Q21
CH 3 CHO and C 6 H 5 CH 2 CHO can be distinguished chemically by
Correct Answer
Option B
Solution
CH 3 CHO gives Iodoform test but C 6 H 5 CH 2 CHO does not give Iodoform test due to absence of methyl group.
Aldehydes, Ketones and Carboxylic Acids
Q22
The correct order of decreasing acid strength of trichloroacetic acid (A), trifluoroacetic acid (B), acetic acid (C) and formic acid (D) is
Correct Answer
Option A
Solution
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
Q23
The order of reactivity of phenyl magnesium bromide (PhMgBr) with the following compounds:
Correct Answer
Option D
Solution
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
Q24
Among the given compounds, the most susceptible to nucleophilic attack at the carbonyl group is
Correct Answer
Option D
Solution
CH 3 COCl is most susceptible to nucleophilic attack.
The susceptibility of a substrate towards nucleophilic attack depends on how good a leaving group is attached to it.
Cl – is a weak base and therefore a good leaving group.
Q25
Which of the following reactions will not result in the formation of carbon-carbon bonds?
Correct Answer
Option B
Solution
Here you can see no new C–C bond is formed in Cannizzaro reaction.
Q26
Propionic acid with Br 2 /P yields a dibromo product. Its structure would be
Correct Answer
Option C
Solution
This is Hell–Volhard–Zelinsky reaction.
In this reaction, acids containing -H react with Br 2 /red P giving product in which the -hydrogens are substituted by Br.
Q27
The relative reactivities of acyl compounds towards nucleophilic substitution are in the order of
Correct Answer
Option C
Solution
The more the basic character of the leaving group, the lesser is the reactivity the basic character follows the order NH 2 – > OR – > RCOO – > Cl – Hence, the relative reactivities of acyl compounds towards nucleophilic substitution follow the order Acyl halides > Acid anhydride > Ester > Amide.
Q28
A strong base can abstract an -hydrogen from
Correct Answer
Option A
Solution
As the carbonyl carbon is electron deficient so most susceptible to attack by ncleophilic reagent or base.
Thus -hydrogen is the easily obstructed from ketones by a base.
Q29
Consider the following compounds The correct decreasing order of their reactivity towards hydrolysis is
Correct Answer
Option C
Solution
The ease of hydrolysis depends upon the magnitude of the +ve charge on the carbonyl group.
Electron-withdrawing groups increase the magnitude of positive charge and electron donating groups decrease the magnitude of positive charge.
Hence, the decreasing order of reactivity towards hydrolysis is (ii) > (iv) > (i) > (iii)
Q30
Reduction of aldehydes and ketones into hydrocarbons using zinc amalgam and conc. HCl is called
Correct Answer
Option D
Solution
Clemmensen reduction : Aldehydes and ketones are reduced to the corresponding alkanes by means of amalgamated Zinc and HCl.
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