I am learning about oxymercuration-demercuration reactions with alkenes and I wanted to know why this reaction occur?

 

 

 

 

I mean why would oxymercuration-deoxymercuration occur compared to it not occurring? Same with hyrdroboration-oxidation.

 

 

 

I mean why doesn't direct hyrdration just occur

 

 

 

 

 

I am learning about oxymercuration-demercuration reactions with alkenes and I wanted to know why this reaction occur?

 

 

 

 

I mean why would oxymercuration-deoxymercuration occur compared to it not occurring? Same with hyrdroboration-oxidation.

 

 

 

I mean why doesn't direct hyrdration just occur

 

 

Hello,

 

The reason a reaction occurs or does not occur is based on it's chemical potential. That is to say that reactions occur when the substrates are reactive - i.e. capable of perturbing each other. A good way to look at this is to study frontier molecular orbital theory. Which will describe what is called the homo-lumo gap of a molecule.

 

"Fukui realized that a good approximation for reactivity could be found by looking at the frontier orbitals (HOMO/LUMO). This was based on three main observations of molecular orbital theory as two molecules interact:

The occupied orbitals of different molecules repel each other.

Positive charges of one molecule attract the negative charges of the other.

The occupied orbitals of one molecule and the unoccupied orbitals of the other (especially the HOMO and LUMO) interact with each other causing attraction.

From these observations, frontier molecular orbital (FMO) theory simplifies reactivity to interactions between the HOMO of one species and the LUMO of the other. This helps to explain the predictions of the Woodward–Hoffmann rules for thermal pericyclic reactions, which are summarized in the following statement:

"A ground-state pericyclic change is symmetry-allowed when the total number of (4q+2)s and (4r)a components is odd"

(4q+2)s refers to the number of aromatic, suprafacial electron systems; likewise, (4r)a refers to antiaromatic, antarafacial systems. It can be shown that if the total number of these systems is odd then the reaction is thermally allowed.[2]"- http://en.wikipedia.org/wiki/Frontier_molecular_orbital_theory

 

After you become comfortable with the information provide above I'd suggest that you look at the reaction mechanisms for both the hydroboration and the oxymercuration. One gives you the Markonikov alcohol (oxymercuration) and the other gives you the anit-Markonikov alcohol. This is an important difference in the regioselectivities of their mechanisms, which you will want to be very familar with.

 

If you have any additional questions, please do not hesitate to come back and ask.

Cheers