Nucleophilic addition

• Primary alcohols can be oxidised to aldehydes
• Secondary alcohols can be oxidised to ketones
• If an aldehyde is reduced, a primary alcohol will be obtained
• If a ketone is reduced, a secondary alcohol will be produced
• Reducing agents of aldehydes and ketones used are:

  • lithium tetrahydridoaluminate (LiAlH4) dissolved in non-aqueous solvents like epoxyethane
  • sodium tetrahydridoborate (NaBH4) dissolved in aqueous ethanol
• [H] can represent a reducing agent
• The C=O contains a highly electronegative oxygen atom, reslting in the carbonyl bond being polar
• The carbon atom in carbonyl groups is electron deficient and is prone to attack by a nucleophile, which has a readily available lone pair of electrons
• A hybride ion is a nucleophile because it has a lone pair of electrons
• Carbon can have a maximum of four covalent bonds
• Step 1 of nucleophilic addition leads to the formation of an intermediate
• The intermediate of nucleophilic addition contains the hybride ion, which has formed a new C-H bond
• The intermediate contains a carbon-oxygen single bond and the oxygen contains a negative charge and an additional lone pair of electrons
• The intermediate reacts with a hydrogen ion (H+) to form an alcohol
• The hydrogen ion in nucleophilic substitution comes from the aqueous solution or the addition of a dilute acid
• Nucleophilic addition:

  • A hybride nucleophile attacks the carbon of the C=O, resulting in a C-H bond
  • This causes the double bond to break
  • An intermediate has now been formed
  • The oxygen now contains a negative charge and reacts with H+ to form an alcohol
• Aqueous HCN is generally considered a poor source of cyanide ions, since it doesn't dissociate readily. Instead, a cyanide salt (e.g. NaCN) is used since this dissociates readily in the presence of water
• A cyanide salt is diluted with sulfuric acid to provide the source of H+ ions
• The final organic product can form a racemic mixture due to a planar double bond. This means there is equal opportunity for attack
• Hydrogen cyanide is dangerous
• A cyanide ion is a type of polyatomic ion
• Usually in polyatomic ions, you put the negative charge above the most electronegative ion EXCEPT in the case of cyanide ion, where the negative charge is above the carbon
• Cyanide ions are not considered organic compounds
• hydrogen cyanide is not a metal salt, unlike KCN and NaCN. Instead it is covalently bonded
• When cyanide reacts with an aldehyde or ketone, a molecule producing both an alcohol and nitrile group is formed. These are called hydroxynitriles
• The conditions of the production of hydroxynitriles are:

  • a source of cyanide ions (dissolved in water)
  • dilute H2SO4
• Potassium cyanide ingested is deadly and could react to form hydrogen cyanide gas, which is deadly
• In the intermediate of nucleophilic addition, then oxygen will have a negative charge because it has gained a lone pair of electrons
• the reduction of aldehydes and ketones is a type of nucleophilic addition
• The production of hydroxynitriles is an example of nucleophilic addition
• When naming hydroxynitriles, count the carbon in the nitrile group as position number one in the carbon chain
• Unsymmetrical ketones undergo nucleophilic addition and reduction to form optical isomers
• Aldehydes generally form optical isomers when undergoing nucleophilic addition. This is unless it is undergoing reduction
• Nucleophilic addition forms a racemic mixture