How to name aliphatic chain with carboxyl and amide terminal groups?

Question

I know the name 5-carboxyl-2-methylethanoic acid is wrong for the compound $\ce{HOOC-CH(CH3)-CH2-CH2-CH(CH3)-C(=O)-NH2}$ drawn below. Can we just use 5-amido?

Answer 1

No, amido will not work here. According to IUPAC 2013,

P-35.3 COMPOUND SUBSTITUENT PREFIXES

P-35.3.1 Names of compound prefixes derived from suffixes or functional parent compounds may be formed by substituting simple prefixes into other simple prefixes. When there is a choice, P-57.4 provides for the selection of a preferred compound prefix.
Examples:
–SSeH selanylsulfanyl (preselected prefix)
–NH-Cl chloroamino (preselected prefix)
–NH-CH3 methylamino (preferred prefix)
–PH-Cl chlorophosphanyl (preselected prefix)

As we have a -CO-NH$_2$ on the 5th carbon (numbered from left to right (as carboxylic acid has higher priority)), it will be named aminocarbonyl because it is a carbonyl group (=O) attached to an amino group (-NH$_2$)

Therefore a systematic IUPAC name can be 5-aminocarbonyl-2,5-dimethylhexanoic acid.

Note that this is a systematic name and might not be the compound's Preffered IUPAC Name (PIN).

Answer 2

You have correctly identified the principal characteristic group as acid, which is expressed as suffix. The amide can be expressed as various prefixes.

The corresponding subsection in the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) reads as follows:

P-66.1.1.4.1.1 In presence of a characteristic group having priority for citation as suffix or if all carbamoyl groups cannot be included in the suffix, the $\ce{-CO-NH2}$ group is named in three different ways:

1. by using the two prefixes ‘amino’ and ‘oxo’ to denote such groups on terminal atoms of carbon chains having more than one carbon atom;
2. by using the acyl group name ‘carbamoyl’ (see P-65.2.1.5);
3. by using the prefix ‘aminocarbonyl’.

For generation of IUPAC preferred names, method (1) is preferred for chains and method (2) for rings and ring systems, heterogeneous chains, and on nonterminal atoms of carbon chains. Carbamoyl and amino groups may be substituted in the normal way.

The corresponding names for the compound that is given in the question are:

1. 6-amino-2,5-dimethyl-6-oxohexanoic acid (PIN)
2. 5-carbamoyl-2-methylhexanoic acid
3. 5-aminocarbonyl-2-methylhexanoic acid