Alkenes | OCR A-Level Chemistry A (H432)
Alkenes
- 86 questions
- 6 subtopics
- Module 4: Core organic chemistry
- Component 02 and Component 03
The double bond and what it does: sigma and pi bonding, E/Z isomerism, the addition reactions and their electrophilic mechanism with Markownikoff's rule, and addition polymers and their disposal..
It covers alkenes: the double bond, sigma and pi bonding, and shape, e/Z and cis-trans isomerism in alkenes, hydrogenation, halogenation and hydration of alkenes, electrophilic addition, carbocation stability and Markownikoff's rule, addition polymerisation and repeat units and waste polymers, and biodegradable and photodegradable alternatives.
Sample questions from Alkenes
Answer each one closed book first, then open the answer.
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Alkenes: the double bond, sigma and pi bonding, and shape
Why is there no free rotation about the carbon-carbon double bond in alkenes?
Show the answer
Rotation would break the sideways overlap of the p-orbitals that form the pi bond. -
Alkenes: the double bond, sigma and pi bonding, and shape
Why are alkenes much more reactive than alkanes?
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The π-bond in the C=C bond has a relatively low bond enthalpy, so it breaks easily, whereas alkanes contain only strong σ-bonds. -
E/Z and cis-trans isomerism in alkenes
What system of rules is used to assign E and Z labels to stereoisomers?
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The Cahn-Ingold-Prelog (CIP) priority rules. -
E/Z and cis-trans isomerism in alkenes
In cis-trans nomenclature, what does 'cis' indicate?
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Identical groups are on the same side of the double bond. -
Hydrogenation, halogenation and hydration of alkenes
What type of compound is formed when a halogen adds to an alkene?
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A dihaloalkane (a compound containing two halogen atoms) -
Hydrogenation, halogenation and hydration of alkenes
When HBr adds to an alkene, which atom attaches to one carbon of the former double bond?
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The hydrogen atom attaches to one carbon -
Electrophilic addition, carbocation stability and Markownikoff's rule
When representing the mechanism of halogen addition to an alkene, what two types of intermediate are both acceptable?
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A carbocation intermediate or a halonium ion intermediate -
Electrophilic addition, carbocation stability and Markownikoff's rule
How does the stability of a secondary carbocation compare to primary and tertiary carbocations?
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A secondary carbocation has intermediate stability (more stable than primary, less stable than tertiary)
The 6 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Alkenes: the double bond, sigma and pi bonding, and shape | Recall questions on unsaturation, how the sigma and pi bonds form, why there is no free rotation, and the trigonal planar shape and its angle. | 12 |
| E/Z and cis-trans isomerism in alkenes | Recall questions on what causes E/Z isomerism, the structural requirement at each carbon, the Cahn-Ingold-Prelog priority rules, and when cis and trans may be used instead. | 14 |
| Hydrogenation, halogenation and hydration of alkenes | Recall questions on the reagents and catalysts for each addition, the bromine water test and what a positive result shows, and the products formed. | 15 |
| Electrophilic addition, carbocation stability and Markownikoff's rule | Recall questions on why an electrophile is attracted to the double bond, the intermediate formed, the order of carbocation stability, and predicting the major product. | 17 |
| Addition polymerisation and repeat units | Recall questions on what happens to the double bond, deducing a repeat unit from a monomer and a monomer from a polymer, and naming the common addition polymers. | 16 |
| Waste polymers, and biodegradable and photodegradable alternatives | Recall questions on combustion and feedstock recycling, why burning PVC gives hydrogen chloride, and what biodegradable and photodegradable polymers achieve. | 12 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby sections
OCR A-Level Chemistry A Active Recall Guide
Every section, not just this one. 1,913 questions with their answers.