13.4 - Electrophilic Addition in Alkenes Flashcards Preview

OCR A Chemistry A Level - Chapter 13 > 13.4 - Electrophilic Addition in Alkenes > Flashcards

Flashcards in 13.4 - Electrophilic Addition in Alkenes Deck (7)
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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

If the addition is between an alkene and a halogen, how is the dipole produced?

It is induced by the electron rich density of the pi bond.