Chapter 2: Q 49P (page 140)
Question: Ethyllithium is often used as a base in organic reactions,
(a)Predict the products of the following acid-base reaction,
(b) What is the conjugate acid of
? Would you expect
to be a strong base or a weak base?
Short Answer
(a)
(b)
Step by step solution
Bronsted – Lowry concept of acid and base
According to Bronsted-Lowry, an acid can be defined as any substance (molecule or ion) that has the tendency to donate a proton(H+) to any substance whereas a base can be defined as any substance (molecule or ion) that has the tendency to accept a proton(H+) from any other substance.
Conjugate acid-base pair
The residual part of acid after losing a proton (H+) will have a tendency to accept a proton(H+) . Therefore, it will behave as a base. These pairs of substances which differ from one another by a proton (H+) are known as conjugate acid-base pairs. Consider a general example of an acid:
Prediction of the products and explanation
(a) Bronsted-Lowry acid is a proton (H+)donor while Bronsted-Lowry base is a proton (H+)acceptor.
(b) The conjugate acid of CH3CH2Li is CH3-CH3 (or C2H6). Ethane (C2H6 )is a very weak acid because its pKa is around 50. Since it is a very weak acid therefore its conjugate base is a very strong base. Hence, CH3CH2Li can be expected to be a strong base.
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