Arrange the following compounds in decreasing order of acidity for the indicated proton (H): (i) (ii) (iii)

Step-by-step solution

The acidity of a compound depends on the stability of its conjugate base. The removal of the indicated proton (H) from the C9 position of the fluorene ring generates a carbanion. In compound (ii), the conjugate base is an ylide where the negative charge on the carbon atom is stabilized by strong p -d back-bonding (resonance) into the vacant d-orbitals of the adjacent phosphorus atom, in addition to the -I effect of the - + P Me₃ group. In compound (i), the nitrogen atom in the - + N Me₃ group lacks vacant d-orbital