Question

How is a monosubstituted benzene named? Give the structures and names of two examples. Also give two examples of monosubstituted benzenes that have special names.

Short answer

A monosubstituted benzene is named based on the functional group replacing one hydrogen atom on the benzene ring. Two examples: 1) Methylbenzene (toluene), with the structure \(\ce{C6H5-CH3}\), where the methyl group replaces one hydrogen. 2) Chlorobenzene, with the structure \(\ce{C6H5-Cl}\), where chlorine replaces one hydrogen. Two monosubstituted benzenes with special names are phenol (hydroxybenzene) with the structure \(\ce{C6H5-OH}\) and aniline (aminobenzene) with the structure \(\ce{C6H5-NH2}\).

Step-by-step solution

Understanding monosubstituted benzene

Monosubstituted benzene is a benzene molecule with one hydrogen atom replaced by another functional group. The name of the monosubstituted benzene is derived from the name of the functional group attached to the benzene ring.

Example 1 - Methylbenzene

In methylbenzene, one hydrogen atom of the benzene ring is replaced by a methyl group (CH3). The structure of methylbenzene is: \[ \ce{C6H5-CH3} \] Methylbenzene is also known as toluene.

Example 2 - Chlorobenzene

In chlorobenzene, one hydrogen atom of the benzene ring is replaced by a chlorine atom (Cl). The structure of chlorobenzene is: \[ \ce{C6H5-Cl} \] Chlorobenzene is the name used to refer to this compound.

Special name example 1 - Phenol

Phenol is a monosubstituted benzene with a special name. In phenol, one hydrogen atom of the benzene ring is replaced by a hydroxyl group (OH). The structure of phenol is: \[ \ce{C6H5-OH} \] Phenol is also known as hydroxybenzene or benzenol.

Special name example 2 - Aniline

Aniline is another monosubstituted benzene with a special name. In aniline, one hydrogen atom of the benzene ring is replaced by an amino group (NH2). The structure of aniline is: \[ \ce{C6H5-NH2} \] Aniline is also known as aminobenzene or benzeneamine.

Key concepts

IUPAC nomenclature of organic compounds

The International Union of Pure and Applied Chemistry (IUPAC) nomenclature is a systematic method of naming organic chemical compounds as recommended by the IUPAC. Its goal is to ensure that each chemical compound has a unique and unambiguous name, and to provide a standardized way to refer to structures, especially when drawing or discussing chemical reactions.

For monosubstituted benzenes, the IUPAC name is formed by stating the name of the substituent followed by the word 'benzene'. If the substituent has a specific common name, the common name can be used in lieu of the systematic one. An example of this is methylbenzene, which is commonly known as toluene. In the case of multiple substituents, a number is used to indicate the position of each substituent on the benzene ring, following the order of priority or alphabetization.

Functional groups in organic chemistry

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They play a key role in the chemistry of life and organic chemical reactions. In organic chemistry, functional groups define the structure of families of compounds and dictate how they behave under different chemical conditions.

The presence and identity of functional groups can dramatically modify the properties of the base hydrocarbon, benzene, in this case. For example, a hydroxyl group (-OH) transforms benzene into phenol, which exhibits different properties compared to the parent compound. Substituents like chloro (-Cl), methyl (-CH3), nitro (-NO2), and amino (-NH2) are common functional groups that define a range of benzene derivatives.

Benzene derivatives

Benzene derivatives are compounds that contain a benzene ring as their core structural feature, but with one or more hydrogen atoms replaced by other atoms or groups of atoms—these are the 'substituents' that define the specific derivative. These derivatives, which can also be referred to as 'aromatic compounds', have a wide range of applications in both industrial and pharmaceutical settings due to their diverse physical and chemical properties.

Some monosubstituted benzene compounds have special names that are exceptions to the typical naming conventions. Phenol and aniline are examples of this, with phenol being a benzene ring with a substituent hydroxyl group (-OH) and aniline being a benzene ring with an amino group (-NH2).

Chemical structure representation

Chemical structure representation is vital for understanding and communicating the specific arrangement of atoms within a molecule. Organic molecules can be represented in different ways, but the most common is the structural formula, which shows the framework of bonds between atoms and the positions of functional groups.

For monosubstituted benzene compounds, the structure is represented by drawing the hexagonal benzene ring with a circle in the middle to denote the delocalized pi electrons, and then adding the substituent at the appropriate position. For instance, toluene is drawn with a methyl group attached to the ring, while aniline has an amino group. These visual representations are crucial for understanding molecular geometry, predicting the behavior of molecules in reactions, and for synthetic planning in the lab.