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大量の溶解性 (ヘテロ-) アセンの安定化方法

  • 0Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
Journal of the American Chemical Society +

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2024年6月11日

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Stability of Conjugated Dienes 01:28

3.3K

Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.

The two main factors contributing to the enhanced stability of conjugated systems are the delocalization of π electrons and the sp2 hybridization of the carbons forming the single bonds.
Planar Conformers of Conjugated Dienes
Conjugated dienes adopt two planar configurations, s-cis and...

Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration 02:34

8.4K

The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.

The reaction proceeds with the slow protonation of an alkene by a hydronium ion to form a carbocation, which is the rate-determining step.
The reaction involving a tertiary carbocation intermediate is faster than a reaction proceeding through a secondary or primary carbocation. This can be justified by comparing their...

Stability of Substituted Cyclohexanes 02:30

12.6K

This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...

α-Hydroxy Ketones via Reductive Coupling of Esters: Acyloin Condensation Overview 01:19

2.9K

The pinacol and McMurry reactions involve the reductive coupling of ketones or aldehydes. Similarly, the bimolecular reductive coupling of two ester molecules in the presence of sodium metal in an aprotic solvent yields an α-hydroxy ketone product. The α-hydroxy ketone is also called acyloin, so the reaction is referred to as ‘acyloin condensation.’

In the acyloin condensation reaction, esters are converted to ketyls, which undergo radical dimerization to form an unstable...

Preparation of Alkynes: Alkylation Reaction 02:27

10.1K

Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.

The reaction takes place in two steps:
1. The first step is the deprotonation of the terminal alkyne by the strong base forming an acetylide ion.

2. The second step is a nucleophilic...

Relative Stabilities of Alkenes 01:59

13.9K

The relative stability of alkenes can be determined by comparing their heats of hydrogenation. The lower heat of hydrogenation indicates the more stable alkene.  The three main factors determining the relative stability of alkenes are i) the number of substituents attached to the double-bond carbon atoms, ii) hyperconjugation, and iii) the stereochemistry of the double bond.

Number of substituents across the double bond: An alkene with two smaller substituents is more stable than its...