OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2024: Question 17

8 marks · Medium difficulty · Structured Questions

Identify reagents, catalysts, and organic products for the elimination, oxidation, substitution, and esterification reactions of four structural isomers of butan-1-ol.

Practise this question

Question

A four-part question about the reactions of four structural isomers of C4H10O (alcohols). Part (a) asks for the reagent(s) and/or catalyst and organic product for the elimination reaction of CH3CH2CH2CH2OH. Part (b) asks for the oxidation reaction of CH3CH2CHOHCH3. Part (c) asks for the substitution reaction of (CH3)2CHCH2OH. Part (d) asks for the esterification reaction of (CH3)3COH. Each part has text lines for reagents/catalysts and a box labeled 'organic product' with values of 2 marks each.
Question text

17 This question is about reactions of alcohols.

There are 4 structural isomers of C4H10O that are alcohols:

CH3CH2CH2CH2OH

CH3CH2CHOHCH3

(CH3)2CHCH2OH

(CH3)3COH

Alcohols take part in many different types of reaction, including

• elimination

• oxidation

• substitution

• esterification.

For each type of reaction, choose appropriate reagent(s) and/or catalyst, and show the organic

product formed.

(a) Elimination reaction of CH3CH2CH2CH2OH

Reagent(s) and/or catalyst

organic product

[2]

(b) Oxidation reaction of CH3CH2CHOHCH3

Reagent(s) and/or catalyst

organic product

[2]

(c) Substitution reaction of (CH3)2CHCH2OH

Reagent(s) and/or catalyst

organic product

[2]

(d) Esterification reaction of (CH3)3COH

Reagent(s) and/or catalyst

organic product

[2]

Mark scheme

Show the mark scheme The mark scheme provides acceptable reagents and organic products for parts (a), (b), (c), and (d), including specific guidance notes on allowed/disallowed reagents and structural formulas for each reaction.

Question Answer Marks Guidance

17 (a) Reagent and/or catalyst: 2 DO NOT ALLOW other named acids e.g. HCl / hydrochloric

H SO OR H PO OR H+ OR acid (catalyst) acid as can be used for substitution reaction

24 3 4

DO NOT ALLOW other additional reagents e.g. H2O /

steam, H2 / hydrogen

ALLOW suitable non-specification alternatives e.g. Al2O3

OR Pumice stone

ALLOW names of reagents e.g. sulfuric or phosphoric acid,

if no formulae given

IGNORE concentration e.g. dilute/concentrated

IGNORE (aq) state symbol

IGNORE conditions e.g. temperature/pressure/reflux

Organic product: (mark independently) ALLOW any combination of skeletal OR structural OR

CH3CH2CHCH2 displayed formula as long as unambiguous

IGNORE names unless no structure is given then accept

but-1-ene

17 (b) Reagent and/or catalyst: 2 ALLOW Na2Cr2O7 for K2Cr2O7

K2Cr2O7 AND H2SO4 ALLOW names for reagents e.g. acidified dichromate, if no

OR Cr O 2–/H+ formulae given

IGNORE Roman numerals e.g. (VI), unless incorrect

IGNORE [O]

DO NOT ALLOW other named acids e.g. HCl / hydrochloric

acid

DO NOT ALLOW other additional reagents e.g. H2O, steam

ALLOW suitable non-specification alternative oxidising

agents e.g. KMnO /H+ OR CrO /H+ OR H CrO (chromic

43 2 4

acid)

IGNORE concentration e.g. dilute/concentrated

IGNORE conditions e.g. reflux/distillation

Organic product: (mark independently) ALLOW any combination of skeletal OR structural OR

CH3CH2COCH3 displayed formula as long as unambiguous

IGNORE names unless no structure is given then accept

butanone

17 (c) Mark organic product first: 2 ALLOW any combination of skeletal OR structural OR

displayed formula as long as unambiguous

(CH3)2CHCH2X IGNORE names unless no structure is given then accept 1-

where X is identified as Cl, Br, I halo-2-methylpropane, where halo is chloro, bromo or iodo

(ignore alphabetical order for prefixes)

Reagent and/or catalyst: For 2 marks, the reagent must be consistent with the

Reagent to match organic product product given e.g. (CH3)2CHCH2Cl then correct reagent is

NaCl / H2SO4

ALLOW 1 mark if correct reagents given but no or incorrect

NaX / KX / X- organic product shown

AND

H SO / H+ / acid ALLOW 1 mark if organic product is given with X i.e.

(CH ) CHCH X AND reagent is consistent e.g. NaX / H+ OR

32 2

Where X is identified as Cl, Br, I just states ‘halide with acid’

ALLOW HX where X is identified as Cl, Br, I

ALLOW names of reagents e.g. sodium bromide and

sulfuric acid, if no formulae given

DO NOT ALLOW other additional reagents e.g. AlCl3

ALLOW suitable non-specification alternative e.g.

PCl3, PCl5, (red) phosphorus AND bromine OR iodine,

SOCl2

IGNORE concentration e.g. dilute/concentrated

IGNORE conditions e.g. reflux/distillation

17 (d) Mark organic product first: 2 ALLOW any combination of skeletal OR structural OR

13 displayed formula as long as unambiguous

A correct ester of (CH3)3COH IGNORE additional byproducts e.g. H2O, HCl or carboxylic

e.g. (CH3)3COOCCH3 acid (from acid anhydride)

Reagent and/or catalyst: For 2 marks, the reagent must be consistent with the

Reagent to match ester shown product given e.g. (CH3)3COOCCH3 then correct reagent is

CH3COOH / H2SO4

suitable carboxylic acid AND acid / H+ catalyst, e.g.

CH3COOH/H2SO4 ALLOW 1 mark if correct reagents given but no or incorrect

OR organic product shown

suitable acyl chloride e.g. CH3COCl

OR ALLOW 1 mark if ester is given with an R group i.e.

suitable acid anhydride e.g. (CH3CO)2O (CH3)3COOCR AND reagent is consistent e.g. RCOOH OR

just states ‘carboxylic acid and acid’

ALLOW names of reagents e.g. ethanoic acid and sulfuric

acid.

DO NOT ALLOW other additional reagents e.g. Cr O 2-

IGNORE concentration e.g. dilute/concentrated

IGNORE conditions e.g. reflux/distillation

IGNORE use of acid catalyst with acyl chloride or acid

anhydride

How to answer it

Reactions of Alcohols Study Guide

📌 What this question tests

This question assesses your knowledge of core alcohol chemistry, specifically matching specific structural isomers of alcohols (C₄H₁₀O) with reagents, catalysts, and products for elimination, oxidation, substitution, and esterification reactions.

Part (a): Elimination Reaction of Butan-1-ol

CH₃CH₂CH₂CH₂OH

✅ Correct Answer

  • Reagent(s)/Catalyst: Concentrated H₂SO₄ OR Concentrated H₃PO₄ OR acid catalyst ( H⁺ ).
  • Organic Product: CH₃CH₂CH=CH₂ (but-1-ene).

💡 Key Knowledge

Dehydration of an alcohol is an elimination reaction. Heating a primary alcohol under reflux with a strong acid catalyst removes a water molecule from adjacent carbon atoms to form an alkene.

🧠 Exam Technique

Make sure to specify that the acid catalyst must be concentrated where applicable, though generic terms like "acid catalyst" or formulas like H₃PO₄ are also accepted by the mark scheme.

❌ Common Errors

Do NOT write hydrochloric acid ( HCl ), as this leads to a substitution reaction replacing the -OH with a chlorine atom instead of forming a double bond.

Allocated marks: 2 marks (1 for reagent/catalyst, 1 for organic product).

Part (b): Oxidation Reaction of Butan-2-ol

CH₃CH₂CHOHCH₃

✅ Correct Answer

  • Reagent(s)/Catalyst: Acidified potassium dichromate( VI ) — K₂Cr₂O₇ / H₂SO₄ or Cr₂O₇²⁻ / H⁺ .
  • Organic Product: CH₃CH₂COCH₃ (butanone).

💡 Key Knowledge

Secondary alcohols are oxidized by acidified dichromate to form ketones. The reaction involves the loss of hydrogen from the carbon bearing the hydroxyl group and from the -OH group itself.

🧠 Exam Technique

State both components of the oxidizing mixture ( K₂Cr₂O₇ and H₂SO₄ ) clearly to secure the reagent mark. Using the simplified symbol [O] is acceptable in equations, but name or give formulas for reagents.

❌ Common Errors

Forgetting to mention that the potassium dichromate must be acidified. Dichromate alone without acid will not bring about the oxidation.

Allocated marks: 2 marks (1 for reagent/catalyst, 1 for organic product).

Part (c): Substitution Reaction of 2-methylpropan-1-ol

(CH₃)₂CHCH₂OH

✅ Correct Answer

  • Organic Product: (CH₃)₂CHCH₂X (where X = Cl, Br, or I).
  • Reagent(s)/Catalyst: A halo-source matching your product, e.g., NaX AND H₂SO₄ / H⁺ (where X = Cl, Br, I), or HX .

💡 Key Knowledge

Substitution reactions of alcohols involve replacing the -OH group with a halogen atom to form a haloalkane using a halide salt in the presence of a strong acid.

🧠 Exam Technique

Consistency is vital! If you choose bromine as your halogen in the product ( (CH₃)₂CHCH₂Br ), your reagent must match ( NaBr and H₂SO₄ ). Mismatched pairs lose the reagent mark.

❌ Common Errors

Listing aluminium chloride ( AlCl₃ ) as a catalyst. AlCl₃ is used in Friedel-Crafts acylations/alkylations, not for converting alcohols into haloalkanes.

Allocated marks: 2 marks (1 for organic product, 1 for consistent reagents).

Part (d): Esterification Reaction of 2-methylpropan-2-ol

(CH₃)₃COH

✅ Correct Answer

  • Organic Product: A correct ester of (CH₃)₃COH , e.g., (CH₃)₃COOCCH₃ (t-butyl ethanoate).
  • Reagent(s)/Catalyst: A suitable carboxylic acid AND acid catalyst (e.g., CH₃COOH / H₂SO₄ ), OR an acyl chloride, OR an acid anhydride.

💡 Key Knowledge

Tertiary alcohols react with carboxylic acids in the presence of an acid catalyst (like concentrated sulfuric acid), or more reactive acyl derivatives, to form esters and water (or alternative byproducts).

🧠 Exam Technique

Draw the ester structure clearly showing the -COO- linkage connected correctly to the tertiary carbon skeleton derived from (CH₃)₃COH .

❌ Common Errors

Trying to use potassium dichromate ( Cr₂O₇²⁻ ) here. Tertiary alcohols are resistant to oxidation, so oxidizing agents are completely incorrect for esterification.

Allocated marks: 2 marks (1 for ester product, 1 for consistent reagents/catalyst).

Topics

Module 4: Core organic chemistry · Module 6: Organic chemistry and analysis · 4.2 Alcohols, haloalkanes and analysis · 6.1 Aromatic compounds, carbonyls and acids · 6.2 Nitrogen compounds, polymers and synthesis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.