Grade 12 Physical Sciences · Matter and Materials

Write elimination reactions and conditions

Write elimination reactions where a small molecule is removed to form a double bond, and give their conditions (ethanol → ethene + H₂O).

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Elimination reactions Organic Chemistry ReactionsMiss Martins Maths and Science

Reactions Organic Chemistry Grade 12 | Haloalkane to AlkeneKevinmathscience

6 Gr 12 Physical Science - Reactions in Organic Chemistry - Dehydration Elimination ReactionJuniorTukkie at the University of Pretoria

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Question 1.3 · November 2024 · Paper 2 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E.

1.3 Study the reactions below.

Reaction 1:

CH_{3} CH_{2} CHOHCH_{3} H_{2} SO_{4} conc.

Compound P (major product) +

H_{2} O

Reaction 2: Compound P

hydrogenation

Compound Q

Which ONE of the following combinations is the CORRECT IUPAC names of compounds P and Q?(2)

A P: But-1-ene; Q: Butane
B P: But-2-ene; Q: Butane
C P: But-1-ene; Q: Butan-2-ol
D P: But-2-ene; Q: Butan-2-ol

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: write elimination reactions and conditions

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3. Question 4.2.7 · November 2023 · Paper 2 · National (DBE) · 2 marks
4.2 Consider the equations for reactions I to III below.

A and B represent organic compounds that are POSITIONAL ISOMERS.
X is an inorganic product.

Write down the:
4.2.7 Write down TWO terms that describe this type of reaction.(2)
Show the memo (2 ticks)Memo
1. ✓
  First termElimination
  1 mark · Write elimination reactions and conditions
2. ✓
  Second termDehydrohalogenation / dehydrochlorination
  1 mark · Write elimination reactions and conditions
4. Question 4.6.2 · November 2024 · Paper 2 · National (DBE) · 3 marks
Study the flow diagram below.

Reaction I is a CRACKING REACTION forming two organic compounds, W and T, as the ONLY products.
4.6 Compounds R and T are positional isomers.

The inorganic reagents shown below are available for reactions IV and V.

$Br_{2}$ ; $H_{2} SO_{4}$ (conc.); NaOH(conc.); HBr; $H_{2}$

Write down:
4.6.2 The balanced equation for reaction V, using STRUCTURAL formulae and the correct reagent shown above(3)
Show the memo (3 ticks)Memo
1. ✓
  NaOH2-bromobutane + NaOH
  1 mark · Write elimination reactions and conditions
2. ✓
  Whole structural formula of alkene correct (functional group on second/first C atom)But-2-ene, $CH_{3} CH=CHCH_{3}$ , drawn with all bonds and H atoms (or but-1-ene from 1-bromobutane)
  1 mark · Draw structural formulae
3. ✓
  NaBr + H $_{2}$ O+ NaBr + $H_{2} O$
  1 mark · Write elimination reactions and conditions
5. Question 4.1.5 · November 2025 · Paper 2 · National (DBE) · 2 marks
4.1 Study the three organic reactions I, II and III below. Compounds T and W are organic compounds. R and S are inorganic substances. Consider only the major products.

Reaction I: $HBr(g) + T \to W$
Reaction II: $W + NaOH(aq) \to CH_{3} CH(OH)CH_{2} CH_{3} + R$
Reaction III: $CH_{3} CH(OH)CH_{2} CH_{3} S T + H_{2} O (ℓ)$

Write down the:
4.1.5 STRUCTURAL formula of compound T(2)
Show the memo (2 ticks)Memo
1. ✓
  (a) Correct functional groupThe C=C double bond between carbon 2 and carbon 3 (but-2-ene, the major product).
  1 mark · Write elimination reactions and conditions
2. ✓
  (b) Whole structure correct $CH_{3} -CH=CH-CH_{3}$ drawn with all bonds and all 8 H atoms.
  1 mark · Draw structural formulae
6. Question 4.2 · May/June 2025 · Paper 2 · National (DBE) · 2 marks
In the flow diagram below, a primary alcohol P is used as a starting reactant to form different organic compounds under different reaction conditions.
4.2 Write down the IUPAC name of compound P.(2)
Show the memo (2 ticks)Memo
1. ✓
  Correct chain length (But)Chain length: but- (4 C atoms)
  1 mark · Write elimination reactions and conditions
2. ✓
  Everything else correctButan-1-ol
  1 mark · Write IUPAC names

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