一个稳定的碳化合物,1,3-di-tert-butylimidazol-2-ylidene的基本性,在THF中
Yeong-Joon Kim1, Andrew Streitwieser
1Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
Journal of the American Chemical Society
|May 16, 2002
概括
用THF中的碳化合物指标量化了1,3-di-tert-butylimidazol-2-ylidene的基本性. 由于潜在的结效应,这种N-异环碳在DMSO中显著更为基本.
科学领域:
- 有机化学 有机化学
- 物理化学 物理化学
背景情况:
- 在有机金属化学和有机催化中,N-异环碳 (NHC) 是重要的配体.
- 准确测量NHC基本性对于预测它们的反应性和稳定性至关重要.
研究的目的:
- 为了确定1,3-di-tert-butylimidazol-2-ylidene (1) 在四水 (THF) 中的基本性.
- 为了研究离子对和溶液中的自由离子的行为.
- 探索溶剂对NHC基本性的影响.
主要方法:
- 在THF中使用三个碳化合物指标进行基本性测量.
- 确定离子对和自由离子的平衡常数.
- 在THF和二甲基硫氧化物 (DMSO) 中进行光谱分析.
- 一开始的计算建模.
主要成果:
- 在THF中成功测量了1,3-di-tert-butylimidazol-2-ylidene的基本性.
- 观察到离子对和自由离子,并确定它们各自的平衡常数.
- 在THF或DMSO中没有检测到同类结合.
- 与THF相比,碳在DMSO中表现出明显更高的基本性,这归因于结.
结论:
- 1,3-di-tert-butylimidazol-2-ylidene表现出可调节的基本性,受溶剂作用的影响.
- 结合在提高像DMSO这样的极性性溶剂中的质子化NHC的基本性方面发挥着至关重要的作用.
- 计算结果支持关于基本性和溶剂相互作用的实验发现.
相关概念视频
01:16Structure of Conjugated Dienes
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
01:24π Molecular Orbitals of 1,3-Butadiene
Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
01:17Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.
01:23Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
01:28Stability of Conjugated Dienes
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.
01:14Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.