Nomenclature of Substituted Benzene Compounds

Introduction

Benzene is an aromatic compound and it has a sweet-smelling odour. It has six C-C bonds. Among these, three C-C bonds are 135 pm length double bonds and another three C-C bonds are 147 pm length single bonds. The shorter C-C distance is for the delocalisation of electrons that is similarly distributed among the carbon atoms. Substituting different functional groups like ketone, alcohol or aldehyde with hydrogen can create different compounds.

What is Benzene?

Benzene is an organic compound, which has six hydrogen atoms and six carbon atoms linked together in a planar ring structure. Due to the cyclic pi bonds between the carbon atoms, it is known as an aromatic hydrocarbon. This hydrocarbon’s chemical formula is C6H6 and its molar mass is 78.114 g per mole.

Figure 1 − Benzene Structure

Benzene is a natural substitute for crude oil. Every hydrogen atom is attached to a carbon atom. Many benzene compounds can be created if we exchange one or more hydrogen compounds with other compounds. The word benzene needs to be added as a suffix after the substituent compound’.

Mono-Substituted Benzene Compounds

In mono-substituted benzene compounds one benzene added to the functional group gets substituted for another compound. The substituent's name gets prefixed to the Benzene. Some names of mono-substituted benzene are the following −

• Methoxybenzene − Anisole is the common name of this compound and its molecular formula is $\mathrm{C_{6}H_{5}OCH_{3}}$.

• Aminobenzene − It is a nitro compound and an $\mathrm{NH_{2}}$ group gets added as a substitute for a hydrogen atom. Aminobenzene is commonly known as aniline and its molecular formula is $\mathrm{C_{6}H_{5}NH_{2}}$.

• Methylbenzene − Methylbenzene also known as toluene has a methyl group that gets added to the benzene. Its molecular formula is $\mathrm{C_{6}H_{5}CH_{3}}$

• Hydroxybenzene − Hydroxybenzene is also known as phenol and its molecular formula is $\mathrm{C_{6}H_{5}OH}$.

• Ethylbenzene − An ethyl group is added to the benzene and creates ethyl benzene. The molecular formula of ethyl benzene is $\mathrm{C_{6}H_{5}CH_{2}CH_{3}}$.

Di-Substituted Benzene Compounds

Di-substituted benzene compounds are the compounds where two substituents are attached to the molecular structure of benzene compounds. In this case, the compound is named in a way that every carbon is attached to the lowest possible numbered compounds.

• 1,3-dinitrobenzene − Here two nitro functional groups got replaced with two hydrogen atoms to form this molecular structure. The nomenclature has been given as 1,3-dinitrobenzene based on lowest carbon atom. Naming it as 1,5- dinitrobenzene would be incorrect as the ratio of the lowest carbon atom distribution will change then.

• 1,3-dichlorobenzene − In this compound, two hydrogen atoms got substituted with two chlorine atoms. The naming has been done by the lowest carbon atom distribution.

Poly-Substituted Benzene Compounds

Poly-substituted benzene compounds are where two or more functional groups get linked in the benzene ring. Any base compound existence in the benzene ring makes it assigned as the number 1. Rest of the compounds get assigned to the lowest carbon atom available for each compound. In the absence of a base group, the compounds get listed in their alphabetical order.

• 1-Bromo-2,4-dinitrobenzene − Here the compounds are placed as per their alphabetical order.

• 3-Chloro-2-nitroaniline − Here aniline is the base compound. That's why it is placed in the number 2 position and chlorine in number 3.

Aromatic Compounds

Aromatic compounds are known as the unusual stability ring structures due to the delocalized pi-electron density. It gets shared among all of the carbon atoms available in the benzene ring. There are various commonly used names for aromatic structures. Those particular names get frequently used instead of IUPAC nomenclature. For example, methylbenzene is known as toluene and dimethyl benzene is known as xylene.

• Aromatic Compound Having a Single Substitute − This type of compound has a single substituent on the ring and the substituent has six or fewer carbons. For example, 1-phenyloctane would be named where the ring is bonded to an 8-carbon chain.

• Aromatic Compound Having Multiple Substitutes − This type of compound has multiple substituents attached to the ring. To name these compounds ortho-, meta-, para-, etc. prefixes can be used followed by the word benzene.

Uses of Benzene

Benzene has various uses in different areas. Some of the common uses of benzene are the following −

• As a Solvent − It is used as a solvent in various commercial, industrial and research projects. It is mostly used in the production stage and helps to manufacture plastic and chemical products. Nylon and styrofoam these products are made with the help of benzene.

Figure 2 − The reaction of the benzyne intermediate with ammonia to form benzenamine

The reaction of the benzyne intermediate with ammonia to form benzenamine, Public domain, via Wikimedia Common

• As an Intermediate − It is also used to produce rubbers and tires. Adhesives that are used to glue soles to shoes also contain benzene. Along with that, it can be used to make detergents, dyes, pesticides, etc

• As a Fuel − It is thoroughly used as a gasoline additive to make it burn more effectively. Due to its natural availability, it is also used individually as a fuel.

• Printing Industry − Benzene is used in printing equipment since it makes the equipment function more effectively and helps it to clean more efficiently.

Conclusion

Despite its various uses, benzene has many health risks. It can cause instability, unconsciousness, headache, convulsions and irritations. It can cause both chronic and acute effects as per the exposure. This can happen if it is absorbed by the skin and inhaled from air or taken through the mouth. Humans are generally exposed to it when using benzene- contained household items or filling the car with fuel or drinking benzene-contaminated water.

FAQs

1. Do cigarettes contain benzene?

The smoke of cigarettes contains benzene. An average smoker inhales 2mg benzene per day compared to 0.2mg/day for non-smokers.

2. Can benzene cause cancer?

Yes, benzene can cause cancer as the disease leukaemia and various other blood diseases are associated with benzene exposure.

3. How can people stay protected from benzene exposure?

Fewer cigarettes, tobacco smoking, and less inhalation of gasoline fumes can decrease the chance of benzene exposure. Factory workers who are exposed to benzene need to take safety measures instructed by the factory itself.