If there are two longest chains possible in an organic compound and both have the same number of substituents, how do we decide the parent chain?

Question

Is the parent chain in the above case determined by atomic mass, alphabetical preference or any other rule?

score -1 · Accepted Answer · answered May 03 '15 at 16:42

-1

If two longest chain are possible with same number of side chain in both of them, then we consider sum of locants of the side chain. The longest chain in which the sum of locants of the side chain is least is taken into consideration.

answered May 03 '15 at 16:42

sedflix

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If the sum of the locants is also same, then? – the_random_guy42 May 03 '15 at 16:44
In that case alphabetical order is follwed.. – sedflix May 03 '15 at 16:46
Alphabetical order in what sense? – the_random_guy42 May 03 '15 at 16:48
This is incorrect; we determine the point of first difference of locants between the two possible chains, and prefer the smallest number: https://www.acdlabs.com/iupac/nomenclature/79/r79_933.htm#ID_73zo0o – lirtosiast May 28 '20 at 04:30
This answer is wrong. See also IUPAC nomenclature: "Smallest sum of locants"? – Loong Nov 06 '21 at 09:00

If there are two longest chains possible in an organic compound and both have the same number of substituents, how do we decide the parent chain?

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