amines and amides Flashcards
what is the homologous series of amines
NH2 this is an amine functional group
how can we prepare an amine
by reacting a halogenalkane with ethanoic ammonia (NH3)
This reaction requires:
- excess ammonia
- high pressure
- heat
this is a nucleophillic substitution
how do we make an amide
by reacting a primary amine with acyl chloride/ acid anhydride or with ammonia
the reaction with ammonia produces a carboxylic acid while the creation with the primary amide produces a N-substituted amide
what are the different classifications of amines
primary
secondary
tertiary
we classify amines according to the number of carbons bonded directly to the nitrogen
what are aliphatic and aromatic amines
if a benzene is directly bonded to nitrogen then it is an aromatic
when there isn’t a benzene ring directly bonded then it is an aliphatic amine. A lot of these compounds are found in oil
the base properties of amines
when amines react wuth H2S they react like this:
R-NH2 + H2S = R-NH3+ +HS
amines form a bond with H from H2S. The amine therefore acts as a base. Not all amines are equal in base strength
how do we measure base strength
using a universal indicator for example
how do we determine base strength
The more available a lone pair is, the more likely it is to form a bond and so the stronger the base
The alkyl groups increases the availability of the lone pair to ammonia. This is because the alkyl groups donate electron density to nitrogen this make nitrogen better accepting a proton
This increases the availability of the lone pair making an aliphatic amine a better base than ammonia
why are aromatic amines weaker bases
In benzene, there are 6 p orbitals that overlap forming a pi system
The electrons in the p orbital delocalise
The lone pair of electrons on Nittrogen becomes part of the pi system in benzene
The electrons therefore become delocalised. Therefore, phenyl amine’s lone pairs are less available to react than ammonia’s lone pair so it is a weaker base
what are the properties of amines and amides
the strongest intermolecular force is hydrogen bonding however, tertiary amines and amides do not have nitrogen hydrogen bonds and so no hydrogen bonding
Therefore, primary amines/ amides have a higher melting and boiling point than tertiary amines and amides
tertiary amines and amides can form hydrogen bonds with water and therefore all small amines and amides are soluble in water
what happens to the solubility of molecules as the size increases
as the size of the molecule increases their solubility decreases
This is because a greater region of the molecule is non polar and non polar molecules are highly insoluble in water
why can amines act as bases and nucleophiles
nitrogen has 5 electrons in its outer shell therefore there is a lone pair and so can act as a nucleophile and if the lone pair forms a bond with hydrogen they can also act as bases
describe the base strength of amines
As the number of alkyl groups bonded to nitrogen increases, the strength of the base increases
As the number of benzene rings directly bonded to nitrogen increases the strength of the base decreases
what are quatunary ammonium salts
when the positive ions of amines react with anions it is called a quatenary ammonium salt
these can be used as catatonic sulfactant
what are surfactants
when these dissolve in water., they move to the surface, this is why they are called surfactants
at the surface, the polar end gets surrounded by water molecules - the polar ends are highly soluble in water
The non polar ends poke out from the surface
