Difference WikiChemistry

Difference Between Primary Amines, Secondary Amines and Tertiary Amines

Main Difference

The main difference between Primary Amines, Secondary Amines, and Tertiary Amines is that Primary Amines have one alkyl or aryl group attached to the nitrogen atom in their structure, whereas Secondary Amines have two alkyl or aryl groups attached to the nitrogen atom in their structure, and Tertiary Amines have three alkyl or aryl groups attached to the nitrogen atom in their structure.

Primary Amines vs. Secondary Amines vs. Tertiary Amines

The structure of primary amines comprises of one alkyl group bonded to each nitrogen atom; the structure of secondary amines comprises of two alkyl groups bonded to each nitrogen atom leaving one hydrogen atom bonded with the nitrogen atom. However, for tertiary amines, the structure comprises three alkyl groups bonded to each nitrogen atom, thus leaving no hydrogen atom bonded to a nitrogen atom.

ADVERTISEMENT

Primary amines are less basic than both secondary and tertiary amines but more basic than ammonia; secondary amines are found more basic than all amines, including primary, tertiary amines, and ammonia, whereas, tertiary amines are found less basic than secondary amines but more basic than primary amines and ammonia.

In primary amines, no considerable steric hindrance is found; for secondary amines, considerable steric adherence is also not found, but tertiary amines show steric hindrance due to the attached alkyl groups on the same nitrogen atom. While naming primary amines their alkyls or aryl groups are mentioned as a prefix; while naming secondary amines the two alkyl or aryl groups attached are needed to be mentioned in their name, however, while pronouncing tertiary amines all of the three alkyl or aryl groups attached are needed to be mentioned in their name.

ADVERTISEMENT

Comparison Chart

Primary AminesSecondary AminesTertiary Amines
Amines that have one alkyl or aryl groups are called primary amines.Amines that have two alkyl or aryl groups attached to the nitrogen atom in their structure are called secondary amines.Amines that have three alkyl or aryl groups attached to the nitrogen atom in their structure are called tertiary amines.
Structure
One alkyl or aryl group is attached to the nitrogen atom in their structure.Two alkyl or aryl groups are attached to the nitrogen atom in their structure.Three alkyl or aryl groups are attached to the nitrogen atom in their structure.
Basicity
They are less basic than both secondary and tertiary amines but more basic than ammonia.They are more basic than all amines, including primary, tertiary amines, and ammonia.Tertiary amines are less basic than secondary amines but more basic than primary amines and ammonia.
Steric Hindrance
No great steric hindrance.No large steric interruption.They show steric hindrance due to the attached alkyl groups on the same nitrogen atom.
Nomenclature
Their alkyls or aryl groups are mentioned as a prefix.The two alkyl or aryl groups attached are needed to be mentioned in their name.The three alkyl or aryl groups attached are needed to be mentioned in their name.
ADVERTISEMENT

What are Primary Amines?

Primary amines are the amines that contain only one alkyl, or aryl group that is attached to the nitrogen atom in their structure as an ammonia molecule is bonded to three hydrogen atoms, one of these hydrogen atoms un-bonds with the nitrogen atom and gets replaced by an alkyl or an aryl group. An alkyl group is a functional group that is found in organic molecules.

Its structure can be explained as, as a hydrogen atom loses bond in this group, a vacant point is formed. This vacant place can be filled by another atom. In the case of primary amine, this vacant space gets filled by attaching itself to a nitrogen atom of the ammonia group, which leads to the formation of primary amines. In the case of Aryls, an aryl group always contains a ring.

Aryl group is categorized as simple aromatic compounds where one hydrogen atoms are removed from its group and leaving the position vacant for attachment with another atom. This vacant space is filled in this case with the ammonia group leading to the formation of primary amines.

While naming primary amines, their alkyls or aryl groups are mentioned as a prefix. As if a methyl group is present in primary amine. The compound is named as methylamine. But, if amine contains more functional groups in their structure, their substituent name is given to them. As for the amine group, the substituent name is “amino.”

Amines act as bases with litmus test due to the presence of lone pairs in one of their nitrogen atoms that are donated to protons. The process occurs when amine reacts with water; they form OH ions by donating their lone pair to hydrogen atom of H2O. As bases are the compounds that release OH ions, amines act as bases by following the same path.

The basicity of amines is observed by checking the stability of the compound formed after the donation of lone pairs. When the lone pair is donated by primary amines, the nitrogen atoms gets a positive charge. The positive charge is reduced while withdrawing the electrons towards them. Since there is only one alkyl group in primary amines, they act less basic than secondary amines.

What are Secondary Amines?

Secondary amines are the amines that contain two alkyls or aryl group that is attached to the nitrogen atom in their structure. As two of the hydrogen atoms un-bonds with the nitrogen atom (as ammonia molecule is bonded to three hydrogen atoms) and gets replaced by alkyl or aryl groups, which leads to the formation of secondary amines.

In the case of Aryls, an aryl group always contains a ring. Aryl groups are categorized as simple aromatic compounds where two hydrogen atoms are removed from its group and leaving the position vacant for attachment with other atoms. The vacant spaces are filled in this case with ammonia groups leading to the formation of secondary amines.

The nomenclature of secondary amines differs as the two alkyl or aryl groups attached are needed to be mentioned in their name. As, N- ethyl -N- propyl amine stands for a secondary amine consisting of a nitrogen atom bonded to a hydrogen atom, an ethyl group, and a propyl group.

Secondary amines also act as basic but more basic than primary and tertiary amines. The basicity of amines is observed by checking the stability of compound formed after the donation of lone pairs and their acceptance of protons. The alkyl groups are electron-donating. The nitrogen atom is reduced by electron-donating property of alkyls as they reduce nitrogen atoms. Hence, these secondary amine performs more basic as compared to other amine forms.

What are Tertiary Amines?

Tertiary amines are the amines that contain three alkyls or aryl groups attached to a nitrogen atom in their structure. These amines are formed by the replacement of all three hydrogen atoms. Because they contain three hydrogen atoms bonded with the nitrogen atom, these are replaced by alkyl or aryl groups, thus leading to the formation of secondary amines. Therefore, no hydrogen atom remains in the structure of ammonia.

In the case of Aryls, an aryl group always contains a ring. The vacant spaces in aryls filled in this case with the ammonia group leading to the formation of tertiary amines. Nomenclature of tertiary amines differs as the three alkyl or aryl groups attached are needed to be mentioned in their name. For example, in the case of tributylamine, the nitrogen atoms are bonded to three butyl groups, which can be represented as (CH3CH2CH2CH2) 3N.

Tertiary amines act as basic but more basic than primary amines and ammonia but less basic than secondary amines; this is due to steric adherence as the three alkyl groups attached to one nitrogen atom. The alkyl groups are electron-donating. The nitrogen atom is reduced by electron-donating property of alkyls as they reduce nitrogen atoms.

Key Differences

  1. Primary amines have one alkyl or aryl group attached to the nitrogen atom; secondary amines have two alkyl or aryl groups attached, but tertiary amines have three alkyl or aryl groups attached to a nitrogen atom.
  2. The primary amines consist of one alkyl group attached to each nitrogen atom; secondary amines consist of two alkyl groups bonded to each nitrogen atom; however, tertiary amines consist of a structure of three alkyl groups bonded to each nitrogen atom and are different from both primary and secondary amines.
  3. Primary amines are less basic than both secondary and tertiary amines; secondary amines are found more basic than all amines, whereas, tertiary amines are found more basic than primary amines and ammonia but less basic than secondary amines.
  4. In primary amines, there is no considerable steric hindrance; secondary amines are a considerably steric hindrance, but tertiary amines show considerable steric hindrance.

Conclusion

Primary amines consist of one alkyl or aryl group, while secondary amines have two alkyl or aryl groups, whereas, the tertiary amines are bonded with three alkyl or aryl groups. These are all attached to the nitrogen atom with their structure.

Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss