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Date	November 2017	Marks available	1	Reference code	17N.2.hl.TZ0.8
Level	HL	Paper	2	Time zone	TZ0
Command term	Deduce	Question number	8	Adapted from	N/A

Question

The reactivity of organic compounds depends on the nature and positions of their functional groups.

The structural formulas of two organic compounds are shown below.

Deduce, giving a reason, which of the two compounds can show optical activity.

[1]

a.iv.

Draw three-dimensional representations of the two enantiomers.

[1]

a.v.

State the reagents used in the nitration of benzene.

[1]

c.

State an equation for the formation of NO₂⁺.

[1]

d.

Explain the mechanism of the reaction between 2-bromo-2-methylpropane, (CH₃)₃CBr, and aqueous sodium hydroxide, NaOH (aq), using curly arrows to represent the movement of electron pairs.

[4]

e.

Markscheme

A AND it has a chiral centre/asymmetric carbon atom/carbon with 4 different substituents

a.iv.

Accept structures without tapered bonds.

a.v.

concentrated HNO₃ AND concentrated H₂SO₄

“concentrated” must occur at least once (with either acid).

c.

HNO₃ + 2H₂SO₄ $\rightleftharpoons$ H₃O⁺ + NO₂⁺+ 2HSO₄^–

Accept: HNO₃ + 2H₂SO₄ $\rightleftharpoons$ NO₂⁺+ HSO₄^–+ H₂O.

Accept: HNO₃ + 2H₂SO₄ $\rightleftharpoons$ H₂NO₃⁺ + HSO₄^–.

Accept single arrow instead of equilibrium sign.

Accept equivalent two step reactions in which sulfuric acid first behaves as strong acid and protonates nitric acid, before behaving as dehydrating agent removing water from it.

d.

curly arrow showing Br^– leaving

representation of tertiary carbocation

curly arrow going from lone pair/negative charge on O in ^–OH to C⁺

formation of (CH₃)₃COH AND Br^–

Do not accept curly arrow originating from C of C–Br bond.

Do not accept arrow originating on H in ^–OH.

Accept Br^– anywhere on product side in the reaction scheme.

Award [2 max] for an S_N2 type mechanism.

e.

Examiners report

[N/A]

a.iv.

[N/A]

a.v.

[N/A]

c.

[N/A]

d.

[N/A]

e.

Syllabus sections

Additional higher level (AHL) » Topic 20: Organic chemistry » 20.3 Stereoisomerism

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17M.2.hl.TZ2.7d:
Below are two isomers, A and B, with the molecular formula C₄H₉Br.

Explain the mechanism of the nucleophilic substitution reaction with NaOH(aq) for the isomer that reacts almost exclusively by an S_N2 mechanism using curly arrows to represent the movement of electron pairs.
18M.1.hl.TZ2.37: Which isomers exist as non-superimposable mirror images? A. cis-trans isomers B. ...
16N.2.hl.TZ0.6b: When one enantiomer undergoes substitution by alkaline hydrolysis approximately 75 % of the...
17M.3.hl.TZ1.28a:
Describe what happens to plane-polarized light when it passes through a solution of an optically active compound.
19M.1.hl.TZ2.36: Which compound exists as two configurational isomers? A. CBr2=CH2 B. CH2=CHBr C....
18M.1.hl.TZ1.35: What is name of this compound applying IUPAC rules? A. E...
18M.3.hl.TZ2.8e:
Sketch the wedge and dash (3-D) representations of alanine enantiomers.
19N.1.hl.TZ0.38:
Which can show optical activity?

A. CHBrCHCl

B. CH₃CH₂CHBrCH₂CH₃

C. (CH₃)₂CBrCl

D. CH₃CH₂CH(CH₃)Br
22M.2.hl.TZ2.8d(i):
Draw the full structural formula of (Z)-but-2-ene.
18N.1.hl.TZ0.37:
How many chiral carbon atoms are present in one molecule of (CH₃)₂CHCHClCHBrCH₃?

A. 0

B. 1

C. 2

D. 3
16N.2.hl.TZ0.6a: Draw the three-dimensional shape of each enantiomer of this isomer showing their spatial...
18N.2.hl.TZ0.8b.ii: State, giving a reason, whether methyloxirane can form cis-trans isomers.
19M.2.hl.TZ1.1e:
The organic product is not optically active. Discuss whether or not the organic product is a racemic mixture.
17M.3.hl.TZ1.28b:
A mixture of enantiomers shows optical rotation.

Suggest a conclusion you can draw from this data.
17M.1.hl.TZ2.35: Which pair of isomers always shows optical activity? A. Cis-trans B. ...
17M.3.hl.TZ1.17:
Vision is dependent on retinol (vitamin A) present in retina cells. Retinol is oxidized to the photosensitive chemical 11-cis-retinal and isomerizes to 11-trans-retinal on absorption of light.

Outline how the formation of 11-trans-retinal results in the generation of nerve signals to the brain.
17N.2.hl.TZ0.8a.v: Draw three-dimensional representations of the two enantiomers.
19M.1.hl.TZ1.37: Which compound can exist as cis- and trans-isomers?
17N.1.hl.TZ0.37: What is the number of optical isomers of isoleucine? A. 0 B. 2 C. 4 D. 8
19M.3.hl.TZ1.5a:
Label with an asterisk, *, the chiral carbon atom.
17M.1.hl.TZ1.37: Which molecule is chiral? A. 2-chlorobutane B. 2,2-dichloropentane C. ...
16N.1.hl.TZ0.37: Which statement is correct for a pair of enantiomers under the same conditions? A. A...
19N.3.hl.TZ0.26a: State the feature of Taxol that is a major challenge in its synthesis. Use section 37 of the...
18M.1.hl.TZ1.36:
Which molecule contains a chiral carbon?

A. CH₃CH₂CHBrCH₂CH₃

B. CH₃CH₂CHBrCH₃

C. CH₂BrCH(CH₃)CH₂Br

D. CH₃CH₂CH₂CH₂CH₂Br
21M.2.hl.TZ2.4h(ii): Outline how two enantiomers can be distinguished using a polarimeter.
18M.2.hl.TZ2.9b.iv:
Suggest, giving a reason, the percentage of each isomer from the S_N1 reaction.
19M.2.hl.TZ2.6d(ii):
The minor product, C₆H₅–CH₂–CH₂Br, can exist in different conformational forms (isomers).

Outline what this means.
19M.2.hl.TZ2.6d(i):
Outline why the major product, C₆H₅–CHBr–CH₃, can exist in two forms and state the relationship between these forms.

Two forms:

Relationship:
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21M.1.hl.TZ2.36:
Which compound rotates the plane of plane-polarized light?

A. CH₃C(CH₃)ClCH₃

B. CH₃CH₂CHClCH₃

C. CH₃C(Cl)₂CH₃

D. CH₃CClBrCH₃
20N.1.hl.TZ0.37:
Which molecule has an enantiomer?

A.   ${CH}_{3} {CH}_{2} CH (OH) {CH}_{2} {CH}_{3}$

B.   ${CH}_{2} (OH) {CH}_{2} {CH}_{2} CH = {CH}_{2}$

C.   ${CH}_{3} {CH}_{2} {CH}_{2} CH = CHBr$

D.   ${CH}_{3} {CHBrCH}_{2} {CH}_{2} {CH}_{3}$
21M.2.hl.TZ2.4h(i): Draw the stereoisomers of butan-2-ol using wedge-dash type representations.
22M.1.hl.TZ1.37: What are the E/Z designations of these stereoisomers?
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Additional higher level (AHL) » Topic 20: Organic chemistry

Additional higher level (AHL)