Topic 17 - PPQs
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What does brady’s test for?
C=O associated with ONLY aldehydes and ketones
product of a positive test of 2-4 dnph contains which bond?
C=N
reagents and conditions for converting ethanal (by two step synthesis) to 2-hydroxypropanoic acid
HCN in presence of KCN dilute HCL, under reflux
What does H- have
a lone pair
mechanism for reduction of propanone to propan-2-ol
step 1: H- has lone pair, curly arrow form H- to C in C=O, arrow from C=O bond to O, dipoles step2: dipoles on water, curly arrow from O- to H in water, curly arrow from O-H bond to O in water, lone pair on O-
test to distinguish between carboxylic acid and alcohol
sodium carbonate - fizzing if carboxylic acid (production of CO2)
explain why the order of boiling points is this ethanoic acid > ethanol > ethanal [3]
mp1 - ethanal has no H bonds mp2 - H bonds in ethanol are stronger than london forces in ethanal mp3 - ethanoic acid forms dimers
what intermolecular forces are present in: • ethanal • ethanol • ethanoic acid
• london forces • london forces, ,H bonds • london forces, , H bonds, form dimers XXXXX
Fehlings or…
benedicts
what do u do w fehlings/benedicts
warm with
Explain why it is necessary to use HCN and KCN in the carbonyl + HCN mechanism?
the KCN provides the :CN- nucleophile
explain why the product of the carbonyl + HCN is not optically active
• bonds around C=O planar • nucleophile attacks from both sides (above and below) • forming a racemic mixture
other than spectroscopy how would you use ppt from a chemical test to identify sm
• measure melting point - compare against known data
technique used to purify product of test with 2-4dnph
recrystallisation
explain why old stocks of aldehydes often react with sodium carbonate solution
they contain carboxylic acids which have formed by oxidation of the aldehydes (from the air)
carboxylic acid + sodium carbonate
salt + water + CO2
butanoic acid as an acyl chloride
butanoyl chloride
two conditions for alcohol + carboxylic acid —-> ester + water
• H2SO4 - HEAT
identify another chemical that could be added to methanol to make methyl butanoate
butanoyl chloride because alcohol + acyl chloride –> ester + HCl
state 2 advantages of and 1 disadvantage acyl chloride + alcohol —> ester + HCl VS carboxylic acid + alcohol –> ester + water
advantages of acyl chloride + alcohol —> ester + HCl 1) goes to completion 2) no catalyst needed disadvantage 1) acyl chloride difficult to store and more expensive
Naming carboxylic acids - which C is the first C
the carbon in the C=O bond
where is the hydrogen bond from and to
from the O-H bond to the IIIIIIIIII between the H and lone pair on oxygen
Describe how london forces are formed
instantaneous dipole induced dipole
explain boiling point differences between straight chain and branched chain alcohols
• straight chain higher • because branching weakens london forces • because less SA so molecules can’t get as close