[26.1] carbonyl compounds

• carbon-oxygen double bond • bond is polar due to difference in electronegativity

• carbon atom of carbonyl group is attached to 1 or 2 hydrogen atoms • structual formula functional group = CHO

• carbonyl functional group is joined to 2 carbon atoms • structural formula functional group = CO

• carbon atom of carbonyl group is always designated as carbon-1 • suffix is -al

• find longest carbon chain for stem • lowest number suffix where -C=O functional group is found (eg. C2 = -2-) • ends in -one (eg. pentan-2-one)

• overlaps with a 2p orbital of oxygen to form a pi bond • bond is polar as oxygen is more electronegative than carbon

• oxidation of primary alcohols • RCH₂OH + [O] -> RCHO + H₂O

• oxidation of secondary alcohols • RCHOHR + [O] -> RCOR + H₂O

• forms carboxylic acids • reflux with acidified dichromate (VI) ions, Cr₂O₇²⁻/H⁺ • potassium dichromate (VI), K₂Cr₂O₇ / dilute sulfuric acid, H₂SO₄ • RCHO + [O] -> RCOOH

• ketones do not undergo oxidation reactions • this lack of reactivity provides chemists with a way of distinguishing between aldehydes and ketones

• NaBH₄ is used as reducing agent to reduce aldehydes and ketones to alcohols • need H₂O and heat • [H] = reducing agent

• aldehydes are reduced to primary alcohols by NaBH₄ • RCHO + 2[H] -> RCH₂OH

• ketones are redued to secondary alcohols by NaBH₄ • RCHOHR + 2[H] -> secondary alcohol

• add H-CN across C=O in aldehydes and ketones • useful to increase C chain length • HCN is too hazardous so NaCN/H₂SO₄ used • forms hydroxynitrile (eg. 2-hydroxybutanenitrile = CH₃CH₂CH(OH)CN) • organic product contains -OH hydroxyl group and nitrile group, C≡N

• NaBH₄ can be considered as containing the hydride ion, :H-, which acts as the nucleophile • lone pair of electrons from hydride ion is attracted and donated to the partial positive C of carbonyl • dative covalent bond forms between H and C, pi bond breaks, forming a negatively chargd intermediate • lone pair of electrons on O atom is attracted to partial positive H in water molecule and formed a covalent bond • intermediate is protonated to form an alcohol • hydroxide ion, OH-, is left

• weakly acidic covalent molecule • very poisonous gas with low bp • generated from reaction of NaCN/KCN (aq) with sulfuric acid

• weakly acidic solution strengthen polarity in C=O • resulting solution contains free -CN ions and H+ (aq) from HCN

• lone pair of electrons from cynanide ion, :CN-, is attracted and donated to δ+ carbon atom in carbonyl C=O double bond • a dative covalent bond forms • pi bond in C=O double bond breaks by heterolytic fission forming a negatively charged intermediate • intermediate is protonated by donating a lone pair of electrons to a hydrogen ion to form the product • product is a hydroxynitrile