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rate of hydrolysis of halogenoalkanes

it is know that as the electronegativity of X (halogen atom) increases, reaction rate of reaction decreases.

Can someone please explain why this is so?

Reply 1

eznot

If X acts as a reducing agent then it must lose an electron therefore as electronegativity increases it is harder to lose an electron, making X a weaker reducing agent and decreasing the rate of reaction

On the other hand, reactivity increases with electronegativity, if X is acting as an oxidising agent because one electron needs to be gained and this easier for a more electronegative atom.

It depends on the situation!

(Original post by Henny987)

it is know that as the electronegativity of X (halogen atom) increases, reaction rate of reaction decreases.

Can someone please explain why this is so?

Reply 2

Pigster

On the face of it, a more electronegative halogen should make the C-X bond more polar, i.e. will have a more delta +ve C. This should attract the nucleophile more strongly and hence increase the rate...

The other effect of changing the halogen is on bond strength (bond enthalpy). The weaker the bond is, the easier it is for the leaving group to, well, leave. The more electronegative the halogen, the stronger the bond and hence slower the rate...

Now there are two competing things here. It turns out that bond strength is more important than bond polarity and hence more electronegative halogens have slower hydrolysis reactions.

Original post by Henny987

it is know that as the electronegativity of X (halogen atom) increases, reaction rate of reaction decreases.

Can someone please explain why this is so?