IB Chemistry Help Please.

Which reaction(s) involve(s) the formation of a positive ion?
I. CH3CH2CH2Br +OH−
II. (CH3)3CBr +OH−

A. I only
B. II only
C. Both I and II
D. Neither I nor II

The answer's B, but I don't get why.

Reply 1

charco

Study Forum Helper

the answer's B because its a tertiary halogenoalkane. These undergo nucloephilic substitution via an sN1 mechanism

(CH3)3C-Br <==> (CH3)3C+ + Br-
(CH3)3C+ + OH- --> (CH3)3C-OH

primary halogenoalkanes undergo via an sN2 reaction mechanism.

Reply 2

8937578

Hi guys

When you reflux a bromine halogenoalkane in an aqueous environment with Sodium or Potassium Hydroxide you get an alcohol and, I think, a Br+ ion.

That Br+ ion, does it just hang around or will it somwhow bond with others
forming Br2? What happens?

If it just does hang around, can you get it to come out of solution as Br2 if you electrolyse it?

Thanks

Reply 3

charco

Study Forum Helper

no you get a Br- ion... and yes, it just hangs around in aqueous solution.

If you were to electrolyse the solution maybe some bromine could be formed provided:
1. you keep the temperature high enough (bromine is a liquid at RT and it will redissolve in the water making bromine solution)
2. The solution of bromide ions is sufficiently strong otherwise all you will get at the anode is hydrogen.