Flashcards

Interactive study deck for amines, basicity, and synthetic routes.

Amines: read all 18 questions and answers

Define a primary amine.
An organic compound in which one hydrogen atom of ammonia has been replaced by an alkyl or aryl group (RNH₂).
What is the molecular formula of phenylamine?
C₆H₅NH₂
Why do amines behave as weak bases?
The nitrogen atom has a lone pair of electrons that can accept a proton (H⁺) to form a dative covalent bond.
Arrange the following in order of increasing basicity: ammonia, ethylamine, phenylamine.
Phenylamine < ammonia < ethylamine
Explain why ethylamine is a stronger base than ammonia.
The ethyl group is electron-donating (positive inductive effect), which increases the electron density on the nitrogen atom, making the lone pair more available to accept a proton.
Explain why phenylamine is a weaker base than ammonia.
The lone pair on the nitrogen atom is partially delocalised into the benzene ring's pi-electron system, making the lone pair less available for protonation.
What reaction conditions are required to produce a primary amine in high yield from a halogenoalkane and ammonia?
Excess ammonia dissolved in ethanol, heated under pressure in a sealed tube.
Why does reacting a halogenoalkane with ammonia tend to produce a mixture of amine products?
The primary amine produced is itself a nucleophile containing a nitrogen lone pair, so it can react with remaining halogenoalkane molecules in consecutive nucleophilic substitutions.
What organic product is formed when a halogenoalkane reacts with an excess of a tertiary amine?
A quaternary ammonium salt (R₄N⁺X⁻).
What is a cationic surfactant?
A quaternary ammonium salt containing at least one long hydrophobic hydrocarbon chain, used in fabric softeners and hair conditioners.
How do cationic surfactants work on hair or fabrics?
The positively charged ammonium head group binds to negatively charged surfaces of fibers/hair, while the long hydrophobic tail points outwards, smoothing the surface and reducing static.
Write the chemical equation for the first step in the synthesis of propylamine from bromoethane.
CH₃CH₂Br + KCN → CH₃CH₂CN + KBr (forming a nitrile and extending the carbon chain).
What reagent and condition are used to reduce nitriles to primary amines in the laboratory?
Lithium tetrahydridoaluminate (LiAlH₄) in dry ether.
State the advantage of preparing primary amines by reducing nitriles compared to nucleophilic substitution with ammonia.
It produces a pure primary amine with no secondary/tertiary side products, and it increases the carbon chain length by one carbon.
Write the overall equation for the reduction of nitrobenzene to phenylamine.
C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O
State the reagents and conditions used in the first stage of the reduction of nitrobenzene.
Tin (Sn) and concentrated hydrochloric acid (HCl), heated under reflux.
Why is sodium hydroxide added at the end of the reduction of nitrobenzene?
To neutralise the acid and liberate the free phenylamine base from the phenylammonium intermediate salt.
What is the IUPAC name for H₂N-CH₂-CH₂-CH₂-NH₂?
Propane-1,3-diamine

← Back to Topic Hub Exam Practice →