Question

How many different possible "tetramethylbenzenes" exist? Provide structural formulas and names for each.

Short answer

Three different tetramethylbenzenes exist, including their structural formulas and names: 1. 1,2,3,4-tetramethylbenzene: \[ \chemfig{*6((-!{CH_3})=(-!{CH_3})-(-!{CH_3})=(-!{CH_3})=-=)} \] 2. 1,2,3,5-tetramethylbenzene: \[ \chemfig{*6((-!{CH_3})=(-!{CH_3})-(-!{CH_3})=(-)-(!{CH_3})=)} \] 3. 1,2,4,6-tetramethylbenzene: \[ \chemfig{*6((-!{CH_3})=(-!{CH_3})-(-)-(!{CH_3})=(!{CH_3})-)} \] These are the unique structures that can be formed by adding four methyl groups to the benzene ring at different positions considering symmetry and ortho, meta, and para substitutions.

Step-by-step solution

1. Identify and draw the benzene ring

First, draw the basic benzene ring structure, which consists of six carbon atoms in a hexagon with alternating single and double bonds. \[ \chemfig{*6(=-=-==-)} \]

2. Add the methyl groups at different positions

Now, we will add the four methyl groups to the benzene ring. We must consider the symmetry and differences in positions. Remember, we are using ortho (o-), meta (m-), and para (p-) prefixes to indicate relative positions. We must pay close attention to the number of unique possible combinations.

3. Draw the first possible tetramethylbenzene

Add all four methyl groups at o- positions: \[ \chemfig{*6((-!{CH_3})=(-!{CH_3})-(-!{CH_3})=(-!{CH_3})=-=)} \] This is called 1,2,3,4-tetramethylbenzene.

4. Draw the second possible tetramethylbenzene

Add three methyl groups at o- positions and one at m- position: \[ \chemfig{*6((-!{CH_3})=(-!{CH_3})-(-!{CH_3})=(-)-(!{CH_3})=)} \] This is called 1,2,3,5-tetramethylbenzene.

5. Draw the third possible tetramethylbenzene

Add two methyl groups at o- positions, one at m- position, and one at p- position: \[ \chemfig{*6((-!{CH_3})=(-!{CH_3})-(-)-(!{CH_3})=(!{CH_3})-)} \] This is called 1,2,4,6-tetramethylbenzene.

6. Identify the total number of tetramethylbenzenes and review

Three different tetramethylbenzenes exist: 1,2,3,4-tetramethylbenzene, 1,2,3,5-tetramethylbenzene, and 1,2,4,6-tetramethylbenzene. These are the unique structures that can be formed by adding four methyl groups to the benzene ring at different positions considering symmetry and ortho, meta, and para substitutions.

Key concepts

Aromatic Compounds

In organic chemistry, aromatic compounds hold a special place due to their distinct structure and properties. These compounds typically contain one or more benzene rings. Benzene, a key aromatic compound, has a stable ring structure with alternating single and double bonds.

Aromatic compounds are known for their aromaticity, a concept characterized by delocalized electrons within the ring leading to increased stability. This stability is explained by resonance, a phenomenon where electrons are shared between different pi bonds.

• Benzene is a classic example of an aromatic compound.
• Aromatic compounds often have pleasant smells, hence their name.
• The stability is due to the pi-electron cloud above and below the carbon ring.

Structural Isomers

Structural isomers are molecules that have the same molecular formula but different structural formulas. This means that even though the number and type of atoms are the same, the connectivity between them differs, resulting in unique compounds with different properties.

In the context of tetramethylbenzene, structural isomers arise from the different possible positions of methyl groups around the benzene ring.

• Isomers can vastly differ in physical and chemical properties.
• The different positions of methyl groups lead to different compounds.
• For example, 1,2,3,4-tetramethylbenzene differs from 1,2,3,5-tetramethylbenzene due to the placement of methyl groups.

Tetramethylbenzene

Tetramethylbenzene is a compound derived from benzene where four hydrogen atoms have been replaced by four methyl groups (\(CH_3\)). The challenge is to determine how these groups can be arranged uniquely around the benzene ring.

The three isomers of tetramethylbenzene—1,2,3,4-tetramethylbenzene, 1,2,3,5-tetramethylbenzene, and 1,2,4,6-tetramethylbenzene—demonstrate the principle of structural isomerism. Each arrangement creates a distinct structure.

• 1,2,3,4-tetramethylbenzene has methyl groups on four consecutive carbon atoms.
• 1,2,3,5-tetramethylbenzene features three successive groups and one that skips a position.
• 1,2,4,6-tetramethylbenzene spaces its methyl groups more evenly.

Benzene Ring

The benzene ring is a fundamental feature in aromatic compounds, consisting of a six-carbon ring with alternating single and double bonds, often depicted as a hexagon with a circle in the center. This ring is not just a series of alternating bonds; it is a delocalized structure. Delocalization means that the electrons are shared equally among the six carbon atoms, contributing to benzene's remarkable stability and its planar, symmetrical shape.

Understanding the benzene ring is crucial for grasping the nature of aromatic compounds and the implications of structural modifications like those in the formation of tetramethylbenzene isomers.

• The benzene ring is a model of resonance stability.
• All carbon-carbon bonds have uniform lengths, intermediate between single and double bonds.
• Substitutions on the benzene ring, such as adding methyl groups, lead to different isomeric forms.