Paper 2 Flashcards
(37 cards)
What is a reason for heating under reflux?
To prevent any substances escaping
What does D20 do?
Removes NH2 and OH - peaks will disappear. NH2 and OH protons are both labile and will exchange with deuterium in a D20 shake
Apart from recycling, state 2 other methods for usefully processing waste polymers
- Combustion for energy production
- Use as an organic feedstock for production of plastic and other organic chemicals
Plan an experiment that would allow the student to confirm the identity of the pure organic product by means of a chemical test
React (sample of distillate) with 2,4-dinitrophenylhydrazine (or 2,4-DNPH)
recrystallise AND determine the melting point
Compare melting point to known/library value for
cyclohexanone (derivative)
Can carboxylic acids be hydrolysed? Can CH3COCl be hydrolysed?
Carboxylic acids cannot be hydrolysed.
CH3COCl can be.
CH3COCl + H20 –> CH3COOH + HCl
CH3CH2Cl reacts with an excess of ethanolic NH3. What is the main organic product and why?
CH3CH2NH2 because excess NH3 prevents further substitution to secondary or tertiary amines.
What does alicyclic mean?
carbon ring with no aromatic character
Nucleophilic substitution takes place faster using a different haloalkane than 1-bromobutane to give same product.
Identify this haloalkane and explain your answer.
1-iodobutane
AND
C–I bonds are weaker (than C-Br)
OR C–I bond has a lower bond enthalpy
OR C–I bond needs less energy to break
Is the lid on or off during distillation?
ON - it is off for reflux
A student adds bromine water to a solution of phenol. What would the student see during this reaction?
Bromine water goes from orange to colourless and a white precipitate is formed.
Describe a method to obtain a pure, dry sample of alkene B from a liquid reaction mixture of organic products and the acid catalyst
- Use of a separating funnel to
separate organic and aqueous
layers - Drying with an anhydrous salt, e.g.
MgSO4, CaCl2, etc. - Redistillation
What are the limitations of free radical substitution?
- Further substitution of halogen
- Substitution at different positions on chain to give mixture of structural isomers
Describe the bonding in the model of benzene
- p-orbitals overlap to form π bonds
- (π-)electrons are delocalised
Explain why chlorine reacts much more readily with C6H5N(CH3)2 than with benzene
(In C6H5N(CH3)2)
(lone) pair of electrons on N is (partially) DELOCALISED into the ring
electron density increases/is higher (than in benzene)
ORA
Cl2/electrophile is (more) polarised ORA
Determine the nature of acidity of acyl chlorides
Hydrolyse in water to form a strong acid.
CH3COCl + H20 —> CH3COOH + HCl
Draw a diagram to show how p-orbitals are involved in the formation of a Pi-bond.
p-orbital bell shape (vertical) above and below carbon atoms - dont overlap.
then horizontal oval shape above and below the carbon bond
Why can the NH2 group react with dilute hydrochloric acid?
Nitrogen electron pair OR nitrogen lone pair
AND
accepts a proton/H+
Suggest a reason why polyesters are biodegradable
Ester bond/linkage can be hydrolysed
Suggest how HBr can act as an electrophile
(The H atom of HBr) accepts a pair of electrons
How will the melting point of an impure compound differ from its pure form?
MP will be lower (weaker IMF) and broader/larger range. Measured using a melting point apparatus
State and explain how the halogen in the haloalkane affects rate of hydrolysis
Links rate of reaction to strength of bond/bond
enthalpy
e.g.
the weaker the bond the faster the reaction
stronger bond takes longer to break
lower bond enthalpy reacts faster
Correct comparison of rate of reaction for at least
two C–Hal bonds
e.g.
C–F bond is hydrolysed slowest
C–I bond is hydrolysed faster than C–Br
C–Br has shorter reaction time than C–Cl
OR
Correct comparison of C–Hal bond strength/enthalpy
of at least two of C–Hal bonds
e.g.
C–I bond is the weakest
C–I has lower bond enthalpy than C–Br
C–Br is broken more easily/readily than C–Cl
C–Hal bond strength decreases down group (7)
A polyester is formed from 200 molecules of 4-hydroxybenzoic acid.
What is the relative molecular mass, Mr, of the polyester?
Relative mass of 200 molecules = 200 × 138 = 27600
Mr of polyester = 27600 – 199 × 18 = 24018
Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekule and delocalised model of benzene. (3)
Similarities:
- (sideways) overlap of p orbitals
- π bond/system/ring above and below (bonding (C) atoms/ring/plane)
Difference:
Kekule has: alternating π bonds OR 3 π bonds /
localised (π electrons) / overlap in one direction /
2 electrons in π bond
AND
Delocalised has: π ring (system) / all p orbitals
overlap OR (π electrons) spread around ring / overlap in both directions / 6 electrons in π bond
What does a curly arrow show in a reaction mechanism?
Movement of an electron pair
