Question

Which of the following orders regarding the base strength of a leaving group in a reaction of an acid derivative with a nucleophile is correct?

• A. ${Cl}^{\ominus }>RCO{O}^{\ominus }>R{O}^{\ominus }$
• B. ${Cl}^{\ominus }>R{O}^{\ominus }>RCO{O}^{\ominus }$
• C. $R{O}^{\ominus }>RCO{O}^{\ominus }>{Cl}^{\ominus }$
• D. $R{O}^{\ominus }>{Cl}^{\ominus }>RCO{O}^{\ominus }$

Answer 1

Answer: (C)

$R{O}^{\ominus }>RCO{O}^{\ominus }>{Cl}^{\ominus }$

With an increase in electronegativity, basicity decreases, and the ability of the leaving group to leave increases. This is because an increase in electronegativity results in a species that wants to hold onto its electrons rather than donate them. The stronger the acid, the weaker the conjugate base.

Therefore the order of basicity is $R{O}^{-}>RCO{O}^{-}>C{l}^{-}$