[eureka123]

i am getting reverse order

[Schrödinger]

I am not sure, but i think the answer is IV>III>II>I

[eureka123]

its rite 

can u explain plzz

[macman104]

What happens when you mix an acid with HCl?  What is charged intermediate is being formed?

[Schrödinger]

Always, try to propose the mechanism first. It really helps.

Now, since the given compounds are in acidic medium, obviously, they have to be protonated first, and the only site available is the -OH group.

Once you protonate the -OH , you get a -OH₂⁺. Since water is a good leaving group, the intermediate you obtain is a carbocation.

The stability of the carbocation determines the rate, yield, reactivity, etc.
More stable is the intermediate, greater is the reactivity of the initial compound.

Now, in compound IV, the carbocation you get is a benzylic one, which is superbly stabilized by resonance.

In III, the intermediate is a secondary carbocation....hyperconjugation

In II and I, the inductive effect (-I effect) of fluorine will play a major role. If the positive charge is under the influence of a -I group, then its stability is lost. And, greater the proximity of the -I group, more is the damage done. So, II>I

[Schrödinger]

@ macman104 : Can you please explain your question, i couldn't understand it... like, what do you mean add another acid to HCl? Isn't HCl already an acid?

[macman104]

I'm sorry, I meant say an alcohol and HCl.  I was trying to get you to arrive at the formation of a carbocation on your own.  You then need to analyze each carbocation for stability.

[Arctic-Nation]

I might be going off on a tangent here, but is there a possibility of anchimeric assistance in I? Could a cyclic fluoronium ion be formed?

Or should this be kept simple?

[Schrödinger]

I think you are neglecting F's size and electronegativity ... so having a positive charge on F sounds a bit jarring.... so i think we should keep it simple

Please correct me if i am wrong

[eureka123]

thanx Schrödinger