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Sorry if this question was answered before, but I could not find a satisfactory answer from related questions. enter image description here

Anyways, I have trouble identifying the main carbon chain in above structure. As you can see, there is a carboxylic substituent connected to the longest carbon chain which has 7 carbon atoms. So when numbering the chain the active functional group should receive the smallest number according to IUPAC rules. So, if we begin from the carbon atom in the carboxylic substituent , there will be 6 atoms in the carbon chain but, the main functional group will receive the smallest number. Or, should I choose the longest chain possible despite above facts.

Also , I am quite unclear which number does the carboxylic group get if we choose the longest chain?

Could anyone answer the above 2 questions please...

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    $\begingroup$ Does this answer your question? When we name an organic compound ,if there is double bond and a functional group which is now a substituent who has priority? $\endgroup$
    – Nisarg Bhavsar
    Commented Aug 22, 2021 at 10:51
  • $\begingroup$ @NisargBhavsar no, actually my question is ,do we consider giving the carbon atom of main functional group the lowest number possible.....despite it is not the longest chain? $\endgroup$
    – donthababakka
    Commented Aug 22, 2021 at 11:12
  • $\begingroup$ Did you read the answer to the linked question fully? The first rule clearly states that the primary functional group is given priority over chain length. $\endgroup$
    – Nisarg Bhavsar
    Commented Aug 22, 2021 at 11:14
  • $\begingroup$ I am adding an answer to make my point clearer. $\endgroup$
    – Nisarg Bhavsar
    Commented Aug 22, 2021 at 11:27
  • $\begingroup$ The details in this anser gives the recent IUPAC recomondations of how to choose the principle chain. $\endgroup$
    – Mathew Mahindaratne
    Commented Aug 22, 2021 at 11:43

1 Answer 1

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The following are the rules given by Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013[1] for selecting the primary/parent carbon chain/skeleton:

P-44.1 SENIORITY ORDER FOR PARENT STRUCTURES

When there is a choice, the senior parent structure is chosen by applying the following criteria, in order, until a decision is reached. These criteria must always be applied before those applicable to rings and ring systems (see P-44.2) and to chains (see P-44.3). Then criteria applicable to both chains and rings or ring systems given in P-44.4 are considered.

P-44.1.1 The senior parent structure has the maximum number of substituents corresponding to the principal characteristic group (suffix) or senior parent hydride in accord with the seniority of classes (P-41) and the seniority of suffixes (P-43).

(…)

P-44.3.2 The principal chain has the greater number of skeletal atoms [criterion (b) in P-44.3].

(…)

It is clear from the first two rules itself that the primary functional group is given priority over the length of the parent chain and thus in your example the carboxylic acid should be given priority over the possible longer parent chain.

Thus the preferred IUPAC name of your example will be 2-ethylhexanoicacid.

Reference:

(1) Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013; Royal Society of Chemistry: Cambridge, 2013.

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