Question

Write structural formulas for the following compounds. (a) 2,5 -dichloro-1-ethylbenzene (b) 2 -ethyl-1,3-dimethylbenzene

Short answer

The structural formulas for the two given compounds are as follows: 2,5 -dichloro-1-ethylbenzene has an ethyl group at carbon 1, and chlorine atoms at carbon 2 and 5 of the benzene ring. 2 -ethyl-1,3-dimethylbenzene has an ethyl group at carbon 2, and methyl groups at carbon 1 and 3 of the benzene ring.

Step-by-step solution

Visualize the Benzene ring

Firstly, visualize a benzene ring which consists of six carbon atoms arranged in a hexagonal ring, with three double bonds. Each carbon atom in the benzene ring is also bonded to one hydrogen atom, but this can be replaced by the substituents according to their positions given in the problem.

Assign the Position for First Compound

For the first compound 2,5 -dichloro-1-ethylbenzene, begin by attaching the ethyl group to the first carbon atom. Then attach a chlorine atom to the second and fifth carbon atoms, respectively. Ensure that you maintain the cyclic structure of benzene.

Draw the Structure for First Compound

Now draw the structure with a hexagonal benzene ring, marked by alternating double bonds. At the first carbon position, draw an ethyl group (C2H5). At the second and fifth positions, draw a chlorine atom (Cl). This completes the structural formula for 2,5-dichloro-1-ethylbenzene.

Assign the Position for Second Compound

For the second compound 2 -ethyl-1,3-dimethylbenzene, begin by attaching the ethyl group to the second carbon atom. Then attach a methyl group to the first and third carbon atoms, respectively. Here too, ensure you maintain the cyclic structure of benzene.

Draw the Structure for Second Compound

Now draw the structure with a hexagonal benzene ring, marked by alternating double bonds. At the second carbon position, draw an ethyl group (C2H5). At the first and third positions, draw a methyl group (CH3). This completes the structural formula for 2 -ethyl-1,3-dimethylbenzene.

Key concepts

The Benzene Ring

In organic chemistry, the benzene ring is fundamental to understanding aromatic compounds. This hexagonal ring structure consists of six carbon atoms linked by alternating single and double bonds, which creates a planar ring with equal bond lengths, called resonance. The ring's stability, known as aromaticity, comes from this electron delocalization over the entire ring.

The concept of a benzene ring is vital when drawing structural formulas for aromatic compounds. Each carbon atom in the ring normally has one hydrogen attached, but these can be replaced by other atoms or groups of atoms known as substituents. In the exercise, we replace some of the hydrogens with chlorine atoms and alkyl groups like an ethyl or methyl group.

Substituents in Organic Compounds

Substituents are atoms or groups of atoms that replace hydrogen atoms on the basic skeleton of an organic molecule. They play a crucial role in determining the physical and chemical properties of the compound. When it comes to benzene rings, common substituents are halogens (like chlorine), alkyl groups (such as methyl or ethyl), and other functional groups.

In our exercise examples, dichloro- and dimethyl- are substituents. Their position is crucial and is indicated by numbers in the compound's name, corresponding to the carbon atoms on the benzene ring to which they are attached. The names tell us not only which substituents are present but also their exact locations on the ring, critical for drawing the accurate structure.

Drawing Chemical Structures

Drawing chemical structures accurately is essential in organic chemistry. It provides a visual representation of the molecule, showing how atoms are bonded and the layout of the molecular framework. Start with a clear depiction of the benzene ring, then add substituents at the correct positions as indicated by the compound's name. Alternate between single and double bonds around the ring to preserve the aromatic nature.

Remember to draw straight lines to represent bonds and include all functional groups and substituents. In some cases, you may need to draw the hydrogen atoms, but in other instances, such as with benzene rings, they are often omitted for simplicity, as long as all carbon atoms have four bonds.