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What happens when #H-X# adds to the double bond of an alkene?

Answer 1

The end result will be that one of the two bonds opens up. #H# adds to one side, and #X# to the other. This is called mono-halogenation.

(#X# stands for #F#, #Cl#, #Br# or #I#)

This is an example of an addition reaction, because the whole #HX# molecule is added tot the alkene. There are no other reaction products.

The mechanism is as follows: #H-X# is always very polar, the #X#-side drawing the electrons more to its side of the molecule. The extra electron pair in the double bond matches up with the (positive) #H# and then the #X# has 'no other choice' but matching up with the other side of the now open bond.

For instance, ethylene and hydrogen bromide

#(H_2C=CH_2)+ (H-Br)->(H_3C-CH_2Br)#

Extra: This reaction happens in relatively normal conditions, in contrast to the mono-halogenation of alkAnes.

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Answer 2

Elias Aguila

Hydrohalogenation occurs, forming a halogenoalkane. The double bond breaks, and the halogen adds to one carbon, while the hydrogen adds to the other.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.