What type of hydrocarbons are alkenes classified as?
Unsaturated hydrocarbons
They contain at least one carbon–carbon double bond.
What type of bond is present between carbon atoms in alkenes?
Double covalent bond
The C=C bond consists of one σ bond and one π bond.
Fill in the blank:
The carbon–carbon double bond in alkenes is a region of high _______ density.
electron
This makes alkenes more reactive than alkanes.
True or False:
Alkenes are more reactive than alkanes due to the presence of a double bond.
True
The electron-rich double bond attracts electrophiles.
What are the two types of bonds present in a carbon–carbon double bond?
Sigma and pi
The σ bond forms by head-on overlap and the π bond by sideways overlap.
True or False:
The π bond in alkenes is stronger than the σ bond.
False
The π bond is weaker and more easily broken in reactions.
Fill in the blank:
The double bond in alkenes restricts _______ about the carbon–carbon bond.
rotation
This restriction leads to E–Z stereoisomerism.
Why do alkenes undergo many addition reactions?
High electron density
The π bond attracts electrophiles.
True or False:
The electron density in an alkene is concentrated above and below the plane of the molecule.
True
This is due to the π bond formed by sideways overlap of p orbitals.
Fill in the blank:
The π bond is formed by sideways overlap of _______ orbitals.
p
These orbitals form electron density above and below the bond axis.
What type of reactions are typical for alkenes due to their double bond?
Addition reactions
The π bond breaks allowing new atoms to add across the double bond.
Why is the double bond in alkenes considered a reactive site?
Electron-rich region
The high electron density attracts electron-deficient species.
What type of reaction commonly occurs when alkenes react with small molecules such as HBr or Br2?
Electrophilic addition
The π bond breaks and atoms add across the C=C bond.
What type of species attacks the electron-rich double bond in alkenes?
Electrophile
Electrophiles are electron-pair acceptors attracted to high electron density.
Fill in the blank:
In electrophilic addition, the alkene double bond acts as a source of _______.
electrons
The π bond donates electrons to the electrophile.
True or False:
Bromine water can be used to test for unsaturation in organic molecules.
True
Alkenes decolourise orange bromine water.
What observation indicates the presence of a carbon–carbon double bond when bromine water is added?
Decolourisation
The orange colour disappears as bromine reacts with the alkene.
True or False:
Electrophilic addition reactions proceed through a carbocation intermediate.
True
The intermediate forms after the electrophile attacks the double bond.
Fill in the blank:
The positively charged intermediate formed during electrophilic addition is called a _______.
carbocation
Its stability influences which product forms.
Which carbocation is most stable: primary, secondary, or tertiary?
Tertiary
Tertiary carbocations are stabilised by surrounding alkyl groups. This is because alkyl groups have a positive inductive effect.
True or False:
The most stable carbocation usually leads to the major product of the reaction.
True
Reaction pathways favour the most stable intermediate.
Fill in the blank:
When an unsymmetrical alkene reacts with HBr, the hydrogen attaches to the carbon with the _______ hydrogens.
most
This forms the more stable carbocation intermediate.
What term describes the main product formed in a reaction when multiple products are possible?
Major product
It forms through the most stable reaction pathway.
Why can minor products form during electrophilic addition reactions?
Alternative carbocation formation
Less stable intermediates can still form in smaller amounts.
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3.1.1 Atomic structure50
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3.1.2 Amount of substance47
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3.1.3 Bonding90
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3.1.4 Energetics62
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3.1.5 Kinetics55
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3.1.6 Equilibria & Kc24
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3.1.7 Redox equations17
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3.1.8 Thermodynamics27
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3.1.9 Rate equations24
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3.1.10 Kp12
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3.1.11 Electrode potentials46
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3.1.12 Acids and bases69
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3.2.1 Periodicity22
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3.2.2 Group 2 metals24
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3.2.3 Group 7 (halogens)31
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3.2.4 Period 3 oxides35
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3.2.5 Transition metals95
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3.2.6 Ions in aqueous solution39
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3.3.1 Intro to organic chemistry42
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3.3.2 Alkanes49
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3.3.3 Halogenoalkanes36
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3.3.4 Alkenes36
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3.3.5 Alcohols43
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3.3.6 Organic analysis36
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3.3.7 Optical isomerism12
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3.3.8 Aldehydes & ketones20
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3.3.9 Carboxylic acids & derivatives25
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3.3.10 Aromatic chemistry29
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3.3.11 Amines41
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3.3.12 Polymers24
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3.3.13 Amino acids, proteins, DNA61
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3.3.14 Organic synthesis12
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3.3.15 NMR spectroscopy14
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3.3.16 Chromatography12
