What happens in this reaction and why? 3-methylbutane-1,3-diol + cro3 -->

Here we have to explain and get the product of the reaction between 3-methyl-1,3-diol and chromium-tri-oxide (CrO₃)

The reaction between 3-methyl-1,3-diol with chromium-tri-oxide (CrO₃) form 3-methyl-3-hydroxybutanal.

The CrO₃ is used as a mild oxidant to the alcohol. It only produces aldehyde or ketone depending upon the position of the -OH group in a secondary or primary alcohol.

Here we can see there are two hydroxy (-OH) group in the reactant. However one of the hydroxy is at terminal carbon atom, thus primary alcohol and other in between as tertiary alcohol.

As the reagent CrO₃ does not reacts on the tertiary -OH group thus the -OH group present at 3 position will not be oxidized. Thus only the terminal hydroxy group will oxidize to form the corresponding aldehyde.

Henceforth the final product of the reaction is 3-methyl-3-hydroxybutanal as shown in the figure.  

adding or remove a gaseous reactant or product changes the concentrations. if the concentration of reactant or product is increased, the system will shift away from the side in which concentration was increased (i.e. if the concentration of reactants is increased, the system will shift toward the products. if more products are added, the system will shift to form more reactants). conversely, if the concentration of reactant or product is decreased, the system will shift toward the side in which concentration was decreased (i.e. if reactants are removed, the system will shift to form more reactants. if the concentration of products is decreased, the equilibrium will shift toward the products).

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