谱学证据表明,乙酸在化物H-ββ中存在持久的酸
Morten Bjørgen1, Francesca Bonino, Stein Kolboe
1Department of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway.
Journal of the American Chemical Society
|December 18, 2003
概括
这项研究提供了第一个由热石产生的芳香环质子化的实验证据. 甲基在H-β焦石中的质子化改变了它的振动和电子特性,形成了一个稳定的甲基离子.
科学领域:
- 催化剂是一种催化剂.
- 材料科学 材料科学 材料科学
- 频谱学是一种光谱学.
背景情况:
- 焦岩石是碳化合物转化中的关键催化剂.
- 甲基是酸催化反应中的关键中间体和焦炭前体.
- 对于催化剂设计来说,了解化物内部的分子相互作用至关重要.
研究的目的:
- 为了呈现第一个由泽奥利特产生的芳香环质子化的实验证据.
- 为了研究甲在H-β热中质子化时发生的变化.
- 探索质子化物种的稳定性和影响.
主要方法:
- 红外 (IR) 光谱学用于观察振动性质的变化.
- 紫外线-Vis光谱法用于监测电子过渡.
- 吸附性研究使用H-β热和缺乏质子的模拟物.
主要成果:
- 通过光谱变化证实了甲醇芳香环的质子化.
- 一个新的振动模式在1600厘米-1和一个电子过渡在26000厘米-1出现在质子化.
- 六甲基离子在二氧化腔内保持稳定,温度高达200°C.
结论:
- 热质石可以质子化芳香环,这与基于质子亲和力的预期相反.
- 六甲基离子的稳定性通过焦化石的限制而得到增强.
- 这一发现对了解热酸盐催化过程中的反应机制和焦炭形成有意义.
相关概念视频
Structure of Benzene: Kekulé Model
In 1865, August Kekule suggested the structure of benzene according to the structural theory of organic chemistry based on the three assertions—formula of benzene is C6H6, all the hydrogens of benzene are equivalent, and each carbon must have four bonds due to its tetravalency.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.
Structure of Benzene: Molecular Orbital Model
According to the molecular orbital (MO) model, benzene has a planar structure with a regular hexagon of six sp2 hybridized carbons. As shown in Figure 1, each carbon is bonded to three other atoms with C–C–C and H–C–C bond angles of 120°. The C–H bond length is 109 pm, and the C–C bond length is 139 pm which is midway between the single bond length of sp3 hybridized carbons (154 pm) and sp2 hybridized carbons (133 pm).
Electrophilic Aromatic Substitution: Sulfonation of Benzene
Sulfonation of benzene is a reaction wherein benzene is treated with fuming sulfuric acid at room temperature to produce benzenesulfonic acid. Fuming sulfuric acid is a mixture of sulfur trioxide and concentrated sulfuric acid.
Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
NMR Spectroscopy of Benzene Derivatives
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling constants depend...
Mass Spectrometry: Aromatic Compound Fragmentation
Upon ionization, aromatic compounds generate a molecular ion that is observed as a prominent peak in their mass spectra. For example, the molecular ion peak for benzene appears at a mass-to-charge ratio of 78, while toluene is observed at a mass-to-charge ratio of 92. The molecular ion benzene is highly stable and does not readily undergo further fragmentation due to the significant amount of energy required to disrupt the aromatic stability of the benzene ring. In contrast, the molecular ion...


