Amines Flashcards
Differences between primary, secondary and tertiary amines
Primary: 1 carbon chain attached to nitrogen
Secondary: 2 carbon chains attached to nitrogen
Tertiary: 3 carbon chains attached to nitrogen
Differences in boiling points of primary, tertiary and secondary amines
Primary amines have higher boiling points as they can form hydrogen bonds with each other as well as van der Waals’ and permanent dipole-dipole interactions.
Secondary amines can also form hydrogen bonds but with the amine in the middle of the chain, the permanent dipole is less.
Tertiary amines cannot form hydrogen bonds with each other as there are no hydrogen atoms attached directly to the nitrogen.
Solubility of amines
All of the amines can form hydrogen bonds with water - even the tertiary ones.
Although the tertiary amines don’t have a hydrogen atom attached to the nitrogen and so can’t form hydrogen bonds with themselves, they can form hydrogen bonds with water molecules just using the lone pair on the nitrogen.
Smell of amines
As the amines get bigger, they tend to smell more “fishy”
How do amines act as bases?
The lone pair of electrons on the nitrogen atoms can accept a proton (and form a dative covalent bond)
Amine reactions with acids
The NH2 group gains an H+ leading to NH3+ attached to negatively chrged ion, forming a salt
Reaction of amines with water
React like ammonia, an H+ is taken from water forming an NH3+ ion and an OH- ion
Comparison of strengths as a base of alkylamines, ammonia and primary arylamines
(Stretch and challenge)
Alkylamines tend to be stronger bases than ammonia because the alkyl groups are more electron donating than H atoms so there is a higher electron density around the N atoms and the lone pair of electrons. Thus, a stronger bond is formed with an H+ ion. Primary arylamines are weaker bases than ammonia or alkylamines as the lone pair becomes partly delocalised into the benzene ring and is less available to bond to an H+ ion.
What is one possible problem with the synthesis of alkyl amines and how can it be reduced?
The product has a lone pair of electrons and can react with the halogenoalkane to form hydrogen halide + organic mixture (look at p.38) can be reduced through increasing the pressure/conc. of ammonia.
What is an amino acid?
A compound containing an -NH2 group and a carboxylic acid group
What is an alpha amino acid?
An amino acid with the amino group attached to the carbon atom adjacent to the -COOH groups
What is the general formula of an alpha amino acid?
RCH(NH2)COOH
What is a zwitterion?
A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. Both charges are present so there is no overall charge.
What the the isoelectric point?
The pH value at which the amino acid exists as a zwitterion
How does R group affect isoelectric point? ***
If you add basic groups such as NH2 to the R side chain, there’s a greater chance of protonation at any given pH as there are now two proton acceptors in the amino acid. As a result, the pH needs to be higher to prevent any charges arising from protonation, hence the isoelectric point is higher.
If you add acidic groups such as COOH to the R side chain, there’s a greater chance of deprotonation at any given pH as there are now two proton donators in the amino acid. As a result, the pH needs to be lower to prevent any charges arising from deprotonation, hence the isoelectric point is lower.
Amino acid in an environment more acidic than isoelectric point
Amino acid behaves as a base and accepts a proton from the acid, forming a positively charged ion
Amino acid as an acid (in more basic environment than isoelectric point)
Amino acid donates a proton to the base forming a negatively charged ion and water
Reaction of alanine (CH3CH(NH2)COOH) with HCl
Cl- + CH3CH(NH3+)COOH formed
Reaction of glycine (CH2(NH2)COOH) and NaOH
Forms H2O + CH2(NH2)COO-Na+
What feature of amino acids allows them to form polymers?
The contain both amine and carboxyl groups so can form peptide links
What is condensation?
A reaction in which two small molecules react together to form a larger molecule with the elimination of a small molecule such as water
What does condensation polymerisation require?
Monomers with two different functional groups
What is a polyester and what groups do the monomers contain?
A polyester is formed when monomer units which contain a carboxyl and hydroxyl group are bonded together through ester linkages
General formula for forming a polyester with one type of monomer
n HO - A - COOH (hydroxycarboxylic acid) -> -[-O-B-CO-]- n + H2O
