1
MCQ (Single Correct Answer)

AIPMT 2008

The stability of carbanions in the following.

is in the order of
A
(iv) > (ii) > (iii) > (i)
B
(i) > (iii) > (ii) > (iv)
C
(i) > (ii) > (iii) > (iv)
D
(ii) > (iii) > (iv) > (i)

Explanation

The carbonion which have more s-character will be more stable. Thus, the order of stability is :

(i) > (ii) > (iii) > (iv)
2
MCQ (Single Correct Answer)

AIPMT 2008

Which one of the following is most reactive towards electrophilic attack?
A
B
C
D

Explanation

Groups like, –Cl and –NO2 shows –I effect. –I groups attached to the benzene ring decrease the electron density in the benzene ring and hence less reactive towards electrophilic attack.

On the other hand, –OH not only shows –I effect but also +M effect which predominates the –I character and electron density is increased in the benzene ring which facilitates electrophilic attack.
3
MCQ (Single Correct Answer)

AIPMT 2008

Base strength of

is in the order of
A
(i) > (iii) > (ii)
B
(i) > (ii) > (iii)
C
(ii) > (i) > (iii)
D
(iii) > (ii) > (i)

Explanation

Weaker the acid, strongest is its conjugate base. Among alkane, alkene and alkyne, alkyne are most acidic and alkanes are least acidic, so the order of base strength is :

(i) > (ii) > (iii)
4
MCQ (Single Correct Answer)

AIPMT 2007

The order of decreasing reactivity towards an electrophilic reagent, for the following would be
(i) benzene
(ii) toluene
(iii) chlorobenzene
(iv) phenol
A
(ii) > (iv) > (i) > (iii)
B
(iv) > (iii) > (ii) > (i)
C
(iv) > (ii) > (i) > (iii)
D
(i) > (ii) > (iii) > (iv)

Explanation

Benzene having any activating group, i.e., OH, R etc. undergoes electrophilic substitution very easily as compared to benzene itself. Thus, toluene (C6H5CH3) and phenol (C6H5OH) undergo electrophilic substitution very readily than benzene. Chlorine with +E and +M effect deactivates the ring due to strong –I effect. So, it is difficult to carry out the substitution in chlorobenzene than in benzene, so correct order is

(iv) > (ii) > (i) > (iii)

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