ABC26OR0031 · General Organic Chemistry
Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Acidity Basicity · Exam: CSIR-NET DEC 2014 · Marks: 2 · Difficulty: Hard
The increasing order of pKa values of the circled hydrogens in the following compounds is 
(I) (II) (III)
(I) (II) (III)(a)I $<$ II $<$ III
(b)I $<$ III $<$ II
(c)II $<$ I $<$ III
(d)II $<$ III $<$ I
Answer
Answer (as printed): C
Explanation
Acidity is inversely proportional to pKa i.e. higher the pKa value, lower the acidity of the compound. (III) will generate a very unstable vinyl anion on removal of hydrogen. Thus, it has the highest pKa value. Between (I) and (II) II is more stabilized than I thus increasing its acidity and lowering its pKa value.
Explanation as extracted from the printed page; notation may be imperfect.