JEE PYQ: General Organic Chemistry Question 16
Question 16 - 2020 (02 Sep Shift 2)
Arrange the following labelled hydrogens in decreasing order of acidity:
(i) $\text{H}$ on $\text{C} \equiv \text{C}-\text{H}$ adjacent to $\text{NO}_2$ (ii) $\text{H}$ on $\text{COO}-\text{H}$ (iii) $\text{H}$ on $\text{O}-\text{H}$ (phenolic) (iv) $\text{H}$ on $\text{O}-\text{H}$ (alcoholic)
(1) (ii) > (i) > (iii) > (iv)
(2) (iii) > (ii) > (iv) > (i)
(3) (ii) > (iii) > (iv) > (i)
(4) (iii) > (ii) > (i) > (iv)
Show Answer
Answer: (3)
Solution
Acidic strength $\propto$ stability of conjugate base. General order of acidic strength is: R-COOH > Ph-OH > R-C$\equiv$CH. In between (iii) and (iv), (iii) is more acidic due to $-\text{M}$ effect of $-\text{NO}_2$. Thus, decreasing order of acidity is (ii) > (iii) > (iv) > (i).
BETA
