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Organic chemistry
Alkenes
Electrophilic addition
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Cards (65)
What are electrophiles?
Electron pair acceptors attracted to
electron
density
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Why are alkenes susceptible to electrophilic attack?
High
electron density
in
carbon-carbon double bond
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What do curly arrows represent in reaction mechanisms?
Movement of
electron pairs
to break/form bonds
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What happens to the bromine molecule as it approaches the alkene?
Electrons
are repelled, creating partial charges
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What does the negatively charged bromide ion do after formation?
It forms a new bond with the
carbocation
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Why does bromine water turn colorless during the reaction?
Bromine atoms bond to
carbon
, losing color
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What are the characteristics of electrophiles and nucleophiles in the context of alkenes?
Electrophiles:
Electron pair acceptors
Attracted to high electron density
Often have a positive charge
Nucleophiles:
Electron pair donors
Repelled by high electron density
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What is the significance of the bromine water test in organic chemistry?
Confirms presence of
carbon-carbon double bonds
Color change from orange to colorless indicates reaction
Useful for identifying
unsaturated hydrocarbons
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What is the term for the breaking of a covalent bond where both electrons go to one atom?
Heterolytic fission
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How do halogen molecules differ from hydrogen halides in terms of dipoles?
Halogen molecules have an
induced dipole
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What are the key stages in the electrophilic addition of a halogen molecule to an alkene?
Bromine approaches alkene, inducing a dipole.
Alkene's
pi bond
attracts positive bromine, forming a bond.
Bromine bond breaks (heterolytic fission), creating a
carbocation
and bromide ion.
Bromide ion bonds with carbocation, forming the product.
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What are the differences between adding a halogen and a hydrogen halide to an alkene?
Halogen molecules have an
induced dipole
; hydrogen halides have a
permanent dipole
.
Adding hydrogen halides to
asymmetric
alkenes produces major and minor products; halogens produce one product.
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What is an alkene?
Unsaturated
hydrocarbons with a
double bond
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What is a polar bond or molecule?
Electrons
are unevenly distributed between
atoms
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What are electrophiles?
Electron pair acceptors
attracted to
electron density
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Why are alkenes susceptible to electrophilic attack?
They have a region of high
electron density
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What do curly arrows represent in reaction mechanisms?
Movement of
electron pairs
in bond formation
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Why can bromine react with an alkene despite being non-polar?
It gets polarized by the alkene's
double bond
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What happens to the bromine molecule as it approaches the double bond?
Electrons
are repelled, creating partial charges
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What does the partial positive charge on bromine indicate?
It is
electron deficient
and can accept electrons
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What is formed when the double bond breaks during the reaction?
A
carbocation
intermediate is formed
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What is a carbocation?
An ion with a
carbon atom
and
positive charge
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What happens to the bromide ion during the reaction?
It forms a new bond with the
carbocation
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What does bromine water test for?
Presence of
carbon-carbon double bonds
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What happens to the color of bromine water when it reacts with an alkene?
It turns from orange to colorless
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What are the key steps in the electrophilic addition mechanism of alkenes with bromine?
Bromine approaches the alkene double bond.
Electrons in bromine are repelled, creating partial charges.
The partially positive bromine acts as an electrophile.
A bond forms between bromine and one carbon atom.
The double bond breaks, forming a
carbocation
.
The bromide ion bonds with the carbocation.
A
di bromo
alkane is formed.
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What are the characteristics of electrophilic addition reactions?
Electrophiles are electron pair acceptors.
High electron density in double bonds attracts electrophiles.
Only one product is formed.
Both atoms from the electrophile are added to the alkene.
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What is the significance of the bromine water test in organic chemistry?
Tests for
unsaturation
in molecules.
Color change indicates presence of
double bonds
.
Useful for confirming
alkene
presence.
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How is a nucleophile defined?
As an
electron
pair donor
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What are the three electrophiles mentioned in the video?
Bromine
,
hydrogen bromide
,
sulfuric acid
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How does the mechanism of electrophilic addition start with bromine?
Through
induced dipole
formation
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What happens to the electrons in the bromine molecule during the reaction?
They cause
repulsion
and create an
induced dipole
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What is formed after the first step of the electrophilic addition mechanism?
An intermediate with a
positive carbon
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What is a carbocation?
A
positively charged
carbon atom
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What is the role of curly arrows in the mechanism?
They show the movement of
electrons
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What is the first step in the electrophilic addition mechanism with bromine?
Curly arrow from double bond to
bromine
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What is the significance of the positive charge on the carbocation?
It indicates
electron deficiency
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What is the role of the lone pair on the bromine ion in the final step?
It forms a bond with the
carbocation
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How does the addition of hydrogen bromide to ethane differ from bromine addition?
Hydrogen bromide
creates a
permanent dipole.
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What is positional isomerism in the context of propane and hydrogen bromide reaction?
Two different
carbocations
can form.
Leads to different products: 1-bromopropane and
2-bromopropane
.
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