Download chirality - KS5Chemistry

1.
Adrenalin is a hormone which raises blood pressure, increases the depth of breathing and delays
fatigue in muscles, thus allowing people to show great strength under stress.
Benzedrine is a pharmaceutical which stimulates the central nervous system in a similar manner
to adrenalin.
HO
CH2
CH(CH 3 )
NH 2
HO
Benzedrine
(a)
(i)
H
CH(OH)
CH 2
N
CH 3
Adrenalin
On the structure for benzedrine mark with a (*) any asymmetric carbon atom that
causes chirality.
(1)
(ii)
Suggest why adrenalin is more soluble in water than is benzedrine.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(b)
Give the structural formulae of the organic products obtained when benzedrine reacts
with:
(i)
an aqueous acid such as dilute hydrochloric acid;
(1)
(ii)
ethanoyl chloride in the absence of a catalyst;
(1)
(iii)
excess ethanoyl chloride in the presence of the catalyst anhydrous aluminium
chloride.
(2)
Maltby Academy
1
(d)
It is possible to eliminate a molecule of water from adrenalin which for the purpose of
this question may be represented as R–CH(OH)–CH2–NH–CH3. Draw the structural
formulae of the two stereoisomers produced.
(2)
(e)
The mass spectra of both benzedrine and adrenalin have a peak at a mass/charge ratio of
44. Draw the structure of the species which give these peaks.
(i)
in benzedrine;
(1)
(ii)
in adrenalin.
(1)
(Total 11 marks)
2.
Alanine, 2-aminopropanoic acid, is the simplest chiral amino acid found in nature and is
optically active.
H
H2N
C
CH3
Maltby Academy
O
C
O
H
2
(a)
(i)
Explain the meaning of the term chiral.
.....................................................................................................................................
.....................................................................................................................................
(1)
(ii)
How is optical activity detected experimentally?
.....................................................................................................................................
.....................................................................................................................................
(2)
(iii)
If alanine is made from propanoic acid the product mixture does not show optical
activity. Explain why this is so.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(2)
(b)
Alanine reacts with both acids and bases. Give the structural formulae of the compounds
you would expect if alanine reacts with
hydrochloric acid
sodium hydroxide
(2)
Maltby Academy
3
(c)
Alanine has a high melting temperature of 300 °C, much higher than would be expected
for the structure given at the start of the question.
Draw the structure that is actually present in the solid, and explain why the melting
temperature is so high.
............................................................................................................................................
...........................................................................................................................................
............................................................................................................................................
(2)
(d)
Polyamides are made from a diacid dichloride and a diamine; they are condensation
polymers.
(i)
Explain the term condensation polymer.
.....................................................................................................................................
.....................................................................................................................................
(1)
(ii)
Suggest the structural formula of a diacid dichloride and a diamine that could be
reacted to form a polyamide.
(2)
Maltby Academy
4
(iii)
Draw sufficient of the polymer chain that would result from the reaction of the
compounds in (ii) to make the structure of the polymer clear.
(2)
(iv)
Alanine could be converted to CH3CH(NH2)COCl which on its own could
polymerise to a polyamide. Draw the structure of the polymer chain showing three
alanine repeating units and all the bonds in the amide links.
(2)
(Total 16 marks)
3.
A chemist has synthesised a compound W believed to be
Cl
HO
CH
CH
CH
O
C
OH
Maltby Academy
5
(a)
State and explain what you would see if W is reacted with:
(i)
sodium carbonate solution
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
bromine water.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(3)
(b)
W shows both types of stereoisomerism.
(i)
How many stereoisomers of W are there? Briefly explain your answer.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(ii)
Explain why W shows optical isomerism.
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
Maltby Academy
6
(c)
Describe how you would show that W contains chlorine.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(5)
(Total 14 marks)
4.
The optical isomers of alanine, CH3CH(COOH)NH2
A
have different melting points
B
rotate the plane of plane polarised light in opposite directions
C
react at different rates with ethanoyl chloride, CH3COCl
D
both occur naturally in protein molecules
(Total 1 mark)
5.
(a)
(b)
(i)
– *CH(CH3)–
(ii)
(the three) OH groups (1)
allow adrenalin to form more hydrogen bonds with water
(than does benzedrine) (1)
(i)
(1)
1
–
2
1
CH 2 CH(CH 3 )NH3 +(Cl )
Can use R in place of C6H5CH2CH(CH3)– in both (i) and (ii)
Maltby Academy
7
(ii)
1
CH2 CH(CH 3 )N
C
H
O
CH 3
(1)
O
(iii)
CH 3
CH 2 CH(CH 3 )
C
O
R
NHCH 3
C
(e)
C
CH 3
H
substitution(s) in ring at any position(s)
production of amide (1)
(d)
N
R
C
(1)
H
C
2
2
C
NHCH 3
H
H
H
(i)
(CH(CH3)–NH2)+
(1)
(ii)
(CH2–NH–CH3)+ / (CH(OH)CH2)+ (1)
max 1 for (e) if no charges shown
must show some structure in answers ie. C2H5N(0)
1
1
[11]
6.
(a)
(i)
(ii)
(iii)
(b)
(c)
It is non-superimposable on mirror image/ it has a single asymmetric
carbon atom
1
rotates the plane (of polarisation) (1)
of (plane–) polarised (monochromatic) light (1)
OR
Use a polarimeter (1)
rotates the plane (of polarisation) of the light (1)
2
product is an equimolar mixture/racemic mixture (1)
so rotations cancel (1)
2
– NH3 +Cl– on the amino group (1)
–COO– Na+ on the carboxyl group (1)
2
Zwifterion’s structure (1)
There is ionic attraction between adjacent zwitterions (1)
2
Maltby Academy
8
(d)
(i)
(polymer formed by) elimination/ removal of a small molecule/ water
(between two monomers)
1
(ii)
any CIOC***COCl (1) and H2N*CH2*NH2 (1)
2
(iii)
structure consequential on answer to (ii) showing amide link (1)
and extension of the chain (1)
2
(iv)
H
H H
H
N C
C N C
C N C
H CH3 O
C
CH3 O H CH 3 O
CONH drawn out (1)
Show 3 units (1)
2
[16]
7.
(a)
(i)
effervescence (1)
COOH present/acid/ acidic/contains H+ (1)
[if wrong gas is identified second mark is lost]
2
Accept bubbles, fizzing
Reject gas/CO2 evolved
Reject just „acid-base reaction‟
(ii)
Decolourises (1)
OR brown/orange/yellow to colourless
Reject “clear” used instead of “colourless”
compound contains C=C / unsaturated (1)
Accept alkene
Reject just „double bond‟
white precipitate so is a phenol (1)
3
Accept activated benzene ring/OH on benzene ring
Maltby Academy
9
(b)
(i)
Four (1)
(Two) cis/trans (or geometric), and (two) chiral/optical
isomers/ enantiomers (1)
OR
Two cis-trans/geometric isomers (1)
Two optical isomers/enantiomers (1)
OR
cis-trans/geometric isomers and
optical isomers/enantiomers (1 only)
2
Accept correct description of the idea of cis-trans or optical
isomerism without the name
Reject rotates plane of plane-polarised light
(ii)
Molecule has a chiral centre/chiral carbon/carbon with
four different groups (1)
having non-superimposable mirror images (1)
2
Reject asymmetric carbon atom/chiral molecule
(c)
QWC
NaOH (solution) (1)
Accept W identified as secondary halogenoalkane (1) so no
NaOH needed (1) for first two marks
acidify with /add excess HNO3 (1)
[If HCl is added here, only the NaOH mark can score]
Accept neutralise with nitric acid
Reject just “add HNO3”
add silver nitrate (solution) (1)
white precipitate (1)
soluble in dilute/aqueous ammonia (1)
Accept “dilute and concentrated ammonia”
Reject “concentrated ammonia” alone
If no NaOH max (4)
If HNO3 added only before NaOH, or no acid is added at all, then
can score 3rd, 4th and 5th marks
If order of addition is NaOH, AgNO3, HNO3 can score (5)
If no NaOH and no HNO3, can score last 3 marks
If any reagent other than silver nitrate, including ammoniacal
silver nitrate, is used only the 1st and 2nd marks can score
5
[14]
Maltby Academy
10
8.
B
[1]
Maltby Academy
11