Addition of bromine on propene in presence of Brine yields a mixture of
Addition of bromine on propene in presence of Brine yields a mixture of
Consider the following reaction
CH3−CH=CH2−→−−−−Br2/NaCl?
First of all, the ππ-electrons will attack an electrophile which in this case is a Br+BrX+ which is obtained form polarisation of the Br−Br and it is added to the less substituted carbon, which complies with Markovnikov's rule, forming the carbocation below:
CH3−CH+−CH2−Br
*The first step is Br−BrBr−Br approaching the pi-cloud, being polarized, loosing a Br−BrX−to form a 3-cyclic bromonium cation. Given solubility and reactively inert solvent, Br−BrX− (large poor nucleophile) competes with Cl−ClX− (smaller, better nucleophile) for ring-opening capture. Now factor in relative concentrations. Now factor in thermodynamics (reversibility, Cl−ClX− wins for the stronger C−ClC−Cl bond) versus kinetics (smaller Cl−ClX− vs. initial tight ion pair rapidly collapsing to product). Temperature probably makes a product ratio difference, too.
If your linear ion intermediate is controlling, the ClCl comes in at the 2-position by default. If my cyclic ion intermediate is controlling, the ClCl comes in at the 1-position by steric hindrance. And if you do it in water, you get halohydrin byproducts.
Keep the reaction way from light or you will get radical abstraction and allylic substitution.
CH3−CH=CH2−→−−−−Br2/NaCl?
First of all, the ππ-electrons will attack an electrophile which in this case is a Br+BrX+ which is obtained form polarisation of the Br−Br and it is added to the less substituted carbon, which complies with Markovnikov's rule, forming the carbocation below:
CH3−CH+−CH2−Br
*The first step is Br−BrBr−Br approaching the pi-cloud, being polarized, loosing a Br−BrX−to form a 3-cyclic bromonium cation. Given solubility and reactively inert solvent, Br−BrX− (large poor nucleophile) competes with Cl−ClX− (smaller, better nucleophile) for ring-opening capture. Now factor in relative concentrations. Now factor in thermodynamics (reversibility, Cl−ClX− wins for the stronger C−ClC−Cl bond) versus kinetics (smaller Cl−ClX− vs. initial tight ion pair rapidly collapsing to product). Temperature probably makes a product ratio difference, too.
If your linear ion intermediate is controlling, the ClCl comes in at the 2-position by default. If my cyclic ion intermediate is controlling, the ClCl comes in at the 1-position by steric hindrance. And if you do it in water, you get halohydrin byproducts.
Keep the reaction way from light or you will get radical abstraction and allylic substitution.
