Question

Which of the following compounds is the weakest Bronsted base?

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Comparing basic strength

A Bronsted-Lowry base is a proton (hydrogen ion) acceptor. In this theory, an acid is a substance that can release a proton and a base is a substance that can accept a proton.

A) B) C) D)
In option $\left(A\right)$ and $\left(C\right)$ lone pair of electrons are in conjugation with the benzene ring. So, it is less available for protonation while in $\left(B\right)$ and $\left(D\right)$ lone pair of electrons do not participate in conjugation. Thus, $\left(A\right)$ and $\left(C\right)$ will be less basic as compared to $\left(B\right)$ and $\left(D\right)$.

In option $\left(C\right)$ lone pair is present on more electronegative atom (oxygen) as compared to $\left(A\right)$. So, it will have less tendency to accept protons by giving its electron pair. Hence, compound $\left(C\right)$ will be least basic. Hence, the correct answer is option $\left(C\right)$.