300+ REAL TIME Organic Chemistry Objective Questions & Answers 2023

250+ TOP MCQs on Electrophilic Substitution in Pyridine and Answers

Organic Chemistry Assessment Questions and Answers on “Electrophilic Substitution in Pyridine”.

1. Electrophilic substitution reaction of pyridine is most effective in which of the conditions?
a) In slightly acidic conditions
b) In slightly basic conditions
c) In neutral medium
d) In vigorous conditions
Answer: d
Clarification: When electrophilic substitution reaction of pyridine is carried out in acidic conditions then pyridine ring will further get deactivated forming pyridinium ion. However, under more vigorous conditions the usual electrophilic substitution reaction can be possible but yield will be less.

2. Which of the following electrophilic substitution reaction is not possible in pyridine?
a) Nitration
b) Sulphonation
c) Bromination
d) Friedel craft reaction
Answer: d
Clarification: Common alkylations and acylations, such as Friedel–Crafts alkylation or acylation, usually fail for pyridine because they lead only to the addition at the nitrogen atom. Substitutions usually occur at the 3-position, which is the most electron-rich carbon atom in the ring and is, therefore, more susceptible to an electrophilic addition.

3. At which position of pyridine electrophilic substitution reaction is most preferred?
a) First
b) Second
c) Third
d) Forth
Answer: c
Clarification: Electrophilic substitution reaction at position the 3-position is preferred over attack at 2 and 4-position because the intermediate found by electrophilic addition at 3-position is more stable as it will have 3-resonating structure and none of will have positive charge on N.

4. Which of the following is the product for the below reaction?

a) 3- Nitropyridine
b) 2- Nitropyridine
c) 4- Nitropyridine
d) 2,4- dinitropyridine
Answer: a
Clarification: Electrophilic substitution reaction at position the 3-position is preferred over attack at 2 and 4-position because the intermediate found by electrophilic addition at 3-position is more stable as it will have 3-resonating structure and none of will have positive charge on N.

5. Which of the following is the product for the below reaction?

a) 3- bromopyridine
b) 2- bromopyridine
c) 2- bromopyridine and 3- bromopyridine
d) 3- bromopyridine and 3,5- dibromo pyridine
Answer: d
Clarification: Electrophilic substitution reaction at position the 3-position 5 position is preferred over attack at 2 and 4-position because the intermediate found by electrophilic addition at 3-position is more stable as it will have 3-resonating structure and none of will have positive charge on N.

6. Which of the following is the product for the below reaction?

a) 3- pyridinesulphonic acid
b) 2- pyridinesulphonic acid
c) 4- pyridinesulphonic acid
d) 2,4- pyridinedisulphonic acid
Answer: a
Clarification: Electrophilic substitution reaction at position the 3-position is preferred over attack at 2 and 4-position because the intermediate found by electrophilic addition at 3-position is more stable as it will have 3-resonating structure and none of will have positive charge on N.

7. Which of the following is the product for the below reaction?

a) 3- methyl-pyridine-5-sulphonic acid
b) 3- methyl-pyridine-4-sulphonic acid
c) 3- methyl-pyridine-6-sulphonic acid
d) 3- methyl-pyridine-1-sulphonic acid
Answer: a
Clarification: Alkyl group activate the pyridine ring towards electrophilic substitution, however, directive influence of the ring predominates regardless of the position of alkylation i.e. attack at 3-position.

8. Which of the following is the product for the below reaction?

a) 5- bromo-2-aminopyridine
b) 3- bromo-2-aminopyridine
c) 4- bromo-2-aminopyridine
d) 6- bromo-2-aminopyridine
Answer: a
Clarification: Amino group dominates the ring orientation effect and direct the incoming electrophile to o- and p- position. 2-amino group directs the incoming electrophile predominantly to the 5-position.

9. Which of the following is the product for the below reaction?

a) 2- Nitro-3-aminopyridine
b) 4- Nitro-3-aminopyridine
c) 5- Nitro-3-aminopyridine
d) 6- Nitro-3-aminopyridine
Answer: a
Clarification: Amino group dominates the ring orientation effect and direct the incoming electrophile to o- and p- position. 3-amino group directs the incoming electrophile predominantly to the 2-position.

10. Which of the following is the product for the below reaction?

a) 4-amino -pyridine-5-sulphonic acid
b) 4- amino -pyridine-3-sulphonic acid
c) 4- amino -pyridine-6-sulphonic acid
d) 4- amino -pyridine-2-sulphonic acid
Answer: a
Clarification: Amino group dominates the ring orientation effect and direct the incoming electrophile to o^– and p^– position. 4-amino group directs the incoming electrophile predominantly to the 3-position.

Organic Chemistry Assessment Questions,

250+ TOP MCQs on Quantitative and Qualitative Analysis and Answers

Organic Chemistry Interview Questions and Answers for freshers on “Quantitative and Qualitative Analysis”.

1. Identify the one which does not come under the chemical methods of quantitative analysis?
a) Gravimetric
b) Titrimetric
c) Volumetric
d) Magnetic suceptibility
Answer: d
Clarification: Magnetic suceptibility comes under physical methods of qunatitative analysis and hence the answer.

2. Quantitative analysis is one which is used for separating out the specific constituents from a mixture.
a) True
b) False
Answer: b
Clarification: Quantitative analysis is used to measure the quantity, (i.e the amount) present and the above mentioned statement defines qualitative analysis.

3. Select the incorrect statement regarding analytical balance.
a) It is the fundamental kit in quantitative analysis
b) It measures samples very accurately
c) It could measure the difference in mass upto 0.1 mg
d) It is not a sensitive instrument
Answer: d
Clarification: It is a very sensitive instrument as it could accurately measure the weight of a particular compound of upto 0.1 mg.

4. Which among the following is not a physical method?
a) X-ray fluorescence spectroscopy
b) Atomic emission spectroscopy
c) Inert gas fusion
d) Trace element analysis
Answer: c
Clarification: Inert gas fusion is an example of chemical methods of quantitative analysis, as it involves chemical reaction such as oxidation.

5. Select the inappropriate statement regarding quantitative analysis.
a) It helps in determining the outcome of the product
b) It helps in determining the impurities in the sample
c) It fails to indicate the presence of lead in some compound
d) It could identify the amounts of dosage present in the drug
Answer: c
Clarification: It can identify the presence of lead and could also account for its concentration in case of paints and toys.

6. Identify the test which is not a part of qualitative analysis?
a) Litmus test
b) Kastle-Meyer test
c) Iodine test
d) Flame test
Answer: a
Clarification: Kastle-meyer test is done for identification of blood, Iodine test is done for identification of starch and Flame test is done to identify Barium.

7. Covalent molecules can be identified using quantitative methods.
a) False
b) True
Answer: a
Clarification: The qualitative analysis is used to identify covalent molecules by distinguishing them using physical properties such as melting point, etc.

8. Identify the reagent which is not commonly used in qualitative analysis?
a) 6M NaOH
b) 6M HCl
c) 6M HNO₃
d) 6M NH₄
Answer: d
Clarification: 6M NH₃ is the reagent commonly used in qualitative analysis because it is used in almost every group procedures.

9. Select the correct statement about the reagent 6M HNO₃.
a) It forms hydroxo complexes
b) It destroys hydroxo and ammonia complexes
c) It forms NH₃ complexes
d) It decreases the H+ ion concentration
Answer: b
Clarification: It is a good oxidizing agent, dissolves in insoluble hydroxides and it destroys hydroxo and ammonia complexes.

10. Identify the incorrect statement regarding the reagent 6M NH₃.
a) It increases hydroxide and NH₃ concentration
b) It decreases H+ concentration
c) It is capable of precipitating insoluble hydroxides
d) It is capable of forming hydro complexes
Answer: d
Clarification: It forms only NH₃ complexes and does not form hydro complexes.

Organic Chemistry for Interviews,

250+ TOP MCQs on UV – Visible Spectroscopy and Answers

Organic Chemistry Multiple Choice Questions on “UV – Visible Spectroscopy”.

1. What is the wavelength range for UV spectrum of light?
a) 400 nm – 700 nm
b) 700 nm to 1 mm
c) 0.01 nm to 10 nm
d) 10 nm to 400 nm

Answer: d
Clarification: Ultraviolet (UV) is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays (the visible region fall between 380-750 nm and X- rays region fall between 0.01 to 10nm).

2. Which of the following comparison is correct for solvent shift on the n –>π* transition of acetone?
a) H₂0 = CH₃0H = C₂H₅0H = CHC1₃ = C₆H₁₄
b) H₂0 > CH₃0H > C₂H₅0H > CHC1₃ > C₆H₁₄
c) H₂0 < CH₃0H < C₂H₅0H < CHC1₃ < C₆H₁₄
d) H₂0 > CH₃0H < C₂H₅0H < CHC1₃ < C₆H₁₄
Answer: c
Clarification: H-bonding with ground state in n–> π* results in increase in energy gap & decrease in wavelength.
And as polar solvents show strong H-bonding. So, the correct option is H₂0 ₃0H ₂H₅0H ₃₆H₁₄.

3. What is the correct order of λmax for n –> σ* transition?
a) R-OH > R-NH₂ > R-SH
b) R-OH < R-NH₂ < R-SH
c) R-OH > R-SH > R-NH₂
d) R-OH < R-SH < R-NH₂
Answer: b
Clarification: According to molecular orbital energy diagram for R-OH, R-NH₂, R-SH (shown below), energy level will decrease respectively so λmax will increase.

4. What is the correct order of λmax for n –> π* transition for the R-CN, R-NO₂, and R-N=N-R?
a) R-CN < R-NO₂ < R-N=N-R
b) R-CN = R-NO₂ = R-N=N-R
c) R-CN > R-NO₂ > R-N=N-R
d) R-CN > R-NO₂ < R-N=N-R
Answer: a

5. What is the correct order of λ_max for π –> π* transition for the following three compounds?
a) R-C=C-R > R₂C = CR₂ > R-CHO
b) R-C=C-R < R₂C = CR₂ < R-CHO
c) R-C=C-R = R₂C = CR₂ = R-CHO
d) R-C=C-R < R₂C = CR₂ >R-CHO

Answer: b
Clarification: MO diagram (C = C), (C = C) & (C = O) and shows the energy gap between π – π*, increases among these three molecules. So λ_max will give the reverse trend.
R-C=C-R < R₂C = CR₂ < R-CHO

6. What is the correct order of λ_max for n–> π* transition for the following three compounds?
a) RCOOH > RCOOR’ > RCONH₂
b) RCOOH = RCOOR’ = RCONH₂
c) RCOOH = RCOOR’ < RCONH₂
d) RCOOH = RCOOR’ > RCONH₂
Answer: b

7. Which of the following is the correct order of λ_max for n–> π* transition for the given compounds?
a) 1>2>3>4>5
b) 1<2<3<4<5
c) 1>2<3>4<5
d) 1>2>3<4>5

Answer: a
Clarification: λ_max depends upon +m & I effect, which will lead to a shift to longer wavelength accompanied by increased intensity of absorption represents an electronic level (considering inductive and mesomeric effect) of the ground and excited states and thus a decrease in transition energy.
The correct order of λ_max is 1 > 2 > 3 > 4 > 5.

8. The ultraviolet spectrum of benzonitrile shows a primary absorption band at 224 nm. If a solution of benzonitrile in water, with a concentration of 1x 10^-4 molar, is examined at a wavelength of 224 nm, the absorbance is determined to be 1.30. The cell length is 1 cm. What is the molar absorptivity of this absorption band?
a) 2.3 x 10⁴
b) 3.3 x 10⁴
c) 1.3 x 10⁴
d) 4.3 x 10⁴

Answer: c
Clarification:
Benzonitrile in water with:
C = 1 x 10^-4 M
A = 1.30
l = 1 cm
We know, A = ℇCl
ℇ = A/C I = 1.30/ 1X 10^-4 X 1 = 1.34 X 10⁴.

9. The ultraviolet spectrum of benzonitrile shows a secondary absorption band at 271 nm. If a solution of benzonitrile in water, with a concentration of 1×10^-4 molar solution is examined at 271 nm, what will be the absorbance reading (ℇ = 1000) and what will be the intensity ratio, I_O/I, respectively?
a) 0.1, 1.26
b) 0.2, 2.26
c) 0.3, 3.26
d) 0.4, 4.26

Answer: a
Clarification: A = ℇCl and ℇ = 1000 (Given)
A = 1000 x 1 x10^-4 x 1
A = 0.1
Also, A = log (I_O/l)
0.1 = log (I_O/I)
=> I_O/I = 1.26.

250+ TOP MCQs on Aryl Halides and Answers

Organic Chemistry Multiple Choice Questions on “Aryl Halides”.

1. Dehydrohalogenation of 1,2 di-bromo cyclohexane gives which of the following compound?
a)
b)
c)
d)
Answer: a
Clarification: As we can see in below reaction that double E2 elimination yields the conjugated diene, 1,3-cyclohexadiene. Note the overall transformation is alkene to conjugated diene.

2. Which one of the following possess highest melting point?
a) Chlorobenzene
b) o-dichlorobenzene
c) m-dichlorobenzene
d) p-dichlorobenzene
Answer: d
Clarification: p-dichlorobenzene molecule has symmetrical structure. It can fit well in its crystal lattice. The intermolecular forces of attraction are strong. Hence, it possesses highest melting point.

3. What would be the product formed for the following reaction?
a)
b)
c)
d)
Answer: d
Clarification: When 1-Bromo-3-chloro cyclobutane reacts with two equivalents of metallic sodium in ether it is the example of Wurtz reaction.

4. Which of these can be used as moth repellent?
a) Benzene hexachloride
b) Benzal chloride
c) Hexachloroethane
d) Tetrachloroethane
Answer: c
Clarification: Hexachloroethane can be used as moth repellent. It has also been used as a plasticizer for cellulose esters in place of camphor, a polymer additive, a component of fungicidal and insecticidal formulations, in the formulation of extreme pressure lubricants, and in the manufacture of fire extinguishing fluids.

5. What will be the product for the following reaction?

a)
b)
c)
d)
Answer: a
Clarification: −CCl₃ is a m-directing group. So, attack will be at meta position.

6. Which of the following is true about chlorobenzene?
a) Chlorobenzene is less reactive than benzyl chloride
b) Chlorobenzene is more reactive than ethyl bromide
c) Chlorobenzene is nearly as reactive as methyl chloride
d) Chlorobenzene is more reactive than isopropyl chloride
Answer: a
Clarification: Chlorobenzene is less reactive than benzyl chloride. In chlorobenzene the lone pairs present on Cl atom get involved in resonance with π electrons of benzene due to which C−Cl bond acquires double bond character Hence, reactivity decreases. C₂H₅−Cl is more reactive than C₆H₅−CH₂−Cl.

7. In the below process what is the product A?

a) Fluorobenzene
b) Benzene
c) 1, 4-difluorobenzene
d) 1, 3-difluorobenzene
Answer: a
Clarification: In this reaction aniline is to be treated with nitrous acid to form benzene diazonium chloride, which is further reacted with HBF₄ to form benzene diazonium fluorobarate. This is when heated, undergoes decomposition to give fluorobenzene. This reaction is called as Balz-Shiemann reaction.

8. What is the name of the following reaction?

a) Chlorination
b) Sandmeyer’s reaction
c) Perkin reaction
d) Substitution reaction
Answer: b
Clarification: The substitution of an aromatic amino group is possible via preparation of its diazonium salt and subsequent displacement with a nucleophile (Cl^–, I^–, CN^–, RS^–, HO^–) is known as Sandmeyer’s reaction.

9. Which of the following is the commercial method of preparation of Chlorobenzene?
a) Raschig process
b) Wurtz Fitting reaction
c) Friedel-Crafts reaction
d) Grignard reaction
Answer: a
Clarification: An industrial process for making chlorobenzene (and phenol) by a gas-phase reaction between benzene vapour, hydrogen chloride, and oxygen (air) at 230°C. The catalyst is copper(II) chloride.
2C₆H₆ + 2HCl + O₂ → 2H₂O + 2C₆H₅Cl

10. Benzene reacts with chlorine to form benzene hexachloride in presence of which of the following reactant?
a) Nickel
b) AlCl₃
c) Bright sunlight
d) Zinc
Answer: c
Clarification: Benzene will react with three molecules of chlorine in the presence of sunlight to give benzene hexachloride.

Organic Chemistry Objective Questions & Answers on “Physical Properties of Carboxylic Acids”.

1. Which of the following acids has the smallest dissociation constant?
a) CH₃CHFCOOH
b) FCH₂CH₂COOH
c) BrCH₂CH₂COOH
d) CH₃CHBrCOOH
Answer: c
Clarification: BrCH₂CH₂COOH is least acidic or has less Ka i.e., dissociation constant. It is A due to lesser -I effect of Br than F and B Br atom further away form −COOH group.

2. The vapour of a carboxylic acid HA when passed over MnO₂ at 573 K yields propanone. What is the acid HA?
a) Methanoic acid
b) Ethanoic acid
c) Propanoic acid
d) Butanoic acid
Answer: b
Clarification: The vapour of ethanoic acid (HA) when passed over MnO₂ at 573 K yields propanone.

3. Which acid is strongest or Which is most acidic?
a) Cl₂CH.COOH
b) ClCH₂COOH
c) CH₃COOH
d) Cl₃C.COOH
Answer: b
Clarification: Presence of -I effect chlorine atom increases the acidic nature by withdrawing electrons.
Cl₃CCOOH > Cl₂CHCOOH > Cl−CH₂−COOH > CH₃COOH

4. The acid which reduces Fehling solution is which of the following?
a) Methanoic acid
b) Ethanoic acid
c) Butanoic acid
d) Propanoic acid
Answer: a
Clarification: Methanoic acid resemble with aldehyde due to its structure. So, it reduces Fehling reagent.

5. Which class of compounds shows H-bonding even more than in alcohols?
a) Phenols
b) Carboxylic acids
c) Ethers
d) Aldehydes
Answer: b
Clarification: Forms H-bonding by means two highly electronegative atoms present in it.

6. Which of the following is the strongest acid?
a) CH₃COOH
b) BrCH₂COOH
c) ClCH₂COOH
d) FCH₂COOH
Answer: d
Clarification: Presence of -I effect fluorine atom increases the acidic nature by withdrawing electrons.
F−CH₂−COOH > Cl−CH₂−COOH > Br−CH₂−COOH > CH₃COOH.

7. The reaction of HCOOH with conc.H2SO4 gives which of the following compound?
a) CO₂
b) CO
c) Oxalic acid
d) Acetic acid
Answer: b
Clarification: The reaction of HCOOH with conc.H₂SO₄ gives carbon monoxide and water.

Category: Organic Chemistry Objective Questions

250+ TOP MCQs on Electrophilic Substitution in Pyridine and Answers

250+ TOP MCQs on Quantitative and Qualitative Analysis and Answers

250+ TOP MCQs on UV – Visible Spectroscopy and Answers

250+ TOP MCQs on Aryl Halides and Answers

250+ TOP MCQs on Reactions of Glycols and Answers

250+ TOP MCQs on Physical Properties of Carboxylic Acids and Answers