Saved Bookmarks
| 1. |
Explain why the following general reaction takes place readily in the presence of small amount of NaI. R-Cl+R'-I overset(Na) rarr ROR'+NaCl. |
|
Answer» Solution :Although `R'O^(-)` is a GOOD NUCLEOPHILE, the given `S_(N)2` reaction occurs at a slower rate as `Cl^(Theta)` is not a good leaving group. In presence of `I^(Theta)`, the reaction actually takes place in two steps: ` RCI+I^(color(red)Theta)underset(("fast"))OVERSET(S_N2)(rarr)RI+CLl^(color(red)Theta), RI+R'O^(color(red)Theta)underset(("fast"))overset(S_(N)2)(rarr)ROR'+I^(color(red)Theta)` `I^(color (red) Theta)` is a stronger nucleouphile (more polarisable) than `R'O^(Theta)`. It readily displaces `Cl^(Theta)` from RCl. `I^(Theta)` is ALSO a good leaving group (weaker base and weaker C-I bond). So, it is readily displaced by `RO^(Theta)` and once again reacts in the first step. Thus, in presence of `I^(Theta)` as a catalyst the overall reaction occurs readily (THis is an EXAMPLE of a nucleophillic catalysis). |
|