Mechanism of the Reaction Between Ethene and Bromine - Carbonium Ion Formation
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The Br+ species needs two electrons for a stable octet of electrons in its outer energy level, how does it get these?
It attacks the C2H4 molecule
Why does the Br+ species attack the C2H4 molecule?
To try and gain the two electrons it needs for a stable octet of electrons in its outer energy level
Which of the two bromine ions formed attacks the C2H4 molecule?
The Br+ species
Where does the C2H4 molecule have the two electrons the Br+ species requires?
It has it in its pi bond
How does the Br+ ion get the two electrons it needs?
It attacks the C2H4
What does the Br+ ion do once it has its two electrons?
It forms a covalent bond with one of the carbon atoms using these electrons, one of which belong to the other carbon
What happens to the carbon who didn’t form the covalent bond with bromine?
It gains a positive charge due to the lost electron
How many carbons does the bromine form a covalent bond with?
It forms a bond with one carbon atom but it gets the electrons from each carbon (one from each carbon)
What is the positively charged carbon atom called?
Carbonium ion
What is a carbonium ion?
A positively charged carbon atom
What is the carbonium ion often referred to as?
An intermediate
What does the carbonium ion intermediate form?
There is reason to suggest it takes on a cyclic structure called a cyclic bromonium ion
Why can it be suggested that the carbonium ion intermediate takes on a cyclic structure called a cyclic bromonium ion?
The relatively large size of the bromine atom allows the formation of a three membered ring structure
List the events that occur during the carbonium ion formation. (5)
Br+ species attacks ethene for electrons Br+ forms covalent bond with one carbon using an electron from both carbons One carbon is not positively charged (carbonium ion) Carbonium ion = intermediate Carbonium ion intermediate = cyclic bromonium ion