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

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SUMMARY

The correct nomenclature for the compound in question is pentan-2-yl benzene, as per IUPAC guidelines. The designation "2" indicates that the phenyl group is attached to the second carbon of the pentane chain. This specificity is crucial to avoid ambiguity regarding the attachment point of the benzene ring, which can occur at multiple positions on the pentane chain. The discussion highlights the importance of precise naming conventions in organic chemistry to ensure clarity in compound identification.

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Sunwoo Bae
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TL;DR
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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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).
 

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