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相关概念视频

Factors Affecting α-Alkylation of Ketones: Choice of Base01:10

Factors Affecting α-Alkylation of Ketones: Choice of Base

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α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed by nucleophilic substitution. The choice of base employed is essential as it is the key factor in determining the reaction outcome.
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence,...
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Base-Catalyzed Aldol Addition Reaction01:08

Base-Catalyzed Aldol Addition Reaction

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As depicted in Figure 1, base-catalyzed aldol addition involves adding two carbonyl compounds in aqueous sodium hydroxide to form a β-hydroxy carbonyl compound.
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Relative Strengths of Conjugate Acid-Base Pairs02:29

Relative Strengths of Conjugate Acid-Base Pairs

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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
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The Aufbau Principle and Hund's Rule03:02

The Aufbau Principle and Hund's Rule

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To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and continuing across the periods of the periodic table, we add one proton at a time to the nucleus and one electron to the proper subshell until we have described the electron configurations of all the elements. This procedure is called the aufbau principle, from the German word aufbau (“to build up”). Each added electron occupies the...
72.0K
Parseval's Theorem01:18

Parseval's Theorem

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Parseval's theorem is a fundamental concept in signal processing and harmonic analysis. It asserts that for a periodic function, the average power of the signal over one period equals the sum of the squared magnitudes of all its complex Fourier coefficients. This theorem, named after Marc-Antoine Parseval, provides a powerful tool for analyzing the energy distribution in signals.
Interestingly, Parseval's theorem also holds for the trigonometric form of the Fourier series, which expresses a...
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Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)01:27

Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)

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α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition.
Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon.
Direct addition products are...
4.2K

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Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
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除了基础之外的组成性.

Jean-Charles Pelland1

  • 1University of Bergen, 5015 Bergen, Norway.

Philosophical transactions of the Royal Society of London. Series B, Biological sciences
|October 20, 2025
PubMed
概括

本研究介绍了""作为理解数字基础和构成工具的新框架. 这种以为基础的方法提供了一种更具包容性和准确的方式来讨论不同格式的不同编号系统.

科学领域:

  • 认知科学 认知科学
  • 语言学的语言学.
  • 数学 数学 是一个数学.

背景情况:

  • 在语言学和符号学研究中对数字基础的现有定义是不一致的,阻碍了对数值系统的统一理解.
  • 当前的定义不充分分类多样化的系统,要么排除太多或包括太多的"基础"下.

研究的目的:

  • 提出一个新的概念框架,使用"" (数字作为计数单位) 为编号系统中组成工具的统一理论.
  • 展示现有定义的局限性和以为基础的方法对形式独立分析的优势.

主要方法:

  • 开发一个新的概念框架,以""作为计数单位为中心.
  • 在计数和位置值系统中对感知分组的分析,以说明计数单位和递归单位标签的变化.
  • 应用基于的框架来分析词汇数值系统.

主要成果:

  • 拟议的基于的框架为分类编号系统提供了更具包容性和准确性的方法.
  • 展示了感知分组和位置值系统如何说明框架的核心概念.
  • 突出了框架在分析成熟的词汇系统中的实用性.

结论:

  • 基于的框架为研究编号系统的所有表示格式的组成工具提供了一种优越的,统一的方法.
关键词:
基础 基础 基础 基础 基础构成性的组成性.数字数字数字数字数字数字数字数字数字认知 数字认知这是一个复发复发的复发.单位单位单位单位单位单位.

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  • 该框架解决了现有定义中的不一致性,使得数字基础的讨论更广泛,更准确.
  • 这项研究有助于更深入地了解人类数值认知和表示的基础结构.