(R)2-N-H vs. R-NH2

[StarlingForce1]

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Hi all,

Quick question about amines. Obviously a tertiary amine has very low boiling point because it cannot hydrogen bond, but what is the relationship between primary and secondary amines, with regards to BP? We all know that molecular weight increase corresponds to an increase in BP, but what about the hydrogen bonding? Would methylamine have a higher or lower boilingpoint than N,N-dimethylamine?

Thank you!

🙂

 

[TieuBachHo]

Hi all,

Quick question about amines. Obviously a tertiary amine has very low boiling point because it cannot hydrogen bond, but what is the relationship between primary and secondary amines, with regards to BP? We all know that molecular weight increase corresponds to an increase in BP, but what about the hydrogen bonding? Would methylamine have a higher or lower boilingpoint than N,N-dimethylamine?

Thank you!

🙂

With respect to compounds of similar molecular structures, the hydrogen bonding takes precedence. The primary amine has 1 more hydrogen bonding than the secondary amine and thus it has a higher bp.

 

[StarlingForce1]

With respect to compounds of similar molecular structures, the hydrogen bonding takes precedence. The primary amine has 1 more hydrogen bonding than the secondary amine and thus it has a higher bp.

Hi Tieu,

Thank you, but does this mean that H-bonding overrides molecular weight then?

For instamce, N,N-dipropylamine is substantively heavier than Propylamine, but propylamine would have 1 more h-bond than N,N-dipropylamine....

 

[gettheleadout]

Hi Tieu,

Thank you, but does this mean that H-bonding overrides molecular weight then?

For instamce, N,N-dipropylamine is substantively heavier than Propylamine, but propylamine would have 1 more h-bond than N,N-dipropylamine....

This is one of those things where there won't be a hard-and-fast rule, it will depend on the compounds considered.