
Acid/Base Strengths and Dissociation Constants03:02

Acid/Base Strengths and Dissociation Constants

The relative strength of an acid or base is the extent to which it ionizes when dissolved in water. If the ionization reaction is essentially complete, the acid or base is termed strong; if relatively little ionization occurs, the acid or base is weak. There are many more weak acids and bases than strong ones. The most common strong acids and bases are listed below:
Relative Strengths of Conjugate Acid-Base Pairs02:29

Relative Strengths of Conjugate Acid-Base Pairs

Brønsted-Lowry acid-base chemistry is the transfer of protons; thus, logic suggests a relation between the relative strengths of conjugate acid-base pairs. The strength of an acid or base is quantified in its ionization constant, Ka or Kb, which represents the extent of the acid or base ionization reaction. For the conjugate acid-base pair HA / A−, the ionization equilibrium equations and ionization constant expressions are
Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
Extraction: Effects of pH00:53

Extraction: Effects of pH

Consider a neutral form of an amine, B, with a partition coefficient, K, in a liquid mixture containing organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes, and the charged form is usually more soluble in the aqueous phase. Suppose the conjugate acid form of the amine is soluble only in the aqueous phase while the base form is soluble in both phases. Then the distribution coefficient, D, can be given as the ratio of amine concentration in the...

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Determination of the Gas-phase Acidities of Oligopeptides
11:00

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Published on: June 24, 2013

密度函数理论研究了基胺和基胺的区域选择性基和基-基脱的机制.

Fredrik Haeffner1, Madeleine A Jacobson, Ivan Keresztes

  • 1Department of Chemistry, Brown University, Providence, RI 02912, USA. fredrick_haeffner@brown.edu

Journal of the American Chemical Society
|December 23, 2004
PubMed
概括

这项研究使用了计算方法来探索胺和胺化合物中的脱质化机制. 计算显示,对于一个化合物而言,在基位置的区域选择性去质子化,而对于另一种化合物而言,在cis-vinylic位置的动力控制.

科学领域:

  • 计算化学的计算化学
  • 有机合成 有机合成
  • 反应机制 反应机制

背景情况:

  • 在有机合成中,区域选择性去质子是非常重要的.
  • 了解这些机制有助于设计新的合成路径.
  • 胺和胺衍生物是多功能合成中间体.

研究的目的:

  • 研究控制区域选择性去质子化的机制.
  • 阐明在N--N-替代胺中控制脱位的因素.
  • 将计算预测与实验观测进行比较.

主要方法:

  • 密度函数理论 (DFT) 的计算.
  • 使用了B3LYP/6-31+G理论水平.
  • 对N--N--三-丁胺 (1) 和N--N--三甲基-胺 (2) 的反应途径进行了研究.

主要成果:

  • 计算准确地预测了化合物1的排他性脱质,与实验数据相匹配.
  • 计算分析表明,对于化合物2的独家cis-vinylic脱.
  • 动力控制被确定为化合物2中观察到的区域选择性的驱动力.

结论:

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  • DFT计算提供了对去质子化机制的可靠见解.
  • 这项研究强调了不同胺系统中不同替代物的独特反应性.
  • 这些发现有助于理解有机金属化学中的区域选择性.