I think I numbered it the correct way but I do not know which is the correct way to name it. Also please give the correct reason.

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My answer was:

cyclohexane 1-carboxylic acid 2-oxo 4-carbaldehyde


4-carbaldehyde 2-oxocyclohexane - carboxylic acid


According to the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book), the order of seniority of classes in decreasing order of seniority is as follows.

7. acids
15. aldehydes
16. ketones

Thus, the principal characteristic group of the compound that is given in the question is the carboxylic acid group. This principal characteristic group is expressed at the end of a name by means of a suffix or a class name, i.e. ‘cyclohexanecarboxylic acid’.

The other groups of the given compound cannot be expressed as a suffix. The cyclohexanecarboxylic acid is substituted using the usual principles of substitutive nomenclature.

For the aldehyde group, the suffix ‘carbaldehyde’, which generally can be used when the $\ce{-CHO}$ group is attached to a ring as in cyclohexanecarbaldehyde, cannot be used in this case. Instead, the prefix ‘formyl’ can be used in the presence of a characteristic group having priority to be cited as a suffix or when the $\ce{-CHO}$ group is attached to a side chain.

Likewise, the suffix ‘one’, which generally can be used to form the name of ketones as in cyclohexanone, cannot be used in this case. Instead, the prefix ‘oxo’, denoting $\ce{=O}$, is used to indicate a carbonyl group when the group cannot be cited as suffix.

Therefore, the correct name for the given compound is 4-formyl-2-oxocyclohexane-1-carboxylic acid.

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