3.8 carbonyls aldehydes and ketones

• what are carbonyls?

  compounds with a C=O bonds
• describe the intermolecular forces in carbonyls?

  pure carbonyls can't hydrogen bond to themselves however they can produce permanent dipole forces , the C=O bond Is polarised
• describe the solubility of carbonyls:

  smaller carbonyls are soluble in water due to hydrogen bonding with the water molecules
• how do reactions with carbonyls occur?

  the C=O bond is polarised so the partially positive carbon attracts nucleophiles
• why don't C=O bonds undergo addition reactions as easily like C=C bonds?

  because they are stronger
• what are 2 examples of carbonyls?

  aldehydes and ketones
• what is the oxidising agent used to oxidise alcohols?

  K2Cr2O7 - potassium dichromate
• write out word equations for the oxidation of primary alcohols and secondary alcohols :

  • primary alcohol + [O] -> aldehyde -> carboxylic acid
  • secondary alcohol + [O] -> ketones
• what are the products of the reduction of carbonyls?

  alcohol
• what reducing agents are used?

  NaBH4 and LiAlH4
• describe what happens when a carbonyl is reduced using NaBH4

  • what's the reagent
  • what conditions
  • what is the name of the mechanism

  1. NaBH4 in aqueous ethanol
  2. room temperature and pressure
  3. nucleophilic addition
• what is another way to reduce carbonyls?

  name

  reagents

  condition

  catalytic hydrogenation

  hydrogen and nickel catalyst

  high pressure
• describe the nucleophilic addition of carbonyls using NaCN or KCN

  • reagent
  • condition
  • product
  • where do the ions come from
  • why don't we use HCN
  • what are the advantages of using NaCH and KCN
  • NaCN or KCN and dilute sulphuric acid
  • room temperature and pressure
  • hydorxynitriles
  • :CN- from the KCN or NaCN and H+ from the H2SO4
  • its produces a toxic gas which is hard to contain
  • you get a higher concentration of cyanide ions as the compound fully ionised however with HCN, it will partially ionise as its a weak acid
• outline the nucleophilic addition mechanism using NaBH4 :


  outline

  
• draw the nucleophilic addition mechanism using cyanide ions


  outline

  
• in a reduction reaction, where does the :H- ion come from and H+ ion come from?

  :H- from NaBH4 and H+ from water or weak acid