Question

Draw the structure for each compound. \begin{equation}\begin{array}{l}{\text { a. ethylbenzene }} \\ {\text { b. } 1 \text { -iodo- } 2 \text { -methylbenzene }} \\ {\text { c. para- diethylbenzene }}\end{array}\end{equation}

Short answer

a. Ethylbenzene has a benzene ring with an ethyl group attached to it. b. 1-iodo-2-methylbenzene has a benzene ring with an iodine atom on the first carbon and a methyl group on the second carbon. c. Para-diethylbenzene has a benzene ring with ethyl groups on the first and fourth carbons, directly across from each other.

Step-by-step solution

Draw the structure of ethylbenzene

To draw ethylbenzene, start by sketching the benzene ring, which is a hexagon with alternating double and single bonds. Then, add an ethyl group (-CH2-CH3) to any carbon in the benzene ring.

Draw the structure of 1-iodo-2-methylbenzene

Begin again with the benzene ring. Then add a methyl group (-CH3) to the first carbon in the ring. Finally, attach an iodine atom (I) to the second carbon in the ring.

Draw the structure of para-diethylbenzene

Draw the benzene ring one more time. 'Para' signifies that the substituents are attached to carbon atoms on the ring that are opposite each other. Attach an ethyl group (-CH2-CH3) to both the first and fourth carbon atoms on the ring.

Key concepts

Benzene Ring Structure

Understanding the benzene ring structure is fundamental in organic chemistry. Benzene, C6H6, is composed of a ring of six carbon atoms, with alternating double and single bonds, known as aromaticity. This hexagonal structure is exceptionally stable due to the delocalization of electrons above and below the plane of the ring, which is represented by a circle inside the hexagon in many drawings.

• The benzene ring serves as a parent hydrocarbon for numerous compounds in organic chemistry.
• When drawing benzene as part of complex structures, the vertices of the hexagon represent carbon atoms.
• Each carbon atom has one hydrogen attached to it, unless it's connected to a substituent.

In ethylbenzene, the presence of an ethyl group does not disrupt the stability of the aromatic ring, showcasing the versatility of benzene as a backbone for various organic molecules.

Substituent Group Placement

In organic chemistry, it is crucial to accurately represent the placement of substituent groups on a benzene ring. Substituents are groups of atoms that replace one or more hydrogens on a base molecule, which in this case is benzene.

When drawing substituents:

• Identify the carbon atom on the benzene ring to which the substituent will be attached.
• Number the ring's carbon atoms to position the substituents correctly, respecting the IUPAC naming rules.
• In di-substituted benzene compounds, positioning can be indicated by numbered locants (e.g., 1-iodo-2-methylbenzene) or by terms like 'ortho', 'meta', and 'para' for specific relative positions.

For instance, 1-iodo-2-methylbenzene tells us that an iodine atom is attached to the first carbon in the ring, and a methyl group to the second. Meanwhile, in para-diethylbenzene, the term 'para' indicates the ethyl groups are on opposite sides of the benzene ring.

Organic Compound Nomenclature

The nomenclature of organic compounds allows chemists to describe complex molecules in a systematic and universally accepted manner. This structured language includes the naming of various groups attached to the central molecule, such as a benzene ring, and conveys crucial information about the molecule's structure.

• The name of the compound often begins with the name of the substituent groups in alphabetical order, followed by the base molecule.
• Prefixes like 'di-', 'tri-', 'tetra-', and so on, are used to indicate the number of identical substituent groups.
• The position of the substituent groups on the ring is specified using numbers or descriptors like 'ortho', 'meta', and 'para', which refer to 1,2-, 1,3-, and 1,4- positions respectively.

For example, in para-diethylbenzene, 'diethyl' tells us there are two ethyl groups attached, and 'para' indicates their position on the benzene ring.

IUPAC Naming System

The International Union of Pure and Applied Chemistry (IUPAC) naming system is a standard method for naming organic compounds. It provides a unique name to every compound based on its structure to avoid ambiguities. Key elements of the IUPAC naming system include:

• Determining the longest continuous carbon chain or the parent compound, which in the case of benzene derivatives, is 'benzene'.
• Adding prefixes for side chains and substituents in alphabetical order while assigning the lowest possible number to each substituent group.
• When multiple substituents are present, the carbon atoms of the benzene ring are numbered to minimize the numerical locants of the substituents.

Following these rules ensures clarity when conveying the molecular structure of compounds. In 1-iodo-2-methylbenzene, for example, the IUPAC name indicates the positions and types of the substituent groups on the benzene ring.