Question

Which of the following is not a primary amine:
A.tert-Butylamine
B.sec-Butylamine
C.iso-butylamine
D.dimethylamine

Answer 1

Hint: To answer this question, you should recall the concept of nomenclature of amines. Amines are the chemical species with one or more atoms of nitrogen. A primary amine has ${\text{N}}{{\text{H}}_2}$ group attached to the chain.

Complete step by step answer:
 The nitrogen in ammonia is similar to the nitrogen in amines as nitrogen can bond up to three hydrogens. Although the carbon connected to nitrogen affects its chemical properties. In the case of amines, the carbon atoms bonded to the nitrogen atom are counted. By this way, we can classify amines as primary, secondary, or tertiary according to the number of carbons bonded directly to the nitrogen atom.
The simplest amine i.e. in case of primary amines only one carbon is bonded to the nitrogen atom. In case of secondary amines, two carbon atoms are bonded to the nitrogen atom, and tertiary amines have three carbons bonded to the nitrogen. Dimethylamine \[\left[ {{{{\text{(C}}{{\text{H}}_{\text{3}}}{\text{)}}}_{\text{2}}}{\text{NH}}} \right]\] is a secondary amine as the central Nitrogen atom is substituted by two methyl groups and the nitrogen has one hydrogen.
Tert-butyl amine, secondary butylamine, isobutylamine are all the isomers of n-butyl amine, varying in the position of the N−group in the alkyl chain.

Hence, the correct answer to this question is option D.

Note:
Unlike ammonia, amines act as bases with few of them with strong basicity. In case of resonating amines, the lone pair which is present over nitrogen in the amine group is "drawn in" towards this delocalisation and this interaction makes the lone pair less available to bond to an incoming hydrogen ion. More electrons are available around nitrogen as ethyl is an electron-donating group. Lone pair of electrons on nitrogen is involved in delocalisation. This is the reason that amines are basic.
Nomenclature of amines: Oldest and most typically used alkane series naming system is to classify every cluster connected to the gas atom so add the ending-amine, as in methylamine: \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{N}}{{\text{H}}_{\text{2}}}\] ; N-ethyl-N-propylamine: \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{NHC}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{3}}}\].