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Electrophilic Addition

Posted: Thu Mar 16, 2017 8:36 pm
by Niveda_Tennety_1H
For an electrophilic addition reaction mechanism of a compound with a double bond and HBr, does the carbon to which the H is added matter?

Re: Electrophilic Addition

Posted: Fri Mar 17, 2017 9:42 am
by ssoroush 2B
No it doesn't. As long as the hydrogen bonds to a carbon before the bromine atom.

Re: Electrophilic Addition

Posted: Fri Mar 17, 2017 9:47 am
by Pratyush Kandimalla 2O
Since this is not part of 14B syllabus, I doubt it would make a difference which Carbon you attach the Halide to.
The question usually specifies the product formed, so just follow that.

This is how it works -->

ASYMMETRIC ACROSS DOUBLE BOND - both carbons have different number of hydrogens attached to them.

Electrophilic addition of a halogen acid across an asymmetric double bond is described by
Markovnikov's rule.
The negative part of the addendum goes to the carbon which contains the least number of Hydrogens

Addendum - What you are adding. In this case halogen acid HX (HBr, HF etc)
This means that the halide (X-) attaches to the carbon with the least number of hydrogens.

In addition to this, there is an Anti Markovnikov's rule which states that -
In the presence of a catalyst such as benzoyl peroxide, the negative part of the addendum goes to the carbon which contains the most number of Hydrogens .
This means that the halide (X-) attaches to the carbon with the most number of hydrogens.

This is the general method of looking at an electrophilic addition across a double bond.

Note: both the products are formed (halide on one carbon and the other), the major product however is the one following Markovnikov's rule.


SYMMETRIC ALKENE - both carbons across double bond have same number of hydrogens

The negative part of the addendum goes to that carbon which forms a more stable carbocation.
Different groups have different effect on of stability of carbocation,
thereby affecting the product.