Naming the pentane with phenyl group (or benzene with aryl group)

In summary, the name for this compound, 2-pentylbenzene, indicates that there is a phenyl group in the second carbon of pentane. However, this name is not ideal as it is ambiguous and can be misinterpreted as the position relative to either the pentane or the benzene ring. According to IUPAC, the correct name should be pentan-2-yl benzene, following the same naming convention as cumene (or isopropylbenzene). The 2 in the name is necessary because the benzene can attach to the pentane chain at different positions.
  • #1
Sunwoo Bae
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TL;DR Summary
My textbook indicates that the following figure can be named in two ways, but I do not understand how the second one is a valid name.
1612370300975.png


I understand the first one, which indicates that there is a phenyl group in the second carbon of pentane.
But where did the 2 in 2-pentylbenzene come from?
Shouldn't if it be just pentylbenzene, since there is only one subtitute(pentane) on the benzene?
If not, would you explain why?

Thank you.
 
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  • #2
Neither is a great name for this compound. It's ambiguous (or rather would become ambiguous with more substituents) whether the 2 refers to the position relative to the pentane or relative to the benzene ring. IUPAC-wise, it should be pentan-2-yl benzene (cf. cumene, aka isopropylbenzene, as propan-2-yl benzene in the IUPAC scheme). The 2 is necessary because the benzene can attach to the pentane chain at the 1, 2, or 3 position (on the pentane).
 

Related to Naming the pentane with phenyl group (or benzene with aryl group)

1. How do you name a pentane with a phenyl group?

The name of a pentane with a phenyl group is determined by first identifying the longest carbon chain that contains the phenyl group. This chain will serve as the main chain and the prefix "phenyl" is added before the parent chain name. The position of the phenyl group is then indicated by a number before the parent chain name. For example, if the phenyl group is attached to the second carbon in the main chain, the name would be 2-phenylpentane.

2. What is an aryl group?

An aryl group is a functional group that consists of a benzene ring or any other ring structure that is derived from benzene. It is a hydrocarbon group that contains six carbon atoms arranged in a ring with alternating single and double bonds. Aryl groups are often used in organic chemistry to modify the properties of molecules.

3. How do you name benzene with an aryl group?

The naming of benzene with an aryl group follows the same rules as naming a pentane with a phenyl group. The longest carbon chain that contains the benzene ring is identified as the main chain and the prefix "aryl" is added before the parent chain name. The position of the aryl group is then indicated by a number before the parent chain name. For example, if the aryl group is attached to the third carbon in the main chain, the name would be 3-arylbenzene.

4. Can an aryl group be attached to any carbon in a molecule?

Yes, an aryl group can be attached to any carbon in a molecule as long as it is part of a ring structure derived from benzene. This means that the carbon must have three single bonds and one double bond, forming a total of four bonds. This allows the aryl group to be attached to the carbon without disrupting the stability of the molecule.

5. What is the purpose of using aryl groups in organic chemistry?

Aryl groups are often used in organic chemistry to modify the properties of molecules. They can increase the stability of a molecule, alter its reactivity, and change its physical properties such as solubility and melting point. They are also commonly used as functional groups in the synthesis of complex organic compounds.

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