Question

In organic chem we did an experiment called the addition of bromine to an alkene. We added bromine to trans-stilbene to create stilbene dibromide. The source of bromine was from a rapid equilibrium between pyridium tribromide and pyridium hydrobromide and bromine. The non-polar molecule of bromine became polarized when it approached the pi bond of the alkene and then is transferred to the alkene to create a cyclic bromonium ion and a bromide anion. One of the bromide anions attacks one of the carbon atoms of the cyclic bromonium ion to yield vicinal dibromide.  The solvent that was used acetic acid. Could we have done this same chemistry with iodine? Chlorine gas? Fluorine gas?

Answer 1

We could have same chemistry with chlorine gas with suitable result. But this process is very slow in case of iodine and too fast and vigorous for fluorine gas.

The main reason behind is their size. In halogen family iodine is the largest member so polarization by pi bond is quite difficult and slow. As polarization is of a molecule depends on its volume.

Where as in case of fluorine gas we know that it is the smallest member in periodic table. So it will polarize very fast reaction will start with uncontrollable speed and we could have a explosion.

The size of chlorine and bromine is almost same so this chemistry is possible for chlorine.