Properties of Amines Nitrogen with three different substituents is chiral Chiral amines cannot be resolved because the two enantiomeric forms rapidly interconvert by a pyramidal inversion Inversion occurs by momentary rehybridization of nitrogen atom to planar,sp2 geometry,to give planar intermediate Rehybridization of planar intermediate occurs giving the tetrahedral, sp3 geometry Barrier to inversion is about 25 kJ/mol sp3-hybridized sp2-hybridized sp3-hybridized (tetrahedral) (planar) (tetrahedral)
Nitrogen with three different substituents is chiral ▪ Chiral amines cannot be resolved because the two enantiomeric forms rapidly interconvert by a pyramidal inversion ▪ Inversion occurs by momentary rehybridization of nitrogen atom to planar, sp2 geometry, to give planar intermediate ▪ Rehybridization of planar intermediate occurs giving the tetrahedral, sp3 geometry ▪ Barrier to inversion is about 25 kJ/mol Properties of Amines
Properties of Amines Alkylamines are starting materials for insecticides and pharmaceuticals Labetalol is a B-blocker used for the treatment of high blood pressure Prepared by SN2 reaction of an epoxide with a primary amine OH H2N H2N CH3 HO HO Labetalol
Alkylamines are starting materials for insecticides and pharmaceuticals ▪ Labetalol is a b-blocker used for the treatment of high blood pressure ▪ Prepared by SN2 reaction of an epoxide with a primary amine Properties of Amines
Properties of Amines Amines with fewer than five carbons are generally water- soluble Amines form hydrogen bonds and are highly associated H-bonding results in higher boiling points than alkanes of similar molecular weights Amines possess characteristic odors
Amines with fewer than five carbons are generally watersoluble ▪ Amines form hydrogen bonds and are highly associated ▪ H-bonding results in higher boiling points than alkanes of similar molecular weights ▪ Amines possess characteristic odors Properties of Amines
18-3 Basicity of Amines Chemistry of amines dominated by the lone pair of electrons on nitrogen Lone pair makes amines both basic and nucleophilic Electrostatic potential surface of trimethylamine shows in red the region where the nonbonding electrons of nitrogen are located 中9=n+话 An amine An acid A salt (a Lewis base)
Chemistry of amines dominated by the lone pair of electrons on nitrogen ▪ Lone pair makes amines both basic and nucleophilic ▪ Electrostatic potential surface of trimethylamine shows in red the region where the nonbonding electrons of nitrogen are located 18-3 Basicity of Amines
Basicity of Amines Amines are much stronger bases than alcohols and ethers Base strength measured by basicity constant,K RNH2+H2O→RNH3++OH Kb [RNH3+J[OH-] [RNH2] pKb =-log Kb
Basicity of Amines Amines are much stronger bases than alcohols and ethers ▪ Base strength measured by basicity constant, Kb