Question

Draw a structural formula for each of the following aromatic compounds. a. 1,2 -dichlorobenzene b. 1,3 -dimethylbenzene c. 3 -nitrophenol d. \(p\) -dibromobenzene e. 4 -nitrotoluene

Short answer

The structural formulas for the given aromatic compounds are: a. 1,2 -dichlorobenzene: Cl | 1-2-3 | | | 6-5-4 H b. 1,3 -dimethylbenzene: CH3 | 1-2-3 | | | 6-5-4 CH3 c. 3 -nitrophenol: OH NO2 | | 1-2-3 | | | 6-5-4 H d. p-dibromobenzene: Br | 1-2-3 | | | 6-5-4 Br e. 4 -nitrotoluene: CH3 | 1-2-3 | | | 6-5-4 NO2

Step-by-step solution

a. 1,2 -dichlorobenzene

1. Draw the benzene ring, which is a hexagon, with alternating single and double bonds between carbon atoms. 2. Number the carbon atoms from 1 to 6. 3. In 1,2 -dichlorobenzene, we have chlorine atoms attached to the 1st and 2nd carbon atoms. Replace the hydrogen atoms in these positions with chlorine atoms. The resulting structure for 1,2 -dichlorobenzene is: Cl | 1-2-3 | | | 6-5-4 H

b. 1,3 -dimethylbenzene

1. Draw the benzene ring with alternating single and double bonds between carbon atoms. 2. Number the carbon atoms from 1 to 6. 3. In 1,3 -dimethylbenzene, we have methyl groups (CH3) attached to the 1st and 3rd carbon atoms. Replace the hydrogen atoms in these positions with methyl groups. The resulting structure for 1,3 -dimethylbenzene is: CH3 | 1-2-3 | | | 6-5-4 CH3

c. 3 -nitrophenol

1. Draw the benzene ring with alternating single and double bonds between carbon atoms. 2. Number the carbon atoms from 1 to 6. 3. In 3 -nitrophenol, we have a hydroxyl group (OH) attached to the 1st carbon atom and a nitro group (NO2) attached to the 3rd carbon atom. Replace the hydrogen atoms in these positions with the respective functional groups. The resulting structure for 3-nitrophenol is: OH NO2 | | 1-2-3 | | | 6-5-4 H

d. p-dibromobenzene

1. Draw the benzene ring with alternating single and double bonds between carbon atoms. 2. Number the carbon atoms from 1 to 6. Since it is para-substituted, the groups are attached to carbon 1 and 4. 3. In p-dibromobenzene, we have bromine atoms attached to the 1st and 4th carbon atoms. Replace the hydrogen atoms in these positions with bromine atoms. The resulting structure for p-dibromobenzene is: Br | 1-2-3 | | | 6-5-4 Br

e. 4 -nitrotoluene

1. Draw the benzene ring with alternating single and double bonds between carbon atoms. 2. Number the carbon atoms from 1 to 6. 3. In 4 -nitrotoluene, we have a methyl group (CH3) attached to the 1st carbon atom and a nitro group (NO2) attached to the 4th carbon atom. Replace the hydrogen atoms in these positions with the respective functional groups. The resulting structure for 4-nitrotoluene is: CH3 | 1-2-3 | | | 6-5-4 NO2

Key concepts

Structural Formula

A structural formula is a graphical depiction of the arrangement of atoms within a molecule. Unlike simple molecular formulas, which tell us only the number and types of atoms present, structural formulas provide detail on the specific connections between atoms. This visual representation is crucial for understanding how different atoms interact and contributes to the overall properties and behavior of the compound.

For example, in the exercise, when drawing 1,2-dichlorobenzene, it's not enough to say that there are six carbons, five hydrogens, and two chlorines in the molecule. The structural formula shows exactly where the chlorine atoms are positioned relative to one another on the hexagonal benzene ring. Thus, structural formulas are essential for conveying the nuances of molecular geometry and for predicting the chemical reactivity of different compounds.

Benzene Ring

The benzene ring is a fundamental component of aromatic compounds, consisting of six carbon atoms arranged in a hexagon and connected by alternating single and double bonds. This pattern of bonds creates a ring of delocalized electrons above and below the plane of the atoms, and is known as resonance. This resonance is key to the stability and unique chemistry of the benzene ring.

The hexagonal shape, combined with the delocalization of electrons, imparts the benzene ring with remarkable chemical stability and a certain level of resistance to reactions that would typically break double bonds. Benzene rings serve as the building blocks for a wide variety of complex organic compounds and are prevalent in both natural and synthetic substances.

Substituted Benzene

Substituted benzene refers to benzene rings that have one or more hydrogen atoms replaced with other atoms or groups of atoms known as substituents. These substituents can significantly influence the chemical properties and reactivity of the benzene ring. The position of substituents on the benzene ring is indicated by numbers or by the terms 'ortho' (adjacent carbons), 'meta' (carbons separated by one carbon), and 'para' (opposite carbons).

When examining compounds like 1,3-dimethylbenzene or p-dibromobenzene, as shown in the exercise, understanding the influence of these substituents on the molecule's properties is crucial. These substitutions can change the polarity, reactivity, and even the physical properties, such as melting or boiling points of the benzene ring. These changes can be predicted through knowledge of the substituents' electronic and steric effects.