Question

Give structural formulas and systematic names for the three structural isomers of trimethylbenzene, \(\mathrm{C}_{6} \mathrm{H}_{3}\left(\mathrm{CH}_{3}\right)_{3}\)

Short answer

1,2,3-Trimethylbenzene (hemimellitene), 1,2,4-Trimethylbenzene (pseudocumene), 1,3,5-Trimethylbenzene (mesitylene).

Step-by-step solution

Understanding Isomerism

Trimethylbenzene has three methyl groups attached to a benzene ring. The different positions of these methyl groups on the benzene ring give rise to structural isomers. Benzene, with its hexagonal ring structure, has positions for groups numbered 1 to 6. Isomers depend on the relative positions of these groups.

Assigning Positions

In the benzene ring, each carbon atom can hold a methyl group, and we need to place three methyl groups. To find isomers, we consider different possible placements like 1,2,3-trimethyl positions, 1,2,4-trimethyl positions, and so forth. The arrangement of groups will affect the compound's name and structure.

Identifying Isomers

There are three isomers of trimethylbenzene: 1,2,3-trimethylbenzene (vicinal arrangement), 1,2,4-trimethylbenzene (asymmetrical arrangement), and 1,3,5-trimethylbenzene (symmetrical arrangement). Each has a unique arrangement of methyl groups around the benzene ring.

Drawing Structural Formulas

- **1,2,3-Trimethylbenzene (Vicinal Isomer)**: Draw a benzene ring and attach methyl groups to the 1st, 2nd, and 3rd carbon atoms. - **1,2,4-Trimethylbenzene (Asymmetrical Isomer)**: Attach methyl groups to the 1st, 2nd, and 4th carbon atoms. - **1,3,5-Trimethylbenzene (Symmetrical Isomer)**: Attach methyl groups to the 1st, 3rd, and 5th carbon atoms.

Providing Systematic Names

The systematic names follow IUPAC naming conventions: - **1,2,3-Trimethylbenzene** is also known as hemimellitene. - **1,2,4-Trimethylbenzene** is referred to as pseudocumene. - **1,3,5-Trimethylbenzene** is called mesitylene.

Key concepts

Organic Chemistry

Organic chemistry is a branch of chemistry that focuses on the study of carbon-containing compounds. The special thing about organic molecules is that they often include other elements like hydrogen, oxygen, nitrogen, and sometimes halogens. Carbon's ability to form stable bonds with these elements makes the compounds highly diverse and complex.
Trimethylbenzene is an example of an organic compound with a benzene ring as its main feature. Organic chemistry sometimes deals with large and very intricate structures, like those found in living organisms. However, trimethylbenzene is relatively simple, consisting of a core benzene ring with three methyl groups attached.
In organic chemistry, benzene derivatives form a significant part due to their widespread occurrence in natural and synthetic substances. Understanding these structures involves recognizing how carbon atoms interact within rings, allowing them to participate in forming new, stable compounds.

Structural Isomers

In organic chemistry, structural isomers are molecules with the same molecular formula but different structural formulas. This means they have the same number of atoms of each element but arranged differently.
For trimethylbenzene, structural isomers arise by altering the positions of three methyl groups on the benzene ring. These arrangements lead to different compounds, each with unique physical and chemical properties. The concept of isomerism is crucial because it highlights the significance of molecular structure on the behavior of the molecule.
There are three main structural isomers for trimethylbenzene: 1,2,3-trimethylbenzene, which is a vicinal isomer; 1,2,4-trimethylbenzene, known for its asymmetrical arrangement; and 1,3,5-trimethylbenzene, recognized for its symmetrical structure. Understanding these isomers provides insight into how a small change in the position of a group can result in entirely different substances even though they have identical formulae.

Systematic Nomenclature

Systematic nomenclature in organic chemistry refers to the way scientists assign names to compounds according to a standardized set of rules recognized globally. The International Union of Pure and Applied Chemistry (IUPAC) has established these conventions.
The goal is to provide a unique and universally understood name for every compound. For trimethylbenzene isomers, the IUPAC names are based on the positions of the methyl groups on the benzene ring. This includes:

• 1,2,3-Trimethylbenzene, also called hemimellitene
• 1,2,4-Trimethylbenzene, known as pseudocumene
• 1,3,5-Trimethylbenzene, referred to as mesitylene

This naming system helps chemists communicate precisely and avoid confusion. Such clarity is especially important when similar compounds might have very different properties or functions, making unequivocal identification essential.

Benzene Derivatives

Benzene derivatives are organic compounds featuring a benzene ring modified with additional atoms or groups. Benzene itself is a simple cyclic hydrocarbon notable for its stability and aromatic properties.
When other groups attach to the benzene ring, as with trimethylbenzene, the new compounds take on distinctive properties and uses. The methyl groups in trimethylbenzene are examples of alkyl groups, modifying the character of the benzene ring.
These derivatives are integral to many chemical processes and products, often forming the backbone of more complex molecules in dyes, plastics, and pharmaceuticals. The fascinating aspect of benzene derivatives is the endless possibility for creating new substances simply by changing the nature and positions of the attached groups, thus influencing the compound's overall properties and potential applications.