| Among the following four compounds [AIPMT (M) 2010] |
| A. Phenol |
| B. Methyl phenol |
| C. meta-nitrophenol |
| D. para nitrophenol the acidity order is |
A) \[D>C>A>B\]
B) \[C>D>A>B\]
C) \[A>D>C>B\]
D) \[B>A>C>D\]
Correct Answer: A
Solution :
| [a] An electron withdrawing group (1 showing group like \[-N{{O}_{2}},-CN)\] stabilises the phenoxide ion, thus when present, increases the acidity of phenol. On the other hand electron releasing groups (+I showing group like \[-C{{H}_{3}}-{{C}_{2}}{{H}_{5}}),\] when present, decrease the acidity of phenol by destabilizing peroxide ion. Hence, the correct order of acidity of given compounds is |
| \[\underset{\text{(D)}}{\mathop{\text{p-nitrophenol}}}\,>\underset{\text{(C)}}{\mathop{\text{m-nitrophenol}}}\,>\underset{\text{(B)}}{\mathop{\underset{\text{methyal}\,\text{phenol}}{\mathop{\underset{\text{(A)}}{\mathop{\text{phenol}}}\,}}\,}}\,\](due to intermolecular H bonding) |
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