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 14
The alkene (Z)-3-methylpent-2-ene reacts with hydrogen bromide as shown below.
(a) (i) Name the major product P.
(1)
(ii) Name the mechanism for these reactions.
(1)
(iii) Draw the displayed formula for the minor product Q and state the type of structural isomerism shown by P and Q.
(2)
(iv) Draw the structure of the (E)-stereoisomer of 3-methylpent-2-ene.
(1)
(b) The infrared spectra of two compounds R and S are shown below. R and S have the molecular formula C6H12 and are structural isomers of 3-methylpent-2-ene. R is an unsaturated hydrocarbon and S is a saturated hydrocarbon.
Spectrum 1
Spectrum 2
(i) Identify the infrared Spectrum 1 or 2 that represents compound R.
Use information from the infrared spectra to give one reason for your answer.
You may find it helpful to refer to Table 1 on the Data Sheet.
(2)
(ii) State the type of structural isomerism shown by R and S.
(1)
(iii) Name one possible compound which could be S.
(1)
(Total 9 marks)
Q14.
(a) (i) 3-bromo-3-methylpentane ONLY
Must be correct spelling but ignore hyphens and commas
1
(ii) Electrophilic addition (reaction)
Both words needed
Accept phonetic spelling
1
(iii) M1 Displayed formula of 2-bromo-3-methylpentane
All the bonds must be drawn out but ignore bond angles
M2 Position(al) (isomerism)
Do not forget to award this mark
2
(iv) Structure of (E)-3-methylpent-2-ene
The arrangement of groups around the double bond must be clear with the ethyl group attached in the correct order. Ignore bond angles.
Accept C2H5 for ethyl
Be lenient on C ─ C bonds. The main issue here is whether they have drawn an (E) isomer.
Accept “sticks” for C ─ H bonds and correct skeletal formula
1
(b) (i) M1 R is represented by Spectrum 2
M2 Spectrum 2 shows an infrared absorption/spike/dip/
trough/peak with any value(s)/range within the range 1620 to
1680 (cm–1) OR this range quoted/identified and this
is due to C=C
OR this information could be a correctly labelled absorption
on the spectrum
OR Spectrum 1 does not have an infrared absorption in range
1620 to 1680 (cm–1) and does not contain C=C.
Award M1 if it is obvious that they are referring to the second spectrum (or the bottom one)
M2 depends on a correct M1
Ignore other correctly labelled peaks
Ignore reference to “double bond” or “alkene”
2
(ii) Functional group (isomerism)
1
(iii) Cyclohexane
OR
Methylcyclopentane etc.
Named correctly
Ignore structures and ignore numbers on the methyl group of methylcyclopentane
1
[9]
Question 15
The reaction of bromine with an alkene is used in a test to show that the alkene is unsaturated.
(a) State what is meant by the term unsaturated as applied to an alkene.
(1)
(b) Name and outline a mechanism for the reaction of bromine with but-2-ene.
(5)
(c) But-2-ene can exist as a pair of stereoisomers.
(i) State what is meant by the term stereoisomers.
(2)
(ii) Draw the structure of (E)-but-2-ene.
(1)
(Total 9 marks)
Q15.
(a) Contains a C=C OR a double bond
1
(b) Electrophilic addition
Both words needed
1
Mechanism:
Ignore partial negative charge on the double bond.
M2 Penalise partial charges on bromine 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.
M1 Must show an arrow from the double bond towards one
of the Br atoms on a Br-Br molecule.
Deduct 1 mark for sticks.
M2 Must show the breaking of the Br-Br bond.
M3 Is for the structure of the secondary carbocation with Br substituent.
M4 Must show an arrow from the lone pair of electrons on a
negatively charged bromide ion towards the positively
charged carbon atom.
Deduct 1 mark for wrong reactant, but mark consequentially.
If HBr, mark the mechanism consequentially and deduct one mark
If but-1-ene, mark the mechanism consequentially and deduct one mark.
If both HBr and but-1-ene, mark the mechanism consequentially and deduct ONLY one mark.
4
(c) (i) M1 Compounds with the same structural formula
Penalise M1 if “same structure”
Ignore references to “same molecular formula” or “same empirical formula”
1
M2 With atoms/bonds/groups arranged differently in space
OR
atoms/bonds/groups have different spatial
arrangements/ different orientation.
Mark independently.
1
(ii)
Award credit provided it is obvious that the candidate is drawing the trans isomer.
Do not penalise poor C–C bonds
Trigonal planar structure not essential
1
[9]
Question 16
(a) Compounds with double bonds between carbon atoms can exhibit geometrical isomerism.
(i) Draw structures for the two geometrical isomers of 1,2-dichloroethene.
(ii) What feature of the double bond prevents isomer 1 from changing into isomer 2?
(3)
(b) When 2-chloropropane reacts with sodium hydroxide, two different reactions occur.
Each reaction produces a different organic product.
(i) Outline a mechanism for Reaction 1 and state the role of the hydroxide ion in this reaction.
(ii) Outline a mechanism for Reaction 2 and state the role of the hydroxide ion in this reaction.
(7)
(Total 10 marks)
Question 17
The correct systematic name for 
is
A 2-ethyl-3,4-dimethylpent-2-ene
B 4-ethyl-2,3-dimethylpent-3-ene
C 2,3,4-trirnethylhex-3-ene
D 3,4,5-trimethylhex-3-ene
(Total 1 mark)
Q16.
(a) (i)
(ii) restricted rotation OR no rotation OR cannot rotate (1)
3
(b) (i) Mechanism:
M1 and M2 independent
Curly arrows must be from a bond or a lone pair
Do not penalise sticks
Penalise M1 if precedes (penalise this once)
Penalise incorrect δ+ δ– for M2
Penalise + on C atom for M2
Only allow M1 for incorrect haloalkane
Role of the hydroxide ion: nucleophile (1)
electron pair donor
lone pair donor
NOT nucleophilic substitution
(ii) Mechanism:
Only allow M1 and M2 for incorrect haloalkane unless RE on (i)
+ charge on H on molecule, penalise M1
M3 independent
M2 must be to correct C–C
M1 must be correct H atom
Credit M1 and M2 via carbocation mechanism
No marks after any attack of C+ by OH–
Role of the hydroxide ion: base (1)
proton acceptor
accepts H+
7
[10]
Q17.
C
[1]