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Give the products with their stereoisomers, if any. a. b. cis -2,- Dibromobut-2-ene c. trans-2,3- Dibromobut-2-ene d. e. underset("pent-2-ene")((H)"trans-2,3-Dibromo-")overset(H_(2)+PtO_(2))rarr(I) f.underset("pent-2-ene")((J)"cis-2,3-Dibromo-")overset(H_(2)+Pt+C)rarr(K) g. cis - But -2-eneoverset(D_(2)+Pt)rarr h. trans- But -2- eneoverset(D_(2)+Pd)rarr i. Why is the stereochemical product same when cis - or tans - pent -2- ene is hydrogenated with D_(2), in the presence of platinum ? j. Classify the two reactions :(i)hydrogenenation of alkene with transition metala (Pt or Pd or Ni) and (ii) hydrogenation with Wilkinson's catalyst in terms of catalyst used and their mechanism of hydrogenation with Wilkinson's catalyst. |
Answer» Solution : `a.` `b.` Note: Metal `+H_(2)` does not reduce `(R-X)` to `(R-H)` but reduces `(Ar-X)` to `(Ar-H)`. Reactant is cis `+` mechanism of addition is syn `rarr` product is meso.  `c.` Reactant is trans `+` mechanism of addition is syn `rarr` product is `dl` or `(+-)` racemic.  `d.` Reactant is cis `+` mechanism of addition is syn `rarr` product is meso.  Meso`-1,2-`dymethyl cyclohexane `(O.I.A.)` `e.` Reactant with two different GROUPS `+` mechanism of addition is syn `rarr` product is `dl` or `(+-)` or racemic.  `dl-2,3-` Dibromopentane `F.` Reactant is cis with two different groups `+` mechanism of addiciton is syn `rarr` product id `dl` or `(+-)` or racemic.  dl`-2,3-`Dibromopentane `g.` Reactant is cis `+` meachanism of addition is syn `rarr` product is meso.  `h.` Reactant is trans `+` mechanism of addition is syn `rarr` product is `(+-)`or `dl` or racemic.  `dl-2,3-`Dideutereo`-` butane `i.` Reactant cis or trans `(` with different groups `)+` mechanism of addiction is syn `rarr` Product is always `(+-)` or `dl` or racemic.  As there are two different groups in the alkene, the plane of symmetry is not attained. So the product is never obtained in meso from but optical isomers `d` and `l` are obtained from cis `-` or trans `-` alkene. `j.`  Both REACTIONS are catalytic hydrogenation. Reation `(1)` is HETEROGENOUS catalytic hydrogenation in which the solid catalyst is in a different phase from the reactant `(A)(` GAS phase `).` Reaction `(2)` is homogenous cataytic hydrogenation because the reactant and the catalyst are in the same gaseous phase. |
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