Flashcards in 13.4 - Electrophilic Addition in Alkenes Deck (7)
Loading flashcards...
1
Define electrophile
Atom or group of atoms that is attracted to an electron-rich centre where it ACCEPTS a pair of electrons.
- Usually a +ve ion or has partially positive charge
2
Why does a C=C attract electrophiles?
High electron density (due to pi bond presence), attracts electrophiles to accept an electron pair.
3
Describe the first step in the mechanism for electrophilic addition.
In the case of butene + hydrogen bromide
- HBr is a dipole due to the difference in electronegativity between the H and Br
1. Electron pair in pi-bond attracted to partially positive H. This breaks the double bond
HBr breaks by heterolytic fission
And the H of the H-Br bonds to the butene chain. This forms a carbocation and a Br-.
4
Describe the second step in the mechanism for electrophilic addition.
Br- reacts with the carbocation forming a haloalkane.
5
How is carbocation stability defined?
Primary carbocation - least stable
Secondary
Tertiary carbocation - most stable
6
What does carbocation stability have to do with electrophilic addition of unsymmetrical alkenes?
- The more stable the carbocation the more likely it is to form.
Markownikoff's rule states: The hydrogen will atack the carbon atom with the most amount of hydrogens attached to it and the least amount of carbons.
7