Name: aromatic compounds in plants and fuels
Uploaded: 2023-04-30T10:30:40.000Z
Duration: 1 min 25 s
Channel: JoVE

芳香族化合物是环状结构中带有共轭π键的烃类。苯及其衍生物是最常见的芳香族化合物。
最初，苯的衍生物是从植物和树木产生的天然油中分离得到的，因其独特的气味而被称为“芳香的”。
例如，来自杏仁和樱桃的苯甲醛、来自吐鲁香脂的甲苯以及来自丁香的丁香酚具有不同的气味。
随着时间的推移，“芳香”一词一直用于描述所有苯的衍生物，而不论它们是否具有香味。例如，止痛药阿司匹林含有乙酰水杨酸，这是一种无气味的芳香族化合物。
从结构上看，芳香族化合物是高度不饱和的烃类，其化学性质与烯烃、炔烃和开链多烯烃不同。
简单芳香族化合物的主要来源是煤焦油和石油。
煤焦油的分馏可得到多种芳香族化合物，例如苯、甲苯、二甲苯、萘等。
类似地，在石油精炼过程中，烷烃被转化为芳香族化合物。

芳香族化合物:概述

Aromatic Compounds: Overview

一般来说，"芳香"一词是指来自鲜花、现煮咖啡等的令人愉悦的气味或香味。在有机化学早期历史中，许多苯衍生物都是从气味宜人的植物油中分离出来的。 例如，香草醛是从香草油中分离出来的，水杨酸甲酯是从冬青油中分离出来的，肉桂醛是从肉桂油中分离出来的。 它们都有一种令人愉悦的气味。 因此命名为"芳香"。


 1825 年，法拉第从压缩照明气体（煤气灯中燃烧的燃料）中分离出苯，并将其命名为"氢的碳化物"。 他也对该化合物进行了元素分析，并观察到氢与碳的比例为 1:1。


 后来，Eilhardt Mitscherlich于1834年用苯甲酸（从安息香胶中分离出来）和氧化钙合成了苯。通过进行蒸气密度测量，他表明苯的分子式为C6H6。 由于这种新化合物是从安息香胶中提炼出来的，因此他将其命名为Benzin，即现在的苯。 它用作实验室溶剂。

 <img alt="Figure1" src="/files/ftp_upload/12448/12448_PT_Figure_1.svg" style="text-align: center; height: 125px;">

 "芳香族"一词仍然用于描述所有苯衍生物，无论是否芳香。 许多天然化合物和药物化合物都是芳香族的。 例如，雌酮是一种类固醇，阿托伐他汀（立普妥）是一种降胆固醇药物，左洛复是一种抗抑郁药，而用于治疗气喘的塞万特，都是芳香族化合物。

 <img alt="Figure2" src="/files/ftp_upload/12448/12448_PT_Figure_2.svg" style="text-align: center; height: 425px;">

 芳香族化合物主要从煤和石油中获得。 煤在没有空气的情况下加热到 1000 °C 时会产生煤焦油。 煤焦油经分馏可获得苯、甲苯、二甲苯、萘、联苯、茚、蒽等多种芳香烃。


 然而，芳香族化合物不能直接从石油中获得。 在石油精炼过程中，烷烃在催化剂存在下在 500 °C 的高压下转化为芳香化合物。

通常，“芳香”一词指来自鲜花、现煮咖啡等的新鲜气味或香味。在早期历史中……

Education

教育

JoVE Core

Organic Chemistry

有机化学

Unit 1

第一单元

Aromatic Compounds

芳香族化合物

KEY TERMS AND CONCEPTS

关键术语与概念

aromatic compounds in plants and fuels

Aromatic compounds are linked to both pleasant smells and important chemical structures. The word aromatic first came from fragrant natural sources such as fresh flowers and spices. Early organic chemists isolated benzene derivatives from oils of plants, including vanillin from vanilla, methyl salicylate from wintergreen, and cinnamaldehyde from cinnamon.

The history of benzene also helped shape the idea of aromatic compounds. In 1825, Faraday isolated benzene from compressed illuminating gas, which was used in gaslights. He called it bicarburet of hydrogen and found a 1:1 ratio of hydrogen to carbon. In 1834, Eilhardt Mitscherlich made benzene from benzoic acid, which comes from gum benzoin, and calcium oxide. He used vapor density measurements to show that benzene has the formula C6H6, and he named it Benzin, now called benzene.

Today, the term aromatic includes many benzene derivatives, even when they do not smell pleasant. Benzene itself is used as a laboratory solvent. Many natural and pharmaceutical compounds are aromatic, including estrone, atorvastatin (Lipitor), Zoloft, and Serevent.

Aromatic compounds are mainly obtained from coal and petroleum. When coal is heated to 1000 °C without air, it forms coal tar. Fractional distillation of coal tar gives aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene, biphenyl, indene, and anthracene. Aromatic compounds are not taken directly from petroleum, but petroleum refining can convert alkanes into aromatic compounds with a catalyst at 500 °C under high pressure.

Aromatic Compounds in Plants and Fuels

aromatic compounds: overview

Aromatic compounds are linked to both pleasant smells and important chemical structures. The word aromatic first came from fragrant natural sources such as fresh flowers and spices. Early organic chemists isolated benzene derivatives from oils of plants, including vanillin from vanilla, methyl salicylate from wintergreen, and cinnamaldehyde from cinnamon. The history of benzene also helped shape the idea of aromatic compounds. In 1825, Faraday isolated benzene from compressed illuminating gas,...

nomenclature of aromatic compounds with a single substituent

nomenclature-of-aromatic-compounds-with-a-single-substituent

Naming Benzene Derivatives with One Group

Benzene derivatives with one substituent are named by attaching the substituent name to benzene. Benzene is the simplest aromatic hydrocarbon, also called an arene. For simple monosubstituted benzene compounds, IUPAC naming uses the group name as a prefix. Halogen-substituted benzene compounds follow this pattern. The halogen prefix can be fluoro, chloro, bromo, or iodo. When an alkyl group is attached to the benzene ring, the name depends on the chain length of that group. If the alkyl chain...

nomenclature of aromatic compounds with multiple substituents

nomenclature-of-aromatic-compounds-with-multiple-substituents

Naming Benzene Rings with Multiple Groups

Naming benzene rings with multiple groups depends on how many substituents are attached. For benzene derivatives with two groups, three constitutional isomers are possible. The position of each group is described with IUPAC naming rules. For disubstituted benzene compounds, the relative positions can be shown with ortho, meta, and para. These terms are also written as o, m, and p. They can also be written with numbers, such as 1,2- for ortho, 1,3- for meta, and 1,4- for para. Dimethyl benzene,...

structure of benzene: kekul&eacute; model

Kekule’s Benzene Model and Its Limits

Kekule’s benzene model describes benzene as a six-carbon ring with alternating pi bonds. August Kekule proposed this structure in 1865 from the formula C6H6, the idea that all benzene hydrogens are equivalent, and the rule that each carbon has four bonds because of tetravalency. In this model, each carbon is attached to one hydrogen atom. It also predicts two isomers for 1,2-disubstituted benzene derivatives. In one form, the substituted carbons are linked by a double bond, and in the other...

structure of benzene: molecular orbital model

structure-of-benzene-molecular-orbital-model

Benzene π Orbitals and Electron Delocalization

Benzene has a planar ring structure with delocalized π electrons. Its six carbon atoms form a regular hexagon, and each carbon is sp2 hybridized. The C–C–C and H–C–C bond angles are 120°, which matches the flat shape of the ring. Each carbon is bonded to three other atoms. The C–H bond length is 109 pm, and the C–C bond length is 139 pm. That C–C distance is midway between the single bond length of sp3 hybridized carbons, 154 pm, and the sp2 value, 133 pm. Beneath and above the ring plane,...

criteria for aromaticity and the h&uuml;ckel 4n + 2 rule

criteria-for-aromaticity-and-the-hckel-4n-2-rule

H&uuml;ckel Rule and Aromatic Ring Criteria

Aromatic rings follow H&amp;uuml;ckel’s rule, also called the 4n + 2 rule. This rule helps identify which unsaturated cyclic compounds are aromatic and why some ring systems are unstable instead. Benzene is the classic example, while cyclobutadiene and cyclooctatetraene show different behavior and are not aromatic. Eric H&amp;uuml;ckel, a German chemical physicist, first described the structural features needed for aromaticity. An aromatic compound must be cyclic, planar, and continuously...

h&uuml;ckel's rule diagram of &pi; mos: frost circle

Frost Circle for Pi Orbital Energies

The Frost circle is a graphical method for showing the relative energies of pi molecular orbitals in planar, fully conjugated, monocyclic compounds. It is also called the inscribed polygon method. A. A. Frost and Boris Musulin first described this method in 1953. To build a Frost circle, draw a polygon with the same number of edges as the number of carbons in the cyclic system. Place one vertex pointing downward. Then draw a circle around the polygon so that every vertex touches the circle.

frost circles for different conjugated systems

frost-circles-for-different-conjugated-systems

Using Frost Circles to Test Aromaticity

Frost circles help test whether a cyclic compound is aromatic by using the inscribed polygon method and Hückel’s 4n + 2 rule. A compound is stable and aromatic when every bonding molecular orbital (MO) is completely filled with a pair of electrons. If electrons occupy non-bonding or antibonding orbitals, the compound is unstable and not aromatic. Frost circle diagrams for cycloalkenes with 4 to 8 carbons show a clear pattern. The number of bonding MOs is always odd. The electrons needed to...

aromatic hydrocarbon anions: structural overview

aromatic-hydrocarbon-anions-structural-overview

Cyclopentadienyl Anion and Aromaticity

Cyclopentadiene is a neutral hydrocarbon that is not aromatic. It contains an odd number of carbon atoms and one CH2 group in the ring. With only 4 pi electrons, it does not follow the 4n + 2 pi electron rule. The CH2 carbon is sp3 hybridized, so it has no vacant p orbital to keep p orbitals overlapped around the ring. That break in overlap stops pi electrons from spreading across the entire ring. As a result, cyclopentadiene does not meet the usual aromaticity criteria. If one hydrogen is...

aromatic hydrocarbon cations: structural overview

aromatic-hydrocarbon-cations-structural-overview

Cycloheptatrienyl Cation and Aromaticity

Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon with seven carbon atoms. One carbon in the ring is sp3 hybridized, which breaks the continuous overlap of p orbitals. Even though the ring has three double bonds and 6 π electrons, cycloheptatriene is not aromatic because the p orbitals do not form one uninterrupted loop. Removing one hydrogen from the CH2 group changes the ring. If that hydrogen is removed with both, one, or no electrons, the products are the cycloheptatrienyl...

five-membered heterocyclic aromatic compounds: overview

five-membered-heterocyclic-aromatic-compounds-overview

Five-Membered Aromatic Rings with Heteroatoms

Five-membered aromatic rings with heteroatoms are cyclic compounds that contain one or more atoms other than carbon in the ring. They are aromatic and can have either five or six atoms in the ring. Common examples include pyrrole, furan, thiophene, and imidazole. These rings differ by the heteroatom present. Pyrrole has one nitrogen atom with one lone pair of electrons. Furan has one oxygen atom, and thiophene has one sulfur atom. Both furan and thiophene have two lone pairs of electrons.

nmr spectroscopy of aromatic compounds

Aromatic Ring Shifts in NMR Spectra

Aromatic ring shifts in NMR spectra help identify aromatic compounds using proton NMR and carbon-13 NMR. Aromatic hydrogens are often strongly deshielded by the aromatic ring current, so they usually appear in the 6.5–8.0 ppm range in proton NMR. In benzene, the hydrogens directly bonded to the ring absorb at 7.3 ppm. Larger aromatic rings can place hydrogens outside the usual range. In [18]annulene, the 12 outer hydrogens are highly deshielded by the ring current and absorb downfield at 9.3...

key terms and concepts

Explore how aromatic compounds were first found in plant oils, how benzene was identified, and how coal tar and petroleum produce key aromatic hydrocarbons.

Aromatic Compounds in Plants and Fuels | JoVE K12

organic chemistry

JoVE Core 有机化学（Organic Chemistry）使用简明易懂的动画视频课程解释立体化学、反应和机制的基本概念。 此外，科学家在行动视频展示了相关概念在当今世界各地实验室进行的经典和原创研究实验中的应用。

Aromatic Compounds in Plants and Fuels

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