A) III > II > IV > I
B) II > III > I >IV
C) II > III > IV > I
D) III > IV > II > I
Correct Answer: A
Solution :
[a] Key Idea Higher the tendency to give a proton, higher is the acidic character, and tendency to lose a proton depends upon the stability of intermediate, ie, carbanion formed. |
2, 4, 6-trinitrophenol after the loss of a proton gives 2, 4, 6-trinitrophenoxide ion which is stabilized by resonance, -I effect and -M effect, thus is most acidic among the given compounds. |
Phenol after losing a proton form phenoxide ion which is also stabilised by resonance, - M and -1 effects but is less stabilised as compared to 2, 4, 6-trinitrophenoxide ions. Thus, it is less acidic as compared to 2, 4, 6-trinitrophenol. |
(CH3COOH) after losing a proton gives acetate |
Ion ion which is stabilised by only |
resonance. However, it is more resonance stabilised as compared to a phenoxide ion, thus more acidic as compared to phenol. |
2, 4, 6-trinitrophenol, however, is more acidic than acetic acid due to the presence of three electron withdrawing NO2 groups. |
Cyclohexanol gives an anion that is least stable among the given, thus, it is least acidic. |
Hence, the correct order of acidic strength is 2, 4, 6-trinitrophenol > acetic acid > phenol > cyclohexanol III > II > IV > I |
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