Question

Which of the following reactions are both stereospecific and regioselective ?
A. cis-But-2-ene + `D_2 overset (Pt) rarr`
B. cis-But-2-ene + `OsO_4 + NaHSO_3 rarr`
C. cis-But-2-ene + `Br_2 rarr`
D. trans-But-2-ene + `PhCO_3 H//H_2O rarr`.

Answer 1

Correct Answer - A::B::C
cis-Compound + Syn-addition of `D_2 rarr`

(b) cis-Compound + Syn-hydroxylation `rarr`

Hence it is both stereospecfic and regioselective.
(c) cis-Compound + Anti-addition of `Br_2 rarr`

So the reaction is sterospecific (anti-addition) but non-regioselective since two compounds of `(oplus)` and `(Ө)` form are formed in equal amounts.
trans-Compounds + Anti-hydroxylation `rarr`

So it is both stereospecific and regioselective.