3.3.4.2 Addition reactions of alkenes Flashcards
How is bromine used to test for unsaturation?
Electrophilic addition reaction occurs if a double bond is present
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What are the products when you add a hydrogen halide to an unsymmetrical alkene?
Markovnikov’s rule:
99% of the time: the hydrogen becomes attached to the carbon with the most hydrogens already attached to it
This is because it produces a more stable cation
The alkyl groups donate electron density (inductive effect)
What is the process when you add a hydrogen halide to an unsymmetrical alkene?
X (halogen) is more electronegative than the hydrogen
Bonding pair of electrons is attracted to the X
Hydrogen becomes slightly positively charged
The slightly positive hydrogen is the electrophile, and is attracted to the pi bond
Pi bond breaks and the electron pair swings down to form a bond with the hydrogen atom
At the same time, the electrons in the H-X bond are repelled right down on to the X to give an X- ion
Electrons can swing left or right to produce two different products
More likely to swing right because it is a quicker process and more stable
How do you represent the inductive effect on the carbon cation during electrophilic addition?
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What is the reaction for alkenes plus concentrated sulfuric acid with mechanisms?
Electrophilic addition
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How do you draw an electrophilic addition reaction between an alkene and a hydrogen halide with mechanisms?
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Step 1:
Arrow 1 = from double carbon bond to hydrogen atom
Arrow 2 = from H - Halogen bond to halogen atom
Step 2:
Arrow = from bromide ion to positively charged carbon atom
Forms a halogenoalkane
What is an electrophile?
Electron deficient atom or ion
Attacks areas of high electron density
What type of reaction occurs between sulfuric acid and alkenes?
Electrophilic addition
What is the formula for sulfuric acid in electrophilic addition?
HOSO3H
Why does Markovnikov’s rule exist?
A more stable cation is produced due to the inductive effect
