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How to select the parent carbon chain for IUPAC naming of following compound?

2-bromo-3,6-diethylnonan-5-ol

I think the red numbering is correct, but in the answer key, they have used the blue numbering.

Which is correct?

My question is regarding selection of parent chain in an alcohol. While selecting the parent carbon chain (base name) to write the IUPAC name of an alcohol, do we have to give preference to the one which gives the lowest locant to the $\ce{–OH}$ group (viz. primary functional group here), or the one which has the maximum number of carbon atoms?

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  • $\begingroup$ MarvinSketch program gives 2-bromo-3,6-diethylnonan-5-ol $\endgroup$
    – Maurice
    Oct 26 '20 at 10:56
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When assigning numbers to carbon atoms in an aliphatic skeleton, your first priority must be the longest carbon chain. The chain with red numbers is one carbon atom smaller than the one with blue numbers. Blue - 9, red - 8. It's also helpful to know that when you have two carbon chains of the same length, the one that's the most branched must be assigned the highest priority. Here we have exactly this case, where two chains of the same length can be found. One of them has 4 branches (2 ethyl radicals, 1 alcohol and 1 bromide) and the other one has 3 branches (1 hydroxyl, 1 ethyl and 1-(1-bromoethyl)).

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