module 6 organic

• carbonyl functional group includes aldehydes and ketones that both contain a C=O bond
• in aldehydes the carbonyl is found at the end of the chain, and is written as CHO, methanal :

  
• methanal = formaldehyde, used in solution to preserve biological specimens
• in ketones the carbonyl functional group is joined to 2 carbon atoms in the carbon chain, written as COe
• in ketones, carbonyl group is joined to 2 carbon atoms, ketone group is written as CO
• simplest keton is propanone, CH3COCH3, also known as acetone, used as an important industrial solvent and nail polish removers

  
• reactivity of aldehydes and ketones is influenced by the nature of the carbon-oxygen double bond, which is made up of both a sigma bond and a pi bond

  
• C=C in alkenes is non polar
• C=O in carbonyl compounds is polar
• oxygen is more electronegative than carbon so the electron density lies closer to it than to the carbon, making the C more positive and the O more negative, so aldehydes and ketones react with some nucleophiles
• nucleophile is attracted to and attacks the slightly positive carbon resulting in addition across the C=O double bond
• carbonyl groups undergo nucleophillic additions
• alkenes with the non polar C=C bond react with electrophiles and undergo electrophillic addition
• aldehydes are reduced to primary alcohols by NaBH4, e.g butanal is reduced to butan-1-ol

  
• ketones are reduced to secondary alcohols by NaBH4, e.g propanone is reduced to propan-2-ol

  
• sodium tetrahydridoborate (III) is used as a reducing agent to reduce aldehydes and ketones to alcohols, the aldehyde or ketone is warmed with the NaBH4 in aqueous solution
• carbon atom in the C=O is electron deficient and attracts nucleophiles, aldehydes and ketones both react by nucleophillic addition to form alcohols