AQA A-Level Chemistry (3.3.4) – Alkenes.
Exam Questions And Correct Answers
Alkene definition - answerUnsaturated hydrocarbons.
General formula of alkenes - answerCnH2n
What is required somewhere in the structure of alkenes? - answerA carbon-carbon double
bond.
What is the arrangement of bo...
What is required somewhere in the structure of alkenes? - answer✔✔A carbon-carbon double
bond.
What is the arrangement of bonds around the C=C? (Shape and bond angle) - answer✔✔Planar,
120 degrees.
When do numbers needed to be added to the name? - answer✔✔When positional isomers can
occur.
What is stereoisomerism? - answer✔✔Stereoisomers have the same structural formulae but have
a different spatial arrangement of atoms.
What type of isomerism can alkenes exhibit? - answer✔✔E-Z stereoisomerism.
Why do E-Z isomers exist? - answer✔✔Due to restricted rotation about the C=C bond.
When do E/Z stereoisomers arise? - answer✔✔(a) There is restricted rotation around the C=C
double bond.
(b) There are two different groups/atoms attached both ends of the double bond.
What type of bonds easily rotate? - answer✔✔Single carbon-carbon covalent bonds.
Z-but-2-ene - answer✔✔
E-but-2-ene - answer✔✔
How do you name E-Z stereoisomers? - answer✔✔1) Determine the priority groups on both
sides of the double bond.
2) If the priority atom is on the same side of the double bond it is labelled Z from the german
zusammen (The Zame Zide!).
3) If the priority atom is on the opposite side of the double bond it is labelled E from the german
entgegen (The Epposite side!).
What is the priority group? - answer✔✔The atom with the bigger Atomic number is classed as
the priority atom.
Electrophile definition - answer✔✔An electron pair acceptor.
Addition reaction definition - answer✔✔A reaction where two molecules react together to
produce one.
What type of reaction do alkenes undergo? - answer✔✔Addition reactions.
Why do alkenes experience addition reactions? - answer✔✔The double bonds in alkenes are
areas with high electron density. This attracts electrophiles and the alkenes undergo addition
reactions.
Reaction of bromine with alkenes
What is the change in functional group? - answer✔✔Alkene → dihalogenoalkane
Reaction of bromine with alkenes
What is the reagent? - answer✔✔Bromine.
Reaction of bromine with alkenes
What is the conditions? - answer✔✔Room temperature (not in UV light).
Reaction of bromine with alkenes
What is the mechanism? - answer✔✔Electrophilic addition.
Reaction of bromine with alkenes
What is the type of reagent? - answer✔✔Electrophile Br+.
Reaction of bromine with alkenes
mechanism example with methene - answer✔✔
Reaction of bromine with alkenes
What happens to the alkene in terms of polarity when this reaction takes place? - answer✔✔As
the Br2 molecule approaches the alkene, the pi bond electrons repel the electron pair in the Br-Br
bond. This INDUCES a DIPOLE. Br2 becomes polar and ELECTROPHILIC (Brδ+ ).
Reaction of bromine with alkenes
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