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I thought that the correct IUPAC name for the molecule below (benzyl chloride) would be chloromethylbenzene because the ring always gets priority over the chain unless a primary functional group is present. However, it seems the correct name is chlorophenylmethane. Can someone explain why that is?

chloromethylbenzene or chlorophenylmethane?

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The preferred IUPAC name is, indeed, (chloromethyl)benzene, built from substitutive prefix chloromethyl. The parentheses around "chloromethyl" are required because it is a compound substituent (a simple substituent attached to another simple substituent, specifically, methyl and chloro in this case). The Blue Book [1, p. 66] has plenty of examples similar to yours:

$$ \begin{array}{lll} \ce{C6H5-CH2-NCS} &\quad &\text{benzyl isothiocyanate} \\ & &\text{(isothiocyanatomethyl)benzene (PIN)} \\ & & \\ \ce{C6H5-NC} &\quad &\text{phenyl isocyanide} \\ & &\text{isocyanobenzene (PIN)} \end{array} $$

Note that common names for this molecule also include: benzyl chloride and α-chlorotoluene.

References

  1. Favre, H. A.; Powell, W. H. IUPAC “Blue Book” Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names; IUPAC Recommendations; Royal Society of Chemistry: Cambridge, England, 2013. ISBN 978-0-85404-182-4.
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    $\begingroup$ The remark about the use of parentheses is correct. However, the actual question was whether the preferred name is chloro(phenyl)methane or (chloromethyl)benzene. $\endgroup$ – Loong Jun 29 at 12:00
  • $\begingroup$ @Loong You are right. I was (and still am) too lazy to look up the relevant rules so just decided to edit in a brief line about the parentheses; I leave it to you if you want to expand further or write another answer. $\endgroup$ – orthocresol Jun 29 at 13:02
  • $\begingroup$ Is 1-phenyl methyl chloride possible? $\endgroup$ – Chakravarthy Kalyan Jun 30 at 2:43

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