Question

Are akyl halides(I, Br, Cl) better leaving groups than tosylate, mesylate, and triflate?

this khan academy table ranks them and it seems like HI is the best leaving group

my teacher says these sulfonate esters are "super leaving groups".

Why are they "super" if they aren't even close to HI if HI is the best leaving group?

acid -pka conjugate base most H-I: -11 stable H-Br: : Br: 0:0 -s-6-H -3 !! So you see these halide anions O=o=0 o=o=0 0 1.12/6:52 Sn1 and Sn2: leaving group About Transcript

if my observation is incorrect and they are better leaving groups than akyl halides, please explain how.

thanks

Answer 1

Good leaving groups are weaker bases. The weaker the base, the better is the leaving ability.

HI is a better leaving group because its conjugate form the iodide ion is a conjugate acid. It is an acid so it cannot donate electrons and stay. It will rather accept electrons from other species and leave.

As mentioned sulfonate esters are also good leaving groups because the sulfonate anions are stabilised by resonance and are weaker bases.