Question

Which group is always taken as a substituent in the IUPAC system of nomenclature?
(A)$ - N{O_2}$
(B)

(C)

(D) $ - N{H_2}$

Answer 1

Hint:In the IUPAC system there is an order of priority of the functional groups according to which the naming of a compound is done. We need to check that order to decide which group will act as a main functional group and which group will be named as a substituent group.

Complete step by step answer:
According to the IUPAC, the group which comes first in the priority order will be treated as the main group in the chain and the rest other groups that are present in the chain will be treated as a substituent group.
The priority order of the functional group is:
\[COOH > S{O_3}H > COOR > COX > CON{H_2} > CN > NC > CHO > C = O > {{OH}} > N{H_2} > OR\]
The groups which are present in this list are called principal functional groups. The rest of the groups are called subordinate functional groups which are cited as prefixes most of the time.
Now, from the above list, we can deduce that out of the given options that we have only $ - N{O_2}$ group is not present in the list.
Therefore, $ - N{O_2}$ group will be treated as a substituent group in the main chain, and its naming will be done as a prefix in the organic compound.

Hence, Option (A) is correct.

Note:
Those organic compounds which contain $ - N{O_2}$ as the functional group are known as nitro compounds. These compounds could be aliphatic or aromatic depending as the nitro group is attached to an alkyl group or an aryl group. These are classified into three categories;
(a) Primary Nitroalkane: $ - N{O_2}$ is attached to the Primary C-atom.
(b) Secondary Nitroalkane: $ - N{O_2}$ is attached to the secondary C-atom
(c) Tertiary Nitroalkane: $ - N{O_2}$ is attached to the tertiary C-atom.