Question

Draw structural formulas for the following compounds: (a) 1,3 -dichlorobenzene (alternatively called \(m\) -dichlorobenzene) (b) 1-bromo-4-methylbenzene (alternatively called \(p\) -bromotoluene)

Short answer

1,3-dichlorobenzene has Cl atoms at meta positions; 1-bromo-4-methylbenzene has Br and CH₃ at para positions.

Step-by-step solution

Understanding the Structure of Benzene

Benzene is a six-carbon ring compound with alternating double bonds. The carbons form a hexagonal structure, with hydrogen atoms attached to each carbon. The formula is often denoted as a hexagon with a circle inside, representing the delocalized electrons.

1,3-Dichlorobenzene Structure

For 1,3-dichlorobenzene, substitute two hydrogen atoms with chlorine atoms on the benzene ring. The numbers 1 and 3 indicate the positions of chlorine substitutes in relation to one another, meaning they are positioned either next to each other and connected by an arc (meta position).

Drawing 1,3-Dichlorobenzene

Start with the benzene ring. Place the first chlorine (Cl) atom on a carbon, which will be designated as carbon 1. Move two positions away (counting the next adjacent carbon as position 2) to position 3, placing the second chlorine (Cl) atom.

1-Bromo-4-Methylbenzene Structure

For 1-bromo-4-methylbenzene, the bromine atom and methyl group are attached to the benzene ring. The numbers 1 and 4 indicate para positions, meaning the substituents are opposite each other on the benzene ring.

Drawing 1-Bromo-4-Methylbenzene

Start with the benzene ring. Place a bromine (Br) atom on position 1. Move counter or clockwise to the opposite side, position 4, to place the methyl group (CH₃).

Key concepts

Benzene Structure

Benzene is one of the most fundamental components in organic chemistry. It's fascinating due to its unique structure that offers stability and reactivity due to electron delocalization. This compound is a six-carbon ring, shaped as a hexagon, where each carbon atom is bonded to a hydrogen atom. The key aspect of benzene is its alternating double bonds, but in reality, benzene's electrons are delocalized. This means they are shared across the entire structure, giving benzene its characteristic stability and properties.

Often, benzene is depicted as a hexagonal ring with a circle inside it. This circle represents the delocalized electrons. This simple yet elegant structure is what allows benzene to serve as a parent molecule for many aromatic compounds.

Substituent Positioning

Understanding substituent positioning on a benzene ring is crucial in organic chemistry. A substituent can be any atom or group of atoms that replace a hydrogen atom on a benzene ring.

• Ortho (o-) position: Substituents are adjacent to each other.
• Meta (m-) position: Substituents are separated by one carbon atom in between.
• Para (p-) position: Substituents are directly opposite each other across the benzene ring.

In the context of this exercise, for example, 1,3-dichlorobenzene, the '1,3' indicates a meta positioning, where two chlorine atoms are positioned with one carbon atom in between on the benzene ring. Conversely, in 1-bromo-4-methylbenzene, the '1,4' signifies a para positioning where the substituents (bromine and methyl) are directly opposite one another.

Structural Formulas

Drawing structural formulas accurately is fundamental in organic chemistry. Structural formulas illustrate how the atoms within a molecule are bonded and arranged, as seen with benzene derivatives.

When drawing benzene with substituents, start with the hexagonal ring. Place each substituent according to its specific positional nomenclature. For instance, if you have a meta position, place the first substituent at position 1, and move two positions away for the second substituent.

In the case of para positioning, start at the carbon marked as 1, and place the second substituent directly across at position 4. Precision with these diagrams is key, as they provide a clear view of the molecular structure and relationships among the atoms involved.

Aromatic Compounds

Aromatic compounds are a fascinating class of organic molecules, and benzene is at the heart of this category. Aromatic compounds are defined by their ring-like structure with conjugated pi electrons, much like benzene with its delocalized electrons.

Such compounds exhibit aromaticity, a unique stability attributed to their electronic structure. This property makes aromatic compounds less reactive than alkenes but still very crucial in chemical reactions, especially in substitution reactions where one hydrogen atom can be replaced by another group, forming derivatives like those seen in this exercise.

• Aromatic compounds commonly feature in many applications, ranging from pharmaceuticals to dyes and fragrances.
• They are essential in both industrial and synthetic chemical processes.

Understanding the basic properties and structure of aromatic compounds offers insight into their widespread use and significance in various chemical landscapes.