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Imagine a molecule that has aldehyde and alkene group, then how do you choose the longest chain to name as parent chain. Does the parent chain have to include both aldehyde and alkene group even if there is a larger one just with an aldehyde group?

My TA says that you choose the parent chain that has both aldehyde and alkene chain, if possible, even if it is the shorter chain, without giving any further reasons for that. So then my question is that is it possible for parent chain to include more than 2 functional groups? Like I know the likelihood of seeing such an example may be rare, but if you have a molecule that includes a chain, among other candidates, with more than 2 functional groups, like a carboxylic acid, alkene, alcohol or aldehyde and so on all in one chain… then can you choose such a chain as a parent chain over any other chain anytime when that other chain has fewer functional groups or is even longer or shorter? If yes, then would you say that when finding the parent chain we should try to find parent chain that not only has the highest priority substituent but also the one that has most high priority substituent as possible?

Also, one more question, let's say you have a parent chain that has ketone at second carbon atom from one side of the linear chain and an alcohol group on carbon 1 when viewed from the other end? Even though ketone has higher substituent than alcohol, where would you start numbering the molecule? Would carbon with aldehyde be numbered 2 and carbon attached to alcohol 6 or 7? Or would carbon with alcohol be 1 and ketone be numbered 5 or 6?

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closed as too broad by hBy2Py, airhuff, Todd Minehardt, M.A.R., Loong Apr 8 '17 at 16:54

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