Ch.26 carbonyls and carboxylic acids
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carbonyl functional group
C=O
aldehyde
H - C = O. -al
ketone
C. -one l C=O l C
do ketones or aldehydes go through oxidation reactions
ketones no aldehydes yes
what type of reaction do carbonyl compound go through
nucleophilic addition slight + O of C=O attracts nucleophiles
reducing agent
[H]
NaBH4
reducing agent ro reduce ketones and aldehydes to alcohols
how can u increase the length of a carbon chain
HCN H and CN from H2SO4 and NaCN
hydroxy nitrile
OH-C=_N
mechanism for the reaction of NaBH4
contains hydride ion H+ attracted to and donated to the part + C in C=O dative covalent bond formed (arrow from H: to C of C=O) pi bond breaks by heterolytic fission (arrow from double bond to O) - charged intermediate O of the intermediate donates a lone pair to a H in a water molecule (arrow from O: to H of water and arrow from H-O bond of water to O) forming an an alcohol + OH-
mechanism for NaCN/H+
cyanide ion attacks e- deficient C (arrow from CN: to C) forms dative covalent bond pi bond breaks by heterolytic fission (arrow from = to O) - charged intermediate protonated by donating lone pair to a H+ (arrow from O: to H+)
how do u detect a carbonyl compound
2,4-dinitrophenylhydrazine 2, 4-DNP (Brady’s reagent) in the presence of a carbonyl group a yellow/orang precipitate will form 2,4-dinitrophenylhydrazone usually dissolved in ethanol and sulfuric acid
how to distinguish between ketone and aldehydes
tollens reagent 3cm depth AgNO3 (aq) NaOH (aq) until brown precipitate forms Ag2O add dilute NH3 until brown precipitate dissolves forming a clear solution in a clean test tube add equal parts tollens reagent and unknown solution leave test tube in beaker of warm water 50*C for 10-15 mins if aldehyde a silver mirror will form ketones wont react
how does tollens reagent create a silver mirror
contains silver ions Ag+ act as an oxidising agent in the presence of ammonia aldehyde oxidised to carboxylic acid sliver ions reduced to silver forming the silver mirror
identifying aldehydes and ketones by melting point
2, 4-DNP precipitate is filtered and recrystalised melting point is messured and compared to a known database
solubility of carboxylic acids
C=O and O-H bonds are both polar so they can form hydrogen bonds with water molecules soluble in water up to 4 carbon atoms as carbons increase solubility decreases as non polar carbon chain has greater effect on overall polarity
strength of carboxylic acids
weak acids partially dissociate
what reactions do carboxylic acids take place in
redox with metals neutralizations with bases forming carboxylate salts
how to test for carboxyl group
only common organic compound acidic enough to react with carbonates
what is a carboxylic acid derivative
a compound that can be hydrolyzed to form the parent carboxylic acid they all contain an acyl group R-C=O |
ester
R-C=O | O-R
acyl chloride
R-C=O | CL
acid anhydride
R-C=O | O-C=O | R
amide
R-C=O | NH2