Chapter 26 - Compounds containing the carbonyl group
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what intermolecular forces exist between carbonyl compounds and why
the C=O group is highly polar which means that dipole dipole forces exist between molecules
what is the trend in boiling point as chain lkength of carbonyls increases
increases as chain length increases
compare the boiling point of carbonyls with alkanes and alcohols
higher than alkanes due to dipole dipole forces but lower than alcohols as no h-bonding occurs
describe the solubility of carbonyls in water as chain length increases
shorter chain are very soluble because h-bonds can form between water and the c=o group as length increases solubility decreases
why is the carbonyl group reactive
because of the high electronegativity difference between carbon and oxygen which makes the bond highly polar this allows nucleophiles to attack the delta positive carbon atom
why is the additon reaction of carbonyls and cyanide ions important
the carbon chain length increases by 1
why is hydrogen cyanide not used for addition reactions with carbonyls
because it is a toxic gas which makes it hard to stop it escaping
why do additon reactions with carbonyls have a chance to give a racemic mixture
because the R-C=O group is planar so the nucleophile can attack from either above or below to give enantiomers
what is responsible for the change in colour of fehlings solution when an aldehyde is present
the Cu2+ ion is blue and then forms Cu2O which is red upon reduction
what ion is present in tollens reagent before reaction
aqeous ammonia and diaminesilver for the complex ion (Ag(NH3)2)+
what are the products of the tollens test
carboxylic acid, silver, and NH3
what is the reagent that will reduce carbonyls and what ion does it contain
sodium tetrahydroborate contains H- ions (hydride ions)
what kind of reactions occur when carbonyls are reduces
nucleophilic addition
why is the c=o bond reduced by hydride ions but not the c=c bond
because the c=o bond is polar and the hydride ion is attracted to the delta positive carbon in c=c there is a high electron density throughout the bond which repels the hydride ion
why are carboxylic acids weak acids
because they only partically ionise in solution
why are carboxylic acids soluble in water
because the oh group allows h-bonds to form between water and the acid molecuels
why do carboxylic acids have much higher melting points than alkanes of similar mass
because hydrogen bonds are able to form between molecules which are stronger than dipole diple and van der waals forces
what are 2 carboxylic acid molecules h-bonded together called
a dimer
what pieces of apparatus can be used to identify a carboxylic acid by its melting point
a thiele tube, thermometer, capillary tube
how do you name an ester
the first part of the name comes from the alkyl group on the oxygen and then the carboxylic part of the moecule comes after with the sufflix -oate
what kind of organic molecule are fats and oils
esters with long carbon chains
why are esters suitable for use in perfumes and flavouorings
the molecules are fairly volatile and often have a pleasant smell
what remains when the hydrogen on the oh group is lost on a carboxylic acid
a carboxylate ion and a proton (h+)
what catalyst is used to form and hydrolyse esters
strong acid catalyst such as such as concentrated sulfuric acids