Amines Flashcards
Why are the bond angles in ammonia 107 degrees?
Because the lone pair on the nitrogen repels more than the bonding pairs of electrons in the N-H bonds and so the bond angle is reduced from 109 to 107
Why are boiling points of amines lower than those of alcohols?
Because the hydrogen bonds formed between -NH2 groups are weaker than hydrogen bonds formed between -OH groups in alcohols because nitrogen is less electronegative than oxygen
Why are short chain primary amines soluble in water and alcohols?
Because they form hydrogen bonds with these solvents
Why is phenylamine not very soluble in water?
Because the benzene ring cannot form hydrogen bonds
What can the lone pair in amines be used to form a bond with?
An H+ ion, when the Amine is acting as a base
An electron-deficient carbon atom, when the Amine is acting as a nucleophile
Are amines Brønsted-Lowry acids or bases?
Amines are Brønsted-Lowry bases because they can accept a proton
What do bases react with acids to form?
Salts
What is the inductive effect?
Where alkyl groups release electrons away from the alkyl group and towards the nitrogen atom
What effect does the inductive effect have on the electron density on the nitrogen atom?
The inductive effect of the alkyl group increases the electron density on the nitrogen atom and therefore makes it a better electron pair donor (I.e. More attractive to protons)
Why are secondary alkylamines stronger bases than primary alkylamines?
Because they have two inductive effects
Why are tertiary alkylamines not stronger bases than secondary ones?
Because they are less soluble in water
What effect do aryl groups have on the electron density of on the nitrogen atom?
Aryl groups withdraw electrons from the nitrogen atom because the lone pair of electrons overlaps with the delocalised system on the benzene ring. The nitrogen is a weaker electron pair donor and therefore less attractive to protons
Describe how amines can be formed by the reduction of nitriles
(1. ) Halogenoalkanes react with the cyanide ion in aqueous ethanol. The cyanide ion replaces the halide ion by Nucleophilic Substitution to form a nitrile
(2. ) nitriles contain the functional group C==N. they can be reduced to primary amines with a nickel/hydrogen catalyst
Why does the reduction of nitriles produce a purer product than the Nucleophilic Substitution of Halogenoalkanes and ammonia?
Because only the primary Amine can be formed
What is phenylamine made from in industry?
It is made from benzene produced from crude oil?
