AMINES Flashcards
(32 cards)
What are amines? (1)
are derivatives of ammonia in which one or more of the hydrogen atoms in the ammonia molecule have been replaced by alkyl or aryl groups
what does the reactivity of amines allow it to do? (1)
amines are very reactive compounds, so they are useful intermediates in synthesis
What do the terms, primary, secondary and tertitary mean in terms of amines? (1)
refer to the number of substituents (R-groups) on the nitrogen atom
what is the formula for amines? (1)
RNH2 where the R can be an alkyl or aryl group.
what is the general formula for secondary amines? (1)
RR’NH
what is the general formula for tertiary amines? (1)
RR’R”N
what are he important properties of amines? (3)
-shape
-boiling points
-solubility
describe the shape of amines. (1)
ammonia is a pyramidal molecule with bond angles of 107 degrees, the difference between this and a normal tetrahedron is caused by the lone pair which repels more than the bonding pairs of electrons in the N-bonds.
describe the boiling points of amines. (1)
primary amines can hydrogen bond to one another using their -NH2- groups, but because nitrogen is less electronegative than oxygen it is not as strong as those found in alcohols. shorter chains are gases at room temperature and those with longer chains are volatile and liquids. they have fish smells.
describe the solubility of amines. (1)
primary amines with short chains are very soluble in water and alcohols because they form hydrogen bonds with these solvents. most amines are soluble in less polar solvents
describe the reactivity of amines. (1)
amines have a lone pair of electrons, the lone pair may be used to bond with;
-a H+ ion, when the amine is acting as a base
-an electron deficient carbon atom, when the amine is acting as a nucleophile
wwhat ability means that amines can act as a base? (1)
amines can accept a proton so they are Bronsted - Lowry bases
describe the reactions of amine as bases. (2)
amines react with acids to form salts, the products are ionic compounds that will crystalise as the water evaporates. If a strong base like sodium hydroxide is added, it removes the proton from the salt and regenerates the insoluble amine.
what does the strength of a base depend on? (1)
how readily it will accept a proton, both ammonia and amines have a lone pair of electrons that attract a proton.
what is the inductive effect? (1)
alkyl groups release electrons away from the alkyl group and towards the nitrogen atom, this is the inductive effect
what effect does the inductive efffect as on the alkyl group? (1)
increases the electron density of the nitrogen atom and therefore makes it a better electron pair donor (more attractive to protons) so, primary alkylamines are stronger bases than ammonia.
why is a secondary amine a stronger base than a primary amine? (1)
because it has two inductive effects
why is a tertiary amine a less stronger base than a secondary amine? (1)
because it is less soluble in water
why are arylamines less stronger bases than ammonia? 91)
aryl groups withdraw electrons from the nitrogen atom because the lone pair of electrons overlaps with the delocalised system on the benzene ring
what makes amines a nucleophile? (1)
the lone pair of electrons from an amine will attack positively charged carbon atoms.
describe the reaction of ammonia with halogenoalkanes. (2)
primary aliphatic amines are produced when halogenoalkanes are reacted with ammonia, there is a nucleophilic substitution of the halide by NH2. the primary amine produced is also a nucleophile and this reacts with the halogenoalkane to produce a secondary amine. the secondary amine reacts to give a tertiary amine. this will react to give a quaternary ammonium salt
MECHANISM IS ON PAPER
How are primary amines prepared from halogenoalkanes? (1)
by reduction of nitriles
explain the first step of reduction of nitriles to make primary amines. (1)
halogenoalkanes react with cyanide ion in aqueous ethanol. The cyanide ion replaces the halide ion by nucleophilic substitution to form a nitrile
