Electrophilic Addition

Are hydrogenation of Alkenes (to form alkanes) and hydration of alkenes (to form alcohols) electrophilic addition reactions.
I’ve seen different things about this online and the OCR spec groups all of the Alkenes reactions as ‘addition reactions’.

Reply 1

Wombatsalamander

11

Original post by epicnm

Are hydrogenation of Alkenes (to form alkanes) and hydration of alkenes (to form alcohols) electrophilic addition reactions.
I’ve seen different things about this online and the OCR spec groups all of the Alkenes reactions as ‘addition reactions’.

Yes these would be, it’s addition as you are only adding atoms to the alkene, not removing any to do this, and it’s electrophilic as they are electron pair acceptors.

Reply 2

Davies Chemistry

9

Any reaction that involves one thing reacting with an alkene breaking the double bond and forming one product is an addition reaction.

C2H4 + H2 --> C2H6 is definitely addition

C2H4 + H2O --> C2H5OH is addition

C2H4 + Br2 --> C2H4Br2 is addition

C2H4 + HBr --> C2H5Br is addition

Reply 3

epicnm

OP

17

Original post by Wombatsalamander

Yes these would be, it’s addition as you are only adding atoms to the alkene, not removing any to do this, and it’s electrophilic as they are electron pair acceptors.

Original post by Davies Chemistry

Any reaction that involves one thing reacting with an alkene breaking the double bond and forming one product is an addition reaction.

C2H4 + H2 --> C2H6 is definitely addition

C2H4 + H2O --> C2H5OH is addition

C2H4 + Br2 --> C2H4Br2 is addition

C2H4 + HBr --> C2H5Br is addition

Ahhh that makes a lot more sense! Thank you!

Reply 4

username5510846

11

The hydrogenation reaction of alkenes to alkanes is not electrophilic addition. In hydrogenation, a nickel catalyst and hydrogen gas is used (and no electrophile is involved), and there is a different mechanism taking place. This mechanism involves adsorption of the alkene to the surface of the nickel catalyst, so it weakly forms bonds with the nickel catalyst which allows hydrogen to be added to the molecule. It is still an addition reaction, but is not electrophilic addition.

In terms of hydration, there is electrophilic addition involved.

In step one, a proton from the phosphoric acid catalyst acts as the electrophile and accepts a lone pair from the C=C double bond, forming a carbocation intermediate.

This site has a great explanation of the full mechanism: https://www.chemguide.co.uk/physical/catalysis/hydrate.html

Hope this helps, and anyone please correct me if there are any mistakes :smile:

Electrophilic Addition

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