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

芳香族化合物は、共役π結合が環で囲まれた炭化水素です。ベンゼンとその誘導体は、芳香族化合物の最もよく知られた例です。
もともとベンゼン誘導体は、植物や樹木が生産する天然油から分離され、その独特の臭いから「芳香族」と呼ばれていました。
たとえば、アーモンドやチェリーのベンズアルデヒド、トルバルサムのトルエン、クローブのオイゲノールには独特の臭いがあります。
時が経つにつれて、芳香族という用語は、香りがよいかどうかに関係なく、すべてのベンゼン誘導体を説明し続けてきました。たとえば、鎮痛剤のアスピリンには、無臭の芳香族化合物であるアセチルサリチル酸が含まれています。
構造的には、芳香族化合物は非常に不飽和炭化水素であり、アルケン、アルキン、および開鎖ポリエンとは異なる化学的挙動を示します。
単純な芳香族化合物の主な供給源は、コールタールと石油です。
コールタールの分別蒸留では、ベンゼン、トルエン、キシレン、ナフタレンなどの多くの芳香族化合物が得られます。
同様に、石油精製中に、アルカンは芳香族化合物に変換されます。

芳香族化合物: 概要

Aromatic Compounds: Overview

一般に、「芳香」という用語は、生の花、淹れたてのコーヒーなどからの心地よい香りや芳香を指します。有機化学の初期の歴史では、多くのベンゼン誘導体が植物の心地よい香りの油から単離されました。 たとえば、バニリンはバニラ油から、サリチル酸メチルはウィンターグリーン油から、そしてシンナムアルデヒドはシナモン油から単離されました。 どれも心地よい匂いがしていました。 したがって、芳香族という名前が付けられました。

1825 年、ファラデーは圧縮された照明用ガス (ガス灯で燃焼する燃料) からベンゼンを単離し、それを「水素の重炭化水素」と名付けました。 彼はまた、化合物の元素分析を実行し、水素と炭素の比率が 1:1 であることを観察しました。

その後、エイルハルト・ミッチャーリッヒは 1834 年に安息香酸 (ベンゾインゴムから単離) と酸化カルシウムからベンゼンを合成しました。蒸気密度測定を行うことにより、ベンゼンの分子式が C_6H_6 であることを示しました。 この新しい化合物はベンゾインガムから得られたため、彼はそれをベンジン（現在はベンゼンとして知られている）と名付けました。 実験室用溶媒として使用されます。

<img alt="Figure1" src="/files/ftp_upload/12448/12448_PT_Figure_1.svg" style="text-align: center; height: 125px;">

「芳香族」という用語は、芳香の有無にかかわらず、すべてのベンゼン誘導体を表すために今でも使用されています。 天然化合物や医薬品化合物の多くは芳香族です。 たとえば、エストロンはステロイド、アトルバスタチン (リピトール) はコレステロール低下薬、ゾロフトは抗うつ薬、喘息の治療に使用されるセレベントは芳香族化合物です。

<img alt="Figure2" src="/files/ftp_upload/12448/12448_PT_Figure_2.svg" style="text-align: center; height: 425px;">

芳香族化合物は主に石炭と石油から得られます。 石炭は空気のない状態で 1000 °C まで加熱されるとコール タールを生成します。 コールタールは分別蒸留すると、ベンゼン、トルエン、ジメチルベンゼン（キシレン）、ナフタレン、ビフェニル、インデン、アントラセンなどの多くの芳香族炭化水素を生成します。

しかし、芳香族化合物は石油から直接得ることはできません。 石油精製中、アルカンは触媒の存在下、高圧下 500 °C で芳香族化合物に変換されます。

一般に、「芳香族」という用語は、生花、淹れたてのコーヒーなどからの心地よい香りや香りを示します。初期の歴史では...

Education

JoVE Core

Organic Chemistry

有機化学

Unit 1

ユニット1

Aromatic Compounds

芳香族化合物

KEY TERMS AND CONCEPTS

主要用語と概念

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 有機化学では、立体化学、反応、メカニズムの基本概念を、簡潔でわかりやすいアニメーション ビデオ レッスンを使用して説明します。さらに、科学者の実際のビデオでは、世界中の今日の研究室で行われている古典的および独自の研究実験における関連概念の適用を示しています。

Aromatic Compounds in Plants and Fuels

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