Chemistry Paper 2 Feb 2025
What two types of bond are within an alkene? - Ans>>sigma and pi
sigma bond - Ans>>the direct overlapping of two orbitals
pi bond - Ans>>the sideways overlap of p orbitals
C=C how many pi bonds and sigma bonds are in this - Ans>>one sigma two pi
bonds
what two types of isomers are found in alkenes - Ans>>cis/trans and E/Z
Difference between E/Z isomers and Cis/trans isomers - Ans>>E/Z compares
relative position based in priority groups (IP rules) look at the atomic number of the
first bonded element
Cis/Trans compares the relative positions of identical groups
major and minor products in alkenes - Ans>>the major product forms the most
stable carbocation intermediate during alkene reactions
tertiary>secondary>primary
what type of polymer do alkenes produce? - Ans>>addition polymers
synthesis of an organic liquid - Ans>>once reaction is complete into a separating
funnel. Neutralise any excess acid using sodium carbonate (stops bubbling when all
gone)
Allow 2 layers to settle
Use density into to establish layers. If density into not given, add water to establish
aqueous layer.
(aqueous layer get bigger)
Density of water is 1 anything greater is more dense.
collect the organic layer
add a drying agent to remove small traces of water left in the organic layer (e.g..
anhydrous CaCl2)
If the question tells you the boiling point of the organic liquid say distil dried product
and collect fraction that comes over the boiling point.
3 ways to determine purity of products - Ans>>1. boiling point should match known
data, boils over a narrow range
,or
2. Run TLC, measure Rf value, compare to known data values/Run TLC and compare
to chromatogram of pure sample
or
3. Run NMR/IR/Mass spectrum, compare to spectral database of pure compounds.
How to purify by recrystallisation? - Ans>>-dissolve in a minimum volume of hot
solvent
-cool in ice to recrystallise (impurities stay in solution)
-filter using Büchner flask/reduced pressure filtration
-wash with cold solvent
-dry
Does reflux have an open or closed system? - Ans>>open
overall equation for ozone depletion - Ans>>O3 + O -> 2O2
rate of formation of ozone = - Ans>>rate of breakdown of ozone by UV light =
what type of compound breaks down the ozone layer? - Ans>>chlorofluorocarbons
Initiation reaction of CCl3F
what is the mechanism, equation and why the radicals formed - Ans>>homolytic
bond fission
Cl. + CCl2F.
C-Cl bond broken as its weaker than C-F
Evidence for the structure of delocalised benzene against the kekule structure -
Ans>>-Bond lengths of benzene are the same
-enthalpy of hydrogenation less exothermic than expected
-does not undergo addition reaction
why does benzene need a halogen carrier to undergo electrophilic subsitution? -
Ans>>it is not electron dense enough to polarize the molecule into an electrophile
electrophile - Ans>>electron pair acceptor
what is the catalyst for halogenation of benzene? - Ans>>AlX3
what is the catalyst for nitration of benzene? - Ans>>sulfuric acid
How can you test for a phenol? - Ans>>weak acid that reacts with NaOH but too
weak to react with Na2CO3 so no bubbles of CO2
, why don't you need a catalyst for the halogenation and nitration of phenol? -
Ans>>The lone pair on the oxygen molecule in the hydroxyl group donates its pair
of electrons into the delocalised pi ring. Increases the electron density of the phenol
molecule which allows phenol to polarise HNO3 and X2 molecules to produce an
electrophile
what is the colour change when phenol is halogenated with Bromine molecule? -
Ans>>Br2 is decolourised and a white ppt is formed.
Describe the reactivity if benzene Vs alkenes - Ans>>Benzene, the Pi electrons are
decolourised Pi electron density is low compared to alkene. Benzene is unable to
polarize electrophiles so can't attract them strongly. In C=C of alkenes the Pi
electrons are localised. Pi electron density is high (compared to benzene) able to
polarize electrophiles so attracts them strongly.
which groups are electron donating on benzene? - Ans>>OH and NH2
increase the electron density in the delocalised ring of pi electrons
therefore they are more reactive towards electrophiles
direct substitutions to positions 2 and 4 on benzene ring
which group are electron donating on benzene? - Ans>>NO2
decrease the electron density in the delocalised ring of pi electrons
therefore they are less reactive towards electrophiles
direct substitutions to position 3 on benzene ring
how does an amine act as a base? - Ans>>can accept H+ ions using lone pair on N
(coordinate bond) forming an ammonium salt
how is a primary aliphatic amine made?
and why does the reagent need to be in excess - Ans>>from reacting haloalkane
with excess ammonia in ethanol.
excess ammonia avoids further substitution to secondary and tertiary amines.
how is a secondary and primary amine made? - Ans>>from reacting excess
haloalkane with ammonia and ethanol
the lone pair on the N of the primary amine will attack another haloalkane
how is an aromatic amine made? - Ans>>by reducing nitrobenzene using tin and
concentrated HCl
how are amines made from nitriles/hydroxynitriles? - Ans>>by reducing nitriles
using H2/Ni catalust
how to test for an alkene? - Ans>>react with Br2 and bromine is decolourised
What two types of bond are within an alkene? - Ans>>sigma and pi
sigma bond - Ans>>the direct overlapping of two orbitals
pi bond - Ans>>the sideways overlap of p orbitals
C=C how many pi bonds and sigma bonds are in this - Ans>>one sigma two pi
bonds
what two types of isomers are found in alkenes - Ans>>cis/trans and E/Z
Difference between E/Z isomers and Cis/trans isomers - Ans>>E/Z compares
relative position based in priority groups (IP rules) look at the atomic number of the
first bonded element
Cis/Trans compares the relative positions of identical groups
major and minor products in alkenes - Ans>>the major product forms the most
stable carbocation intermediate during alkene reactions
tertiary>secondary>primary
what type of polymer do alkenes produce? - Ans>>addition polymers
synthesis of an organic liquid - Ans>>once reaction is complete into a separating
funnel. Neutralise any excess acid using sodium carbonate (stops bubbling when all
gone)
Allow 2 layers to settle
Use density into to establish layers. If density into not given, add water to establish
aqueous layer.
(aqueous layer get bigger)
Density of water is 1 anything greater is more dense.
collect the organic layer
add a drying agent to remove small traces of water left in the organic layer (e.g..
anhydrous CaCl2)
If the question tells you the boiling point of the organic liquid say distil dried product
and collect fraction that comes over the boiling point.
3 ways to determine purity of products - Ans>>1. boiling point should match known
data, boils over a narrow range
,or
2. Run TLC, measure Rf value, compare to known data values/Run TLC and compare
to chromatogram of pure sample
or
3. Run NMR/IR/Mass spectrum, compare to spectral database of pure compounds.
How to purify by recrystallisation? - Ans>>-dissolve in a minimum volume of hot
solvent
-cool in ice to recrystallise (impurities stay in solution)
-filter using Büchner flask/reduced pressure filtration
-wash with cold solvent
-dry
Does reflux have an open or closed system? - Ans>>open
overall equation for ozone depletion - Ans>>O3 + O -> 2O2
rate of formation of ozone = - Ans>>rate of breakdown of ozone by UV light =
what type of compound breaks down the ozone layer? - Ans>>chlorofluorocarbons
Initiation reaction of CCl3F
what is the mechanism, equation and why the radicals formed - Ans>>homolytic
bond fission
Cl. + CCl2F.
C-Cl bond broken as its weaker than C-F
Evidence for the structure of delocalised benzene against the kekule structure -
Ans>>-Bond lengths of benzene are the same
-enthalpy of hydrogenation less exothermic than expected
-does not undergo addition reaction
why does benzene need a halogen carrier to undergo electrophilic subsitution? -
Ans>>it is not electron dense enough to polarize the molecule into an electrophile
electrophile - Ans>>electron pair acceptor
what is the catalyst for halogenation of benzene? - Ans>>AlX3
what is the catalyst for nitration of benzene? - Ans>>sulfuric acid
How can you test for a phenol? - Ans>>weak acid that reacts with NaOH but too
weak to react with Na2CO3 so no bubbles of CO2
, why don't you need a catalyst for the halogenation and nitration of phenol? -
Ans>>The lone pair on the oxygen molecule in the hydroxyl group donates its pair
of electrons into the delocalised pi ring. Increases the electron density of the phenol
molecule which allows phenol to polarise HNO3 and X2 molecules to produce an
electrophile
what is the colour change when phenol is halogenated with Bromine molecule? -
Ans>>Br2 is decolourised and a white ppt is formed.
Describe the reactivity if benzene Vs alkenes - Ans>>Benzene, the Pi electrons are
decolourised Pi electron density is low compared to alkene. Benzene is unable to
polarize electrophiles so can't attract them strongly. In C=C of alkenes the Pi
electrons are localised. Pi electron density is high (compared to benzene) able to
polarize electrophiles so attracts them strongly.
which groups are electron donating on benzene? - Ans>>OH and NH2
increase the electron density in the delocalised ring of pi electrons
therefore they are more reactive towards electrophiles
direct substitutions to positions 2 and 4 on benzene ring
which group are electron donating on benzene? - Ans>>NO2
decrease the electron density in the delocalised ring of pi electrons
therefore they are less reactive towards electrophiles
direct substitutions to position 3 on benzene ring
how does an amine act as a base? - Ans>>can accept H+ ions using lone pair on N
(coordinate bond) forming an ammonium salt
how is a primary aliphatic amine made?
and why does the reagent need to be in excess - Ans>>from reacting haloalkane
with excess ammonia in ethanol.
excess ammonia avoids further substitution to secondary and tertiary amines.
how is a secondary and primary amine made? - Ans>>from reacting excess
haloalkane with ammonia and ethanol
the lone pair on the N of the primary amine will attack another haloalkane
how is an aromatic amine made? - Ans>>by reducing nitrobenzene using tin and
concentrated HCl
how are amines made from nitriles/hydroxynitriles? - Ans>>by reducing nitriles
using H2/Ni catalust
how to test for an alkene? - Ans>>react with Br2 and bromine is decolourised
