Question

Give the structure of each of the following aromatic hydrocarbons. a. \(o\) -ethyltoluene b. \(p\) -di-tert-butylbenzene c. \(m\) -diethylbenzene d. \(1-\) phenyl- 2 -butene

Short answer

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Step-by-step solution

Understand IUPAC Nomenclature

The IUPAC naming system for organic compounds is a standardized method for naming organic molecules based on the main carbon chain and the attached functional groups. The prefixes "ortho" (o), "meta" (m), and "para" (p) are used to describe the relative positions of substituents on the benzene ring. Ortho- means the substituents are on adjacent carbon atoms, meta- means they are separated by one carbon atom, and para- means they are opposite to each other. Additionally, numbers may also be used to indicate the positions more explicitly. Now let's draw the structures for each given aromatic hydrocarbon.

Draw the Structure of o-ethyltoluene

First, identify the main structure as a benzene ring. Toluene has a methyl group (CH₃) attached to the benzene ring. In o-ethyltoluene, an ethyl group (CH₂CH₃) is also attached to the benzene ring ortho- to the methyl group (i.e., adjacent to the methyl group). The structure of o-ethyltoluene is: 

Draw the Structure of p-di-tert-butylbenzene

Start with a benzene ring. In this case, two tert-butyl groups (C(CH₃)₃) are positioned para- to each other (i.e., opposite to each other) on the benzene ring. The structure of p-di-tert-butylbenzene is: 

Draw the Structure of m-diethylbenzene

Again, start with a benzene ring. For m-diethylbenzene, there are two ethyl groups (CH₂CH₃) attached to the benzene ring in meta-positions (i.e., separated by one carbon atom). The structure of m-diethylbenzene is: 

Draw the Structure of 1-phenyl-2-butene

In this case, we have a butene molecule (four carbon atoms in a chain with a double bond between the 2nd and 3rd carbons). The 1-phenyl- part indicates that a benzene ring (phenyl group) is attached to the first carbon of the butene chain. The structure of 1-phenyl-2-butene is: 

Key concepts

IUPAC Nomenclature

The IUPAC (International Union of Pure and Applied Chemistry) nomenclature is a system that provides a standardized way of naming organic compounds. This systematic approach makes it easier for chemists to understand the structure of a compound based on its name. In the case of aromatic hydrocarbons, the benzene ring serves as the basic structure, with various substituents attached to it. The position of these substituents is indicated using a combination of prefixes and numbers.

• For example, "ortho" (o-) denotes that two substituents are on adjacent carbon atoms within the benzene ring.
• "Meta" (m-) implies that the substituents are separated by one carbon atom.
• Lastly, "para" (p-) indicates that two groups are on opposite sides of the ring.

When a benzene ring has more than two substituents, numbers are used instead (e.g., 1, 2, 3...) to specify the exact location on the ring. Understanding this nomenclature is crucial for drawing the correct structure and conceptualizing how the molecule may interact in chemical reactions.

Structural Formula

The structural formula of a molecule represents the arrangement of atoms within that molecule. It goes beyond a simple molecular formula by showing how atoms are connected to each other. In aromatic hydrocarbons, this is particularly important due to the delocalized electrons in the benzene ring that form a stable structure.
For example, when drawing the structural formula of an aromatic hydrocarbon like o-ethyltoluene, you first start with the benzene ring as the base structure. Then, identify the specific groups, such as a methyl group (CH₃) for toluene and an ethyl group (CH₂CH₃), and place them on the appropriate carbon atoms according to the given positions.

• The structural formula helps in visualizing the spatial arrangement of the molecule, providing insights into its properties and potential reactions.
• While sketching the structural representation, ensure that all carbon and hydrogen atoms are correctly represented, respecting the rules of chemistry like tetravalency of carbon.

Substituents Positions

In aromatic hydrocarbons, substituents can be positioned in different locations around the benzene ring. These positions are crucial for determining the compound's chemical properties and are defined using the terms ortho, meta, and para. Being aware of the positions can significantly affect the molecular interactions and reactivity.

• Ortho-position: Substituents are located on adjacent carbon atoms.
• Meta-position: Substituents are separated by a single carbon atom.
• Para-position: Substituents are on opposite sides of the benzene ring.

When identifying the correct positions, it's also useful to employ numbering systems, especially when dealing with complex structures. Proper identification of these positions ensures accuracy in experimental setups and theoretical predictions.