The questions below are all on calorimetry. Each page has only one question on it, and the mark scheme for each question is on the page that immediately follows. Some parts of some of the questions will come from other topics. A printable copy of the questions can be found here.
Question 1
Which alkene shows E–Z isomerism?
(Total 1 mark)
Question 2
Which has E–Z isomers?
(Total 1 mark)
Question 3
Which statement is not correct about CH2═C(CH3)CH2Br?
(Total 1 mark)
Question 4
What is the empirical formula of 4-hydroxypent-2-ene?
(Total 1 mark)
Question 5
Z-Retinal, shown in the diagram, is a component in vitamin A.
Which of the double bonds, labelled A, B, C or D, is responsible for the letter Z in the name?
(Total 1 mark)
Question 6
Which statement about E-1,2-dichloroethene is correct?
(Total 1 mark)
Question 7
Which statement about ethene is correct?
(Total 1 mark)
Q1.
B
4-methylpent-2-ene
[1]
Q2.
A
[1]
Q3.
A
It displays E-Z isomerism
[1]
Q4.
B
[1]
Q5.
C
[1]
Q6.
B
[1]
Q7.
C
[1]
Question 8
The alkene (E)-but-2-enenitrile is used to make acrylic plastics.
The structure of (E)-but-2-enenitrile is
(a) (i) Draw the structure of (Z)-but-2-enenitrile.
(1)
(ii) Identify the feature of the double bond in the E and Z isomers that causes them to be stereoisomers.
(1)
(b) Draw the repeating unit of the polyalkene formed by addition polymerisation of (E)-but-2-enenitrile.
(1)
(c) Consider the infrared spectrum of (E)-but-2-enenitrile.
Identify two features of the infrared spectrum that support the fact that this is the infrared spectrum for but-2-enenitrile.
(2)
(Total 5 marks)
Q8.
(a) (i) Structure of (Z)-but-2-enenitrile with or without either or both of the CH3 and the CN groups displayed
Penalise C−NC
Do not penalise C−H3C
Ignore bond angles.
1
(ii) Restricted rotation / no (free) rotation about the double bond / about the C=C OR does not rotate (about the double bond)
Must use the word rotate / rotation.
1
(b) Repeating unit of polyalkene
All the bonds relevant to the unit must be drawn out including those on either side of the unit. There is no need to expand either the CH3 or the CN
Penalise C−NC
Penalise “sticks”.
Ignore brackets.
Penalise “n”
1
(c) Feature 1
Absorption / peak in the range 2220 to 2260 cm−1 or specified value in this range or marked correctly on spectrum
and
(characteristic absorption / peak for) C≡N / CN group / nitrile / cyanide group
Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption.
Allow a peak at 2200 cm−1 to 2220 cm−1 in this case.
Feature 2
Absorption / peak in the range 1620 to 1680 cm−1 or specified value in this range or marked correctly on spectrum
and
(characteristic absorption / peak for) C=C group / alkene / carbon-carbon double bond
Ignore reference to other absorptions eg C-H
Either order.
2
[5]
Q9.
Alkenes are useful intermediates in the synthesis of organic compounds.
(a) (i) Complete the elimination mechanism by drawing appropriate curly arrows.
(3)
(ii) Draw structures for the E and Z stereoisomers of hex-3-ene.
E isomer of hex-3-ene Z isomer of hex-3-ene
(2)
(iii) State the meaning of the term stereoisomers.
(2)
(b) The equation for the first reaction in the conversion of hex-3-ene into hexan-3-ol is shown below.
CH3CH2CH=CHCH2CH3 + H2SO4 CH3CH2CH2CH(OSO2OH)CH2CH3
Outline a mechanism for this reaction.
(4)
(Total 11 marks)
(a) (i)
Penalise one mark from their total if half-headed arrows are used
Penalise M3 for formal charge on C of the C-Br or incorrect partial charges on C-Br
Ignore other partial charges
M1 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to the correct H atom
Penalise once only in any part of the mechanism for a line and two dots to show a bond.
M2 must show an arrow from the correct C–H bond to the correct C–C bond.
Only award if an arrow is shown attacking the H atom of the correct C–H
bond in M1
M3 is independent but CE=0 if nucleophilic substitution
N.B these are double-headed arrows
3
(ii)
Award 1 mark if both correct stereoisomers but in the wrong places
Accept no other alkenes.
Be reasonably lenient on the bonds to ethyl (or to CH2CH3) since the question is about E and Z positions but penalise once only if connection is clearly to the CH3 of CH2CH3
Accept linear structures
2
(iii) M1 (Compounds / molecules with) the same structural formula
Penalise M1 if “same structure”
M2 with atoms/bonds/groups arranged differently in space
Ignore references to “same molecular formula” or “same empirical formula” or any reference to “displayed formula”
OR
atoms/bonds/groups that have different spatial arrangements / different orientation.
Mark independently
2
(b)
M1must show an arrow from the double bond towards the H atom of the H – O bond
OR HO on a compound with molecular formula for H2SO4
M1 could be to an H+ ion and M2 an independent O – H bond break on a compound with molecular formula for H2SO4
M1 Ignore partial negative charge on the double bond.
M2 must show the breaking of the O – H bond.
M2 Penalise partial charges on O – H bond if wrong way and penalise formal charges
In M2 do not penalise incorrect structures for H2SO4
M3 is for the structure of the carbocation.
M4 must show an arrow from the lone pair of electrons on the correct oxygen of the negatively charged ion towards a correct (positively charged) carbon atom.
M4 NOT HSO4–
For M4, credit as shown or –:OSO3H ONLY with the negative charge anywhere on this ion
OR correctly drawn out with the negative charge placed correctly on oxygen
Penalise once only in any part of the mechanism for a line and two dots to show a bond
NB The arrows here are double-headed
Max 3 of any 4 marks for wrong organic reactant or wrong organic product (if shown)
Accept the correct use of “sticks”
4
[11]
Question 10
It is possible to convert but-1-ene into its structural isomer but-2-ene.
(a) State the type of structural isomerism shown by but-1-ene and but-2-ene.
(1)
(b) The first stage in this conversion involves the reaction of hydrogen bromide with but-1-ene.
Outline a mechanism for this reaction.
(4)
(c) The second stage is to convert 2-bromobutane into but-2-ene.
Outline a mechanism for this reaction.
(3)
(Total 8 marks)
Q10.
(a) Position(al) (isomerism)
1
(b)
Penalise one mark from their total if half-headed arrows are used
M1 must show an arrow from the double bond towards the H atom of the H–Br
molecule
M1 Ignore partial negative charge on the double bond.
M2 must show the breaking of the H–Br bond.
M2 Penalise partial charges on H–Br bond if wrong way and penalise formal charges
M3 is for the structure of the secondary carbocation.
Penalise M3 if there is a bond drawn to the positive charge
M4 must show an arrow from the lone pair of electrons on the negatively charged
bromide ion towards the positively charged carbon atom of either a primary or
secondary carbocation.
Penalise once only in any part of the mechanism for a line and two dots to show a bond
Maximum any 3 of 4 marks for wrong reactant or primary carbocation.
If Br2 is used, maximum 2 marks for their mechanism
Do not penalise the use of “sticks”
NB The arrows here are double-headed
4
(c)
Penalise one mark from their total if half-headed arrows are used
M1 must show an arrow from the lone pair on oxygen of a negatively charged
hydroxide ion to a correct H atom
Penalise M1 if covalent KOH
M2 must show an arrow from a C–H bond adjacent to the C–Br bond towards
the appropriate C–C bond. Only award if an arrow is shown attacking the
H atom of an adjacent C–H (in M1)
M3 is independent provided it is from their original molecule.
Penalise M3 for formal charge on C of the C–Br or incorrect partial charges on C–Br
Penalise M3 if an extra arrow is drawn from the Br of the C–Br bond to, for example, K+
Ignore other partial charges
Penalise once only in any part of the mechanism for a line and two dots to show a bond.
Maximum any 2 of 3 marks for wrong reactant or wrong product
(if shown) or a mechanism that leads to but-1-ene
Accept the correct use of “sticks” for the molecule except for the C–H being attacked
Award full marks for an E1 mechanism in which M2 is on the correct carbocation.
NB The arrows here are double-headed
3
[8]
Question 12
The table below shows the structures of three isomers with the molecular formula C5H10O
(a) Complete the table by naming Isomer 3.
(1)
(b) State the type of structural isomerism shown by these three isomers.
(1)
(c) The compound (Z)-pent-3-en-2-ol is a stereoisomer of (E)-pent-3-en-2-ol.
(i) Draw the structure of (Z)-pent-3-en-2-ol.
(1)
(ii) Identify the feature of the double bond in (E)-pent-3-en-2-ol and that in
(Z)-pent-3-en-2-ol that causes these two compounds to be stereoisomers.
(1)
(d) A chemical test can be used to distinguish between separate samples of Isomer 2 and Isomer 3.
Identify a suitable reagent for the test.
State what you would observe with Isomer 2 and with Isomer 3.
(3)
(e) The following is the infrared spectrum of one of the isomers 1, 2 or 3.
(i) Deduce which of the isomers (1, 2 or 3) would give this infrared spectrum. You may find it helpful to refer to Table 1 on the Data Sheet.
(1)
(ii) Identify two features of the infrared spectrum that support your deduction.
In each case, identify the functional group responsible.
(2)
(Total 10 marks)
Q12.
(a) Pentan-2-one
ONLY but ignore absence of hyphens
1
(b) Functional group (isomerism)
Both words needed
1
(c) (i)
Award credit provided it is obvious that the candidate is drawing the Z / cis isomer
The group needs to be CHOHCH3 but do not penalise poor C–C bonds or absence of brackets around OH
Trigonal planar structure not essential
1
(ii) Restricted rotation (about the C=C)
OR
No (free) rotation (about the C=C)
1
If M1 is blank CE = 0, for the clip
Check the partial reagents listed and if M1 has a totally incorrect reagent, CE = 0 for the clip
Allow the following alternatives
M1 (acidified) potassium dichromate(VI) (solution); mark on from incomplete formulae or incorrect oxidation state
M2 (turns) green
M3 (stays) orange / no (observed) change / no reaction
OR
M1 (acidified) potassium manganate(VII) (solution);
mark on from incomplete formulae or incorrect oxidation state
M2 (turns) colourless
M3 (stays) purple / no (observed) change / no reaction
In all cases for M3
Ignore “nothing (happens)”
Ignore “no observation”
3
(e) (i) Spectrum is for Isomer 1
or named or correctly identified
The explanation marks in (e)(ii) depend on correctly identifying Isomer 1.
The identification should be unambiguous but candidates should not be penalised for an imperfect or incomplete name. They may say “the alcohol” or the “alkene” or the “E isomer”
1
(ii) If Isomer 1 is correctly identified, award any two from
• (Strong / broad) absorption / peak in the range
3230 to 3550 cm–1 or specified value in this range
or marked correctly on spectrum
and
(characteristic absorption / peak for) OH group /alcohol group
• No absorption / peak in range 1680 to 1750 cm–1 or
absence marked correctly on spectrum
and
(No absorption / peak for a) C=O group / carbonylgroup / carbon-oxygen double bond
• Absorption / peak in the range 1620 to 1680 cm–1
or specified value in this range or marked correctly
on spectrum
and
(characteristic absorption / peak for) C=C group
/ alkene / carbon-carbon double bond
If 6(e)(i) is incorrect or blank, CE=0
Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption.
Ignore reference to other absorptions e.g. C-H, C-O
2
[10]
Q13.
Organic reaction mechanisms help chemists to understand how the reactions of organic compounds occur.
The following conversions illustrate a number of different types of reaction mechanism.
(a) When 2-bromopentane reacts with ethanolic KOH, two structurally isomeric alkenes are formed.
(i) Name and outline a mechanism for the conversion of 2-bromopentane into
pent-2-ene as shown below.
(4)
(ii) Draw the structure of the other structurally isomeric alkene produced when 2-bromopentane reacts with ethanolic KOH.
(1)
(b) Name and outline a mechanism for the following conversion.
(5)
(c) Name and outline a mechanism for the following conversion.
(5)
(Total 15 marks)
Q13.
(a) (i) M1 Elimination
M2 must show an arrow from the lone pair on the oxygen
of a negatively charged hydroxide ion to a correct H atom
M3 must show an arrow from a C-H bond adjacent to
the C-Br bond towards the appropriate C-C bond.
Only award if a reasonable attempt has been made
at the attack on the H atom of the appropriate adjacent C-H
M4 is independent provided it is from their original molecule
Award full marks for an E1 mechanism in which M3 is on the correct carbocation.
N.B. These are double-headed arrows
For M1, accept “Base elimination” but no other prefix.
Penalise M2 if covalent KOH
Penalise M4 for formal charge on C of C-Br or incorrect partial charges on C-Br
Ignore other partial charges
Penalise once only in any part of the mechanism for a line and two dots to show a bond.
Max any 2 of 3 marks for the mechanism for wrong reactant (or wrong product if shown).
Accept the correct use of “sticks” for the molecule except for the C-H being attacked
4
(ii) Structure for pent-1-ene
CH3CH2CH2CH=CH2
Penalise C3H7
Accept correct “sticks”
1
(b) M1 Electrophilic addition
M2 must show an arrow from the double bond towards the Br atom of the Br-Br molecule
M3 must show the breaking of the Br-Br bond.
M4 is for the structure of the tertiary carbocation with Br on the correct carbon atom.
M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged carbon atom.
N.B. These are double-headed arrows
For M1, both words required.
For the mechanism
M2 Ignore partial negative charge on the double bond.
M3 Penalise partial charges on Br-Br bond if wrong way and penalise formal charges
Penalise once only in any part of the mechanism for a line and two dots to show a bond
Max any 3 of 4 marks for the mechanism for
wrong organic reactant or wrong organic product (if shown) or primary carbocation.
If HBr is used, max 2 marks for their mechanism
Accept the correct use of “sticks”
5
(c) M1 Nucleophilic substitution
M2 must show an arrow from the lone pair of electrons on the nitrogen
atom of an ammonia molecule to the C atom.
M3 must show the movement of a pair of electrons from the C-Br bond
to the Br atom. M3 is independent provided it is from their original molecule
M4 is for the structure of the alkylammonium ion, which could be a
condensed formula. A positive charge must be shown on/or close to,
the N atom.
M5 is for an arrow from the N-H bond to the N atom.
Award full marks for an SN1 mechanism in which M2 is the attack
of the ammonia on the intermediate carbocation.
N.B. These are double-headed arrows
For M1, both words required.
Penalise M2 if NH3 is negatively charged.
Penalise M3 for formal charge on C or incorrect partial charges
The second mole of ammonia is not essential for M5; therefore ignore any species here.
Penalise once only for a line and two dots to show a bond.
Max any 3 of 4 marks for the mechanism for wrong organic reactant (or wrong organic product if shown)
Accept the correct use of “sticks”
5
[15]