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Basic strength of amines and heterocycles

55 questions on Basic strength of amines and heterocycles from the General Organic Chemistry II: Acids and Bases chapter: 11 NEET level, 22 JEE Main, 22 JEE Advanced. Each one opens with its answer and solution.

Practice this topic All General Organic Chemistry II: Acids and Bases topics

Which of the following is the strongest base in aqueous solution? NEET level
Aniline is a weaker base than cyclohexylamine mainly because NEET level
Which is the correct order of basic strength of methylamines in aqueous solution? NEET level
In pyridine the lone pair on nitrogen is available for protonation because it NEET level
Pyrrole is practically non-basic because NEET level
Which of the following is the strongest base? NEET level
Among the following carbanions or anions, the weakest base is (pKa of conjugate acids: ethane about 50, ethyne 25, ammonia 38, ethene about 44) NEET level
Which of the following is the weakest base? NEET level
Which of the following is the strongest base in aqueous solution? NEET level
Guanidine, HN=C(NH2)2, is a very strong organic base (pKaH of guanidinium = 13.6) because NEET level
Which of the following is the strongest base? NEET level
Which is the correct order of basic strength of ethylamines in aqueous solution? JEE Main level
Arrange in decreasing order of basic strength in the gas phase: CH3NH2, (CH3)2NH, (CH3)3N. JEE Main level
In aqueous solution (CH3)3N is a weaker base than (CH3)2NH because JEE Main level
Assertion (A): Pyrrole is a much weaker base than pyridine. Reason (R): The nitrogen lone pair in pyrrole is part of the aromatic pi sextet, whereas in pyridine... JEE Main level
In 1H-imidazole (the ring has N-1 bearing an H atom and N-3 without H), protonation by an acid occurs at JEE Main level
Arrange in decreasing order of basic strength in aqueous solution: aniline, 4-nitroaniline, 2,4-dinitroaniline. JEE Main level
Arrange in decreasing order of basic strength in aqueous solution (approximate pKaH: benzylamine 9.3, aniline 4.6, acetanilide about -1): benzylamine, aniline, ... JEE Main level
When acetamide, CH3CONH2, is protonated in strong acid, the proton adds mainly to JEE Main level
Arrange in decreasing order of basic strength in aqueous solution using pKaH values (guanidine 13.6, methylamine 10.6, pyridine 5.2, aniline 4.6): guanidine, me... JEE Main level
Arrange the conjugate bases in decreasing order of basic strength using pKa values of the conjugate acids (ethanol 15.9, phenol 10.0, acetic acid 4.76): CH3CH2O... JEE Main level
Arrange in decreasing order of basic strength (pKa of conjugate acids: methane about 48, ammonia 38, water 15.7, HF 3.2): CH3-, NH2-, OH-, F-. JEE Main level
Sodium hydride is added to dry ethanol. The main change is JEE Main level
Pyrimidine (pKaH = 1.3) is a much weaker base than pyridine (pKaH = 5.2) because JEE Main level
Arrange in decreasing order of basic strength in water: CH3CH2NH2, CH3CH=NH, CH3C#N (hint: consider the hybridisation of the nitrogen lone pair). JEE Main level
Aniline dissolves readily in dilute aqueous HCl but acetanilide does not, because JEE Main level
The conjugate acid of piperidine has pKa = 11.1 at 298 K. Using pK_a + pK_b = 14, find the pK_b of piperidine. Give the answer to one decimal place. JEE Main level
Select the correct statement(s). JEE Main level
Which of the following are stronger bases than aniline (pKaH 4.6) in aqueous solution? JEE Main level
Which of the following are stronger bases than hydroxide ion? (pKa of conjugate acids: H2 about 35, methane about 48, phenol 10.0, acetic acid 4.76, water 15.7) JEE Main level
In which of the following is the nitrogen lone pair a part of the aromatic pi sextet (so that it is not the site of protonation)? JEE Main level
Which of the following statements about guanidine, HN=C(NH2)2, are correct? JEE Main level
Which of the following pairs are correctly arranged with the stronger base first (in aqueous solution)? JEE Main level
Arrange in decreasing order of basic strength in aqueous solution using approximate pKaH values (methylamine 10.6, pyridine 5.2, aniline 4.6, acetamide -0.5): C... JEE Advanced level
Piperidine and aniline have conjugate acids with pKa 11.1 and 4.6 respectively. The ratio K_b(piperidine)/K_b(aniline) in water at 298 K is approximately JEE Advanced level
A buffer has pH 6.2. For imidazole (pKa of imidazolium = 7.0), the ratio [imidazolium]/[imidazole] in this buffer is closest to JEE Advanced level
4-Aminopyridine (pKaH 9.2) is a much stronger base than pyridine (5.2). In it, protonation occurs at the ring nitrogen because JEE Advanced level
4-Nitroaniline (pKaH 1.0) is a weaker base than 3-nitroaniline (pKaH 2.5) mainly because JEE Advanced level
Assertion (A): Acetanilide is a far weaker base than aniline. Reason (R): In acetanilide the nitrogen lone pair is delocalised towards the carbonyl oxygen in ad... JEE Advanced level
Acetylene (pKa 25) is to be converted completely into its sodium salt. Which reagent in an inert solvent is NOT suitable? (pKa of conjugate acids: NH3 38, H2 ab... JEE Advanced level
For CH3CH2O- + C6H5OH <=> CH3CH2OH + C6H5O- in water at 298 K (pKa: ethanol 15.9, phenol 10.0), the equilibrium constant is closest to JEE Advanced level
Arrange in decreasing order of basic strength using pKaH values (piperidine 11.1, pyridine 5.2, pyrimidine 1.3, pyrrole -3.8): piperidine, pyridine, pyrimidine,... JEE Advanced level
One equivalent of dilute HCl is added to an equimolar aqueous mixture of CH3NH2 (pKaH 10.6) and C6H5NH2 (pKaH 4.6), the amounts of HCl and of each amine being e... JEE Advanced level
Acetamidine, CH3C(=NH)NH2 (pKaH about 12.4), is a far stronger base than acetamide (pKaH about -0.5). The best explanation is that JEE Advanced level
Methylammonium ion has pKa = 10.6 at 298 K. Using the weak-base approximation [OH-]=sqrtK_b c, the pH of a 0.1 M aqueous solution of methylamine is closest to JEE Advanced level
Anilinium ion has pKa = 4.6 at 298 K. Using the weak-base approximation [OH-]=sqrtK_b c, the pH of a 0.1 M aqueous solution of aniline is closest to JEE Advanced level
Nicotine consists of an N-methylpyrrolidine ring attached through its C-2 to C-3 of a pyridine ring. With one equivalent of acid, the proton goes mainly to JEE Advanced level
On treatment with strong acid, pyrrole is protonated mainly at C-2 rather than at nitrogen because JEE Advanced level
Nitration of aniline with a mixture of conc. HNO3 and conc. H2SO4 gives a substantial proportion of the meta-nitro product. The reason is that JEE Advanced level
Imidazolium has pKa = 7.0 and pyridinium has pKa = 5.2 at 298 K. Using pK_a+pK_b=14, calculate K_b(imidazole)/K_b(pyridine) to the nearest integer. JEE Advanced level
Using the pKa values of conjugate acids (anilinium 4.6, methylammonium 10.6, phenol 10.0, acetic acid 4.76, ethanol 15.9), which of the following reactions in a... JEE Advanced level
Which of the following statements about imidazole (pKaH 7.0) and pyridine (pKaH 5.2) are correct? JEE Advanced level
An ether solution contains aniline, benzoic acid (pKa 4.20), phenol (pKa 10.0) and toluene. Using pKaH of anilinium 4.6 and pKa of H2CO3 6.4, which statements a... JEE Advanced level
At pH 7.4 which of the following bases exist mostly (more than 50%) in their protonated form? (pKaH values: methylamine 10.6, aniline 4.6, pyridine 5.2, imidazo... JEE Advanced level
Which statements about the following anions are correct? (pKa of conjugate acids: ethane about 50, ethene about 44, ethyne 25, ammonia 38, water 15.7) JEE Advanced level