In order to distinguish between and which of the following reagents is useful?
1
Hinsberg test
2
-Naphthol
3
4
Official Solution
Correct Option: (2)
Step 1: Concept
To distinguish an aliphatic primary amine from an aromatic primary amine, the Azo-dye test is used. Step 2: Analysis
Aromatic amines like Aniline ( ) react with at to form stable diazonium salts, which then react with -naphthol to form a brightly colored dye. Step 3: Comparison
Aliphatic amines ( ) form unstable diazonium salts that decompose immediately, releasing Nitrogen gas and failing to form a dye. Step 4: Conclusion
Hence, -naphthol is the correct reagent for the Azo-dye test. Final Answer:(B)
02
PYQ 2022
medium
chemistryID: cuet-ug-
Which simple chemical test is used to distinguish between ethanal & propanal?
1
Iodoform test
2
Tollen's test
3
Fehling's test
4
Lucas test
Official Solution
Correct Option: (2)
The simple chemical test used to distinguish between ethanal (acetaldehyde) and propanal (propionaldehyde) is the Tollen's test.
Tollen's test is based on the oxidation of an aldehyde to a carboxylic acid in the presence of Tollens' reagent, which is an alkaline solution of silver nitrate Ethanal, being a primary aldehyde, readily undergoes oxidation in the Tollen's test and produces a silver mirror on the inner surface of the reaction vessel. Propanal, being a secondary aldehyde, does not react with Tollens' reagent and does not produce a silver mirror.
Therefore, the correct option is (B): the Tollen's test is used to distinguish between ethanal and propanal.
03
PYQ 2023
hard
chemistryID: cuet-ug-
Match List I with List II
List I
List II
A.
CH3CH2NH2
I.
N,N-Dimethylamiline
B.
II.
Ethylamine
C.
C6H5NH2
III.
Aniline
D.
C6H5N(CH3)2
IV.
Trimethylamine
Choose the correct answer from the options given below :
1
A-I, B-II, C-III, D-IV
2
A-II, B-I, C-III, D-IV
3
A-II, B-IV, C-III, D-I
4
A-III, B-II, C-I, D-IV
Official Solution
Correct Option: (1)
The correct option is (A) :A-I, B-II, C-III, D-IV.
04
PYQ 2023
hard
chemistryID: cuet-ug-
The correct increasing order of basic strength of amine is: (A) (B) (C) (D) Choose the correct answer from the options given below:
1
(A) only
2
(A) and (C) only
3
(A) and (B) only
4
(D) only
Official Solution
Correct Option: (1)
The correct option is (A) : (A) only
05
PYQ 2023
hard
chemistryID: cuet-ug-
Pick the incorrect statement about aniline.
1
Forms Zwitter ion when heated with Conc. H2SO4
2
Does undergo alkylation or acylation.
3
Undergoes diazotisation.
4
Produces foul smell when hested with chloroform and ethanolie KOH.
Official Solution
Correct Option: (2)
The correct option is (B) : Does undergo alkylation or acylation.
06
PYQ 2023
medium
chemistryID: cuet-ug-
In order to differentiate between N-methylmethanamine and N,N-Dimethylmethanamine, the reaction to be used is :
1
Carblyamine reaction
2
Gabriel Phthalimide reaction
3
Hoffmaun Bromanide reaction
4
Hinsberg's test
Official Solution
Correct Option: (4)
The correct option is (D) :Hinsberg's test.
07
PYQ 2023
medium
chemistryID: cuet-ug-
Aniline upon heating with conc. HNO3 and concentrated H2SO4 mixture gives.
1
o- and p-nitroaniline
2
o-Nitroaniline
3
Black terry mass
4
2,4,6-trinitroaniline
Official Solution
Correct Option: (3)
The correct option is(C):Black terry mass
08
PYQ 2023
medium
chemistryID: cuet-ug-
Aniline forms meta nitro derivative in strongly acidic medium. The reason is-
1
-NH2 group is meta directing
2
-NH2 group is o-p directing
3
Anilinium ion is meta directing
4
-NH2 group is highly reactive
Official Solution
Correct Option: (3)
The correct option is (C) :Anilinium ion is meta directing.
09
PYQ 2023
medium
chemistryID: cuet-ug-
Reaction of nitrous acid with aliphatic primary amine in cold gives.
1
A diazonium salt
2
An alcohol
3
A nitrite
4
A dye
Official Solution
Correct Option: (2)
The correct option is(B):An alcohol
10
PYQ 2024
medium
chemistryID: cuet-ug-
What is the major product of Carbylamine reaction?
1
Cyanide
2
Isocyanide
3
Nitrite
4
Alkane
Official Solution
Correct Option: (2)
The Carbylamine reaction, also known as the isocyanide test or Hofmann isocyanide synthesis, is an important reaction in organic chemistry used to synthesize isocyanides. In this reaction, a primary amine reacts with chloroform in the presence of a strong base like potassium hydroxide (KOH), leading to the formation of an isocyanide (RNC) as the major product. The reaction can be summarized as follows:
The products are isocyanide (RNC), potassium chloride (KCl), and water (H2O). The unique and characteristic foul smell of isocyanides makes this reaction a useful qualitative test for primary amines; however, it only works with aliphatic primary amines, not aromatic amines or secondary/tertiary amines.
In conclusion, among the given options, the major product of the Carbylamine reaction is isocyanide.
11
PYQ 2024
medium
chemistryID: cuet-ug-
Match List-I with List-II: Choose the correct answer from the options given below:
1
(A)- (II), (B)- (I), (C)- (IV), (D)- (III)
2
(A)- (II), (B)- (I), (C)- (III), (D)- (IV)
3
(A)- (I), (B)- (II), (C)- (IV), (D)- (III)
4
(A)- (I), (B)- (II), (C)- (III), (D)- (IV)
Official Solution
Correct Option: (2)
To solve the matching problem in Chemistry, we need to correctly link items from List-I with List-II. The provided correct answer is: (A)- (II), (B)- (I), (C)- (III), (D)- (IV).
12
PYQ 2024
hard
chemistryID: cuet-ug-
What will be the increasing order of basic strength of the following compounds:
1
2
3
4
Official Solution
Correct Option: (2)
To determine the increasing order of basic strength, we need to consider the factors that affect the basicity of amines:
Aliphatic vs. Aromatic Amines: Aliphatic amines (like C2H5NH2, (C2H5)2NH, (C2H5)3N) are generally more basic than aromatic amines (like C6H5NH2). This is because in aromatic amines, the lone pair of electrons on the nitrogen is delocalized into the benzene ring, making it less available for protonation.
Alkyl Groups: Alkyl groups are electron-donating, which increases the electron density on the nitrogen atom, making it more basic.
Steric Hindrance: In tertiary amines, the bulky alkyl groups can hinder the approach of a proton, reducing basicity.
Solvation Effects: In aqueous solutions, solvation of the protonated amine plays a significant role. Secondary amines are generally more solvated than tertiary amines.
Let's analyze the given compounds:
C2H5NH2 (Ethylamine): A primary aliphatic amine.
(C2H5)2NH (Diethylamine): A secondary aliphatic amine.
(C2H5)3N (Triethylamine): A tertiary aliphatic amine.
C6H5NH2 (Aniline): An aromatic amine.
Based on these factors:
Aniline (C6H5NH2) is the least basic due to resonance delocalization.
Among the aliphatic amines, secondary amines are generally the most basic due to a combination of inductive and solvation effects.
Primary amines are less basic than secondary amines but more basic than tertiary amines due to steric hindrance in tertiary amines.
Therefore, the increasing order of basic strength is:
Greater is the stability of the substituted ammonium cation, stronger should be the corre sponding amine as a base. Thus, the order of basicity of aliphatic amines should be: primary ¿ secondary ¿ tertiary, which is opposite to the inductive effect-based order. Secondly, when the alkyl group is small, like the-CH3 group, there is no steric hindrance to H-bonding. In case the alkyl group is bigger than the-CH3 group, there will be steric hindrance to H-bonding. Therefore, the change of nature of the alkyl group, e.g., from-CH3 to-C2H5 results in a change of the order of basic strength. Thus, there is a subtle interplay of the inductive effect, solvation effect, and steric hindrance of the alkyl group which decides the basic strength of alkyl amines in the aqueous medium.
