违反规则:关于某些甲基和甲基衍生物的相对稳定性
Delio Santalucia1, Mattia Bondanza1, Filippo Lipparini1
1Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via G. Moruzzi 13, 56126, Pisa, Italy.
Chemistry (Weinheim an der Bergstrasse, Germany)
|March 14, 2024
概括
这项研究表明,螺旋环产品是2-甲基cyclopropenes (MeCP),而不是2-甲基cyclopropanes (MCP). 计算分析表明MeCP更稳定,挑战了关于不和环烯衍生物的现有信念.
科学领域:
- 有机化学 有机化学
- 计算化学计算化学
- 结构化学 结构化学
背景情况:
- 之前的研究报告了螺旋环产品作为2-甲基烯cyclopropane (MCP) 衍生物.
- 不和环烯衍生物通常偏好甲基环烯 (MCP) 异构体.
研究的目的:
- 阐明从甲基醇和1,1-二二二甲基) cyclopropane的螺旋环产品的正确结构.
- 为了研究2 - 甲基cyclopropene (MeCP) 和MCP异构体之间的热力学稳定性和平衡.
- 了解影响MeCP与MCP在特定系统中的意外稳定性的因素.
主要方法:
- 核磁共振 (NMR) 光谱学 核磁共振 (NMR) 光谱学
- 在X射线晶体学.
- 密度函数理论 (DFT) 的计算.
- 结合集群的单一,双重和扰动性三重激发 (CCSD ((T)) 计算.
- 实验性的平衡研究研究.
主要成果:
- 螺旋环产品被证实是2-甲基cyclopropene (MeCP) 衍生物,与此前的报告相反.
- 发现MeCP异构体比MCP异构体稳定大约2.5-3.0 Kcal/mol.
- 电子和环应变效应被确定为推动意想不到的平衡转向MeCP的关键因素.
结论:
- 这一类化合物的已确立的结构分配需要修订.
- MeCP异构体的意想不到的稳定性挑战了不和环烯化学中长期存在的假设.
- 这些发现需要重新评估相关系统中的结构稳定性关系.
相关概念视频
Stability of Substituted Cyclohexanes
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...
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...
12.6K
Conformations of Cycloalkanes
11.8K
Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3 hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that...
11.8K
Disubstituted Cyclohexanes: cis-trans Isomerism
11.9K
Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
11.9K
Mass Spectrometry: Cycloalkane Fragmentation
1.4K
In mass spectrometry, cycloalkanes exhibit distinct fragmentation patterns due to the inherent stability of their molecular ions compared to linear or branched alkanes. The ring structure of cycloalkanes provides additional stability to the molecular ions, often resulting in prominent ion peaks in the mass spectrum.
For example, cyclohexane molecular ions have a mass-to-charge ratio (m/z) of 84, which tends to produce a stronger signal than linear alkanes like hexane. This stability comes from...
For example, cyclohexane molecular ions have a mass-to-charge ratio (m/z) of 84, which tends to produce a stronger signal than linear alkanes like hexane. This stability comes from...
1.4K
Stereoisomerism of Cyclic Compounds
8.8K
In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
8.8K
Stability of Conjugated Dienes
3.4K
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.
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.
3.4K


