Question

Draw the structure of 1,4 -dichlorobenzene. Which of its properties make it useful as an insecticide?

Short answer

1,4-Dichlorobenzene has a para-substituted benzene ring with chlorine atoms and its vapors are toxic to insects, useful for pest control.

Step-by-step solution

Understand the Benzene Ring

Benzene is a hydrocarbon with a ring structure consisting of six carbon atoms connected by alternating single and double bonds, denoted as a hexagon with alternating double lines.

Identify Substituent Positions

Since the compound is 1,4-dichlorobenzene, two chlorine atoms are attached to the benzene ring at carbon positions 1 and 4. This means that the chlorine atoms are opposite each other on the benzene ring, or in para position.

Draw the Structural Formula

First, draw a hexagon to represent the benzene ring with alternating double bonds. Label a carbon as the first position. Then, on carbon 1, attach a chlorine atom (Cl). Directly opposite, on carbon 4, attach another chlorine atom (Cl).

Describe the Useful Properties

1,4-dichlorobenzene has notable properties like low volatility, a strong odor, and sublimation capability. Its aryl halide structure allows it to be a solid at room temperature and release vapors that are toxic to moths and insects, making it an effective insecticide.

Key concepts

Benzene Ring Structure

The benzene ring is a core element of aromatic chemistry. It's a unique structure characterized by six carbon atoms arranged in a hexagonal shape. Each carbon atom forms

• one bond with a hydrogen atom,
• making a total of six hydrogen atoms,
• and engages in alternating single and double bonds with its neighboring carbon atoms.

This alternating pattern of bonds can be visualized as a circle within the hexagon, symbolizing the equal electron distribution and resonance stabilization of the benzene ring. This resonance gives benzene its remarkable stability and makes it a parent compound for many derivatives, such as 1,4-dichlorobenzene. The benzene ring's ability to accommodate derivatives makes it important in the study of organic chemistry.

Aryl Halides

Aryl halides are a category of organic molecules where a halogen atom is directly connected to an aromatic ring, such as benzene. These connections entail an important substitution reaction where a hydrogen atom on the benzene is replaced by a halogen like chlorine, fluorine, bromine, or iodine. 1,4-dichlorobenzene exemplifies an aryl halide where two chlorine atoms substitute benzene hydrogens on carbon positions 1 and 4 of the ring. The chlorination of benzene creates unique physicochemical properties:

• Increased chemical reactivity compared to benzene alone due to the presence of electronegative halogens,
• Solubility and boiling point modifications, providing practical applications in industry and laboratories.

Sublimation

Sublimation is the process by which a substance transitions directly from a solid state to a gas, bypassing the liquid phase. In the context of chemistry and everyday encounters, sublimation is less common but distinct. For 1,4-dichlorobenzene, sublimation is a notable property. This compound at room temperature can emit vapors directly from its solid form, allowing it to function effectively as an insecticide without dissolving. This property is harnessed in household settings where 1,4-dichlorobenzene helps maintain freshness and insect control, often in the form of mothballs. Sublimation enhances its efficacy as it releases high concentrations of the compound into the air efficiently.

Insecticide Properties

1,4-Dichlorobenzene is mainly used as an insecticide owing to its effective vapor-phase action. Its efficacy lies in the following properties:

• Its strong odor deters moths and other pests, protecting clothes and fabrics from insect damage.
• Sublimation allows it to consistently release pest-repellent vapors without the need for dilution in water or other solvents.
• The compound is solid at room temperature, which simplifies its handling and allows safe, long-term storage in closets and wardrobes.

The low volatility ensures a steady release of active vapors over time, making it a reliable choice for household pest control, especially for closed environments. These properties link directly to its chemical structure and physical characteristics derived from the benzene ring's aromaticity and halogen substitution.