Amines

• Functional group of amines

  -NH2
• Structure of propan-1-amine

  CH3-CH2-CH2(NH2)
• Structure of N-methylethanamine

  CH3 -NH-CH2-CH3

  
• Why do ammonia and amines act as Brønsted-Lowry bases?

  They can accept protons
• What is the base strength determined by?

  The base strength is determined by the availability of the lone pair of electrons on the nitrogen

  atom
• Why are primary amines stronger bases than ammonia?

  The alkyl group pushes electron density towards the nitrogen via the inductive effect

  This makes the lone pair of electrons on the nitrogen atom more available for donation to

  a hydrogen ion.

  This makes the primary amine a stronger base (better at accepting protons)
• What about the base strength of secondary amines and tertiary amines?

  They increase due to more alkyl groups pushing electron density but the increase after 3 carbon chain length is negligible
• Why are aromatic amines weaker bases than ammonia?

  The lone pair of electrons on the nitrogen atom are less available because they are delocalised with the benzene ring
• How do you produce primary amines?

  Halogenoalkanes react with excess ammonia (NH3)

  Excess ammonia reduces further nucleophilic substitution
• How are quaternary ammonium salts useful?

  Cationic surfactants in fabric and hair conditioners
• How can primary amines also be produced?

  Reducing nitriles via LiAlH4 or hydrogen gas with a nickel catalyst
• How can aromatic nitro compounds be converted into aromatic amines?

  Reduction using tin and concentrated HCl
• Why is NH2Cl weaker base than NH3?

  The chlorine atom is electron withdrawing from the nitrogen atom, making the lone pairs on the nitrogen atom less available for donation to a proton
• Why are primary amines with chain lengths up to about four carbon atoms are very soluble both in water and in alcohols?

  Form hydrogen bonds
• What about primary chains longer than four carbon chain length?

  Relatively insoluble, so supplied as hydrochlorides
• What are aspirin and paracetamol?

  N-substituted amide