WHAT IS THE REACTIVITY ORDER OF FOLLOWING CARBENES?

:CH₂ , :CF₂ , :CCl₂ , :CBr₂  . explain with reason clearly.

:CCl2 > :CBr2 > :CH2 > :CF2

WHAT HAPPENS:

This order is so because, :CF2 is relatively very stable due to back bonding.

comparing the left 3 carbenes.

the extent of back bonding is very poor, due to high energy difference in orbitals of the overlapping orbitals (:CH2 doesn't do back bonding)

therefore we come to know that Cl and Br impart unstability to the molecule, whereas H doesn't do anything to the carbene

therefore :CH2 is more stable than :CCl2 and :CBr2

so now we consider Inductive effect, which is certainly more for Cl and therefore :CCl2 is less stable than :CBr2.

hence the final order is:

(reactivity)

:CCl2 > :CBr2 > :CH2 > :CF2