chem2206

• Epoxides


  Three membered-cyclic ether, also called oxirane
• Epoxides


  • Valuable synthetic intermediates used for converting alkenes to a variety of other functional groups
• Conversion of alkene to epoxide

  Reaction with peroxyacid, RCOOOH
• Peroxyacid


  Carboxylic acid that has an extra oxygen atom in a -O-O- (peroxy) linkage
• Epoxide nomenclature (common name)


  Formed by adding "oxide" to the name of the alkene that is oxidised
• Epoxide nomenclature (systematic)


  Named as derivatives of the parent compound, ethylene oxide, using "oxirane" as the systematic name for ethylene oxide
• Epoxide synthesis (from alkenes)

  Reaction with peroxyacids, RCOOOH
• Epoxide synthesis (from halohydrins)

  1. Base promoted cyclization of halohydrins

  2. Intramolecular SN2 attack of internal alkoxide on carbon bearing halogen leaving group
• Halohydrin


  Molecule with halogen bonded to the β-carbon bearing an -OH group
• Halohydrin preparation


  Reaction of alkene with halogen in presence of water
• Other cyclic ethers


  • Oxetanes
  • Furans (oxolanes)
  • Pyrans (Oxanes)
• Epoxide reacts with Grignard reagent

  Produces alcohol bearing two more carbons than the parent Grignard molecule
• First test for epoxides: Stereochemistry to alcohols
• Amines

  A class of organic compound of general formula: RNH2, where R is an alkyl or aryl group
• Amine structure

  • Similar to ammonia (NH3), with nitrogen sp3 hybridised
  • Bond angle larger than ammonia due to greater Van der Waals repulsion
• Amines

  • Propylamine
  • Trimethylamine
• Amine nomenclature

  • Follow IUPAC convention
  • Select longest continuous carbon chain as root name
  • Change ending e in alkane to amine
  • Number position of amino group
  • Name substituents in alphabetical order
• Amine classification

  Primary, secondary, tertiary, quaternary
• Amine physical properties

  • Polar molecules with dipole moments
  • Hydrogen bond donors and acceptors
  • Tertiary amines have lower boiling points than primary/secondary
  • Amines soluble in alcohols and lower molecular weight in water
  • Characteristic fishy odour
• Amine basicity

  • Amines can act as nucleophiles and bases
  • Basicity expressed by basicity constant Kb
• Amine preparation

  1. From alkyl halides

  2. From nitriles using LiAlH4

  3. From Schiff bases and oximes using LiAlH4
• Reactions of aliphatic amines


  1. With acid chlorides to form amides

  2. Formation of diazonium compounds with nitrous acid

  3. Diazonium salt reactions like hydrolysis, Sandmeyer, etc.

  4. Amines as leaving groups in Hofmann elimination
• Reactions of amines with aldehydes and ketones

  1. Form carbinolamines which dehydrate to Schiff bases

  2. Specific products formed depending on amine type
• Aldehydes


  Compounds with general formula RCHO
• Ketones


  Compounds with general formula RCOR'
• Nomenclature of aldehydes and ketones

  • Select the longest continuous carbon chain
  • Indicate the position of the functional group, using the lowest number
  • Start numbering the carbon from the end that has the functional group
  • Substituents are named in alphabetical orders
  • Whenever, there are more than one substituent of the same type, use di, tri, tetra or penta
• Polar molecules


  Molecules that have a net dipole moment
• Aldehydes and ketones are polar molecules because there is charge separation
• Physical properties of aldehydes and ketones

  • Soluble in polar organic solvents, such as ethanol, water etc.
  • Cannot function as H-bond donors to one another or other molecules such as H2O and alcohols
  • Can only function as H-bond acceptor
  • Boiling points are lower than those of alcohols of similar molecular weight
  • Can act as H-bond acceptor with an hydrogen from H2O or from an alcohol molecule
  • Good solvents for polar hydroxylic compounds such as the alcohol
  • Remarkably soluble in water
  • As the hydrocarbon chain length increases, hydrophobicity increases and hence aldehydes and ketones become less soluble in water
• Preparation of aldehydes and ketones from alcohols

  1. Oxidation of primary and secondary alcohols

  2. Use of mild oxidant like PCC to stop at aldehyde stage

  3. Swern oxidation to oxidise primary alcohol to aldehyde
• Preparation of aldehydes and ketones via ozonolysis of alkenes


  1. Alkenes react with ozone to yield an ozonide

  2. Ozonide treated with dimethylsulphide yields a mixture of an aldehyde and ketones
• Reactions of aldehydes and ketones

  • Undergo nucleophilic addition
  • Aldehydes are more reactive than ketones towards nucleophilic addition due to steric and electronic effects
• Reaction with Grignard reagents

  1. RMgX + HCHO -> RCH2OH + MgBrOH

  2. RMgX + RCHO -> RCHR'OH + MgBrOH

  3. RMgX + R2C=O -> RCR'R''OH + MgBrOH
• Reaction with HCN

  1. Aldehyde reacts with HCN to yield a b-hydroxycyano compound

  2. b-hydroxycyano compound can be hydrolysed to yield a b-hydroxycarboxylic acid
• Clemmensen reduction

  Carbonyl group of aldehydes and ketones reduced to a methylene unit using Zn with Hg/HCl
• Wolff Kishner reduction

  Carbonyl group of aldehydes and ketones reduced to a methylene unit using hydrazine, N2H4 and a base
• Reaction with H2O

  Aldehydes and ketones react with acidified water to yield a dihydroxy compound
• Reaction with alcohols

  1. Aldehydes react with one mole of an alcohol to form a hemi-acetal

  2. Aldehydes react with two moles of an alcohol to form an acetal
• Reaction with NH3 and NH3 derivatives

  1. Aldehydes and ketones react to form a condensation product called a carbinolamine

  2. Carbinolamine on dehydration yields a Schiff's base type compound
• Reaction with Tollens reagent

  Silver ion, Ag+ oxidises aldehydes selectively in a convenient functional group test for aldehydes