Monday, 25 July 2016

organic chemistry - Nomenclature of alkoxy and halo groups



CH3-O-CH2CH2Cl


How will this compound be named? Both, methoxy and chloro are given equal preference, since they are prefix functional groups. The answer given in the book is 2-chloro-1-methoxyethane, but why is it not 1-chloro-2-methoxyethane, as the C of chlorine comes before M in the alphabetical order?



Answer




Your name, 1-chloro-2-methoxyethane, is correct.



Here is a link to the relevant page of the 1993 edition of the IUPAC Blue Book - Nomenclature of Organic Chemistry, which is published online by ACD Labs with permission of IUPAC.


Here are some example ethers and sulfides from that page, and we see a similar case to yours:


example IUPAC ether nomenclature


There is no difference in preference or priority between halo and alkoxy substituents (or any of the other prefix only substituents). Thus, in a case where there are two such groups and assignment of locants generates the same combination either way, you choose to assign the lower locant number to the alphabetically first.



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