1
MCQ (Single Correct Answer)

AIPMT 2012 Mains

Consider the reaction :
RCHO + NH2NH2 $$ \to $$ RCH $$=$$ N $$-$$ NH2

What sort of reaction is it?
A
Electrophilic addition-elimination reaction
B
Free radical addition-elimination reaction
C
Electrophilic substitution-elimination reaction
D
Nucleophilic addition-elimination reaction

Explanation

RCHO + NH2NH2 $$ \to $$ RCH $$=$$ N $$-$$ NH2

Such reactions take place in slightly acidic medium and involve nucleophilic addition of the ammonia derivative.
2
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

The correct order of decreasing acid strength of trichloroacetic acid (A), trifluoroacetic acid (B), acetic acid (C) and formic acid (D) is
A
B > A > D > C
B
B > D > C > A
C
A > B > C > D
D
A > C > B > D

Explanation

As –I effect increases, COOH group becomes more electron deficient and tendency to loose H+ ions increases i.e., acid strength increases. As +I effect increases, acid strength decreases. Thus, correct order of acid strength is
3
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

CH3CHO and C6H5CH2CHO can be distinguished chemically by
A
Benedict's test
B
Iodoform test
C
Tollen's reagent test
D
Fehling's solution test

Explanation

CH3CHO gives Iodoform test but C6H5CH2CHO does not give Iodoform test due to absence of methyl group.
4
MCQ (Single Correct Answer)

AIPMT 2011 Mains

The order of reactivity of phenyl magnesium bromide (PhMgBr) with the following compounds:
A
III > II > I
B
II > I > III
C
I > III > II
D
I > II > III

Explanation

The reactivity of the carbonyl group towards the nucleophilic addition reactions depend upon the magnitude of the positive charge on the carbonyl carbon atom (electronic factor) and also on the crowding around the carboxyl carbon atom in the transition state (steric factor). Both these factors predict the following order
I > II > III

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