300+ REAL TIME Organic Chemistry Objective Questions & Answers 2023

Organic Chemistry Multiple Choice Questions on “Esters”.

1. Which of the following compounds is an ester?
a)
b)
c)
d)
Answer: c
Clarification: Esters are characterized by their possession of a modified carboxyl group, in which the H of the -OH group is replaced by an alkyl group, to form the general functional group -COOR.

2. Which of the following is used as catalyst for the esterification of carboxylic acid and alcohol?
a) Nitrous acid
b) Sulphuric acid
c) Sulphurous acid
d) Nitric acid
Answer: b
Clarification: The classic synthesis is the Fischer esterification, which involves treating a carboxylic acid with an alcohol in the presence of a dehydrating agent:
RCO₂H + R′OH ⇌ RCO₂R′ + H₂O
The equilibrium constant for such reactions is about 5 for typical esters, e.g., ethyl acetate. The reaction is slow in the absence of a catalyst. Sulfuric acid is a typical catalyst for this reaction.

3. What will be the product for the given reaction?
CH₃OH + CO →?
a) Ethyl formate
b) Methyl formate
c) Ethyl acetate
d) Methyl acetate
Answer: b
Clarification: The carbonylation of methanol yields methyl formate, which is the main commercial source of formic acid.
CH₃OH + CO → CH₃O₂CH

4. Hydrolysis of ester leads to the formation of which of the following products in basic medium?
a) Ether and alcohol
b) Alcohol and sodium carboxylate
c) Aldehyde and alcohol
d) Sodium carboxylate
Answer: b
Clarification: Under basic conditions, hydroxide acts as a nucleophile, while an alkoxide is the leaving group.

5. What will be the product for the given reaction?
C₂H₄ + CH₃CO₂H + 1⁄2 O₂ →?
a) Ethyl formate
b) Vinyl formate
c) Ethyl acetate
d) Methyl acetate
Answer: b
Clarification: In the presence of palladium-based catalysts, ethylene, acetic acid, and oxygen react to give vinyl acetate:
C₂H₄ + CH₃CO₂H + 1⁄2 O₂ → C₂H₃O₂CCH₃ + H₂O

6. What is the characteristic smell for ester?
a) Fruity like smell
b) Fish like smell
c) Rotten egg smell
d) Alcoholic smell
Answer: a
Clarification: Many esters have distinctive fruit-like odors, and many occur naturally in the essential oils of plants. This has also led to their commonplace use in artificial flavorings and fragrances when those odors aim to be mimicked.

7. Salts of carboxylate anions can be alkylating agent with alkyl halides to give esters. In the case that an alkyl chloride is used, an iodide salt can catalyze the reaction. What is the name reaction for the given reaction?
a) Favorskii rearrangement
b) Baeyer–Villiger oxidation
c) Pinner reaction
d) Finkelstein reaction
Answer: d
Clarification: Salts of carboxylate anions can be alkylating agent with alkyl halides to give esters. In the case that an alkyl chloride is used, an iodide salt can catalyze the reaction this reaction is known as Finkelstien reaction.

8. What will be the product of given reaction?

a) Ether and alcohol
b) Alcohol and sodium carboxylate
c) Aldehyde and alcohol
d) Carboxylic acid and alkene
Answer: d
Clarification: Ester pyrolysis in is a vacuum pyrolysis reaction converting esters containing a β-hydrogen atom into the corresponding carboxylic acid and the alkene.

Organic Chemistry Multiple Choice Questions on “Stereoisomers”.

1. What is the complete IUPAC name of the following substance?

a) (1S,3S)-1-methylcyclopentane-1,3-diol
b) (1R,3R)-1-methylcyclopentane-1,3-diol
c) (1S,3R)-1-methylcyclopentane-1,3-diol
d) (1R,3S)-1-methylcyclopentane-1,3-diol
Answer: d
Clarification: The IUPAC name will be (1R,3S)-1-methylcyclopentane-1,3-diol, where 1 position shows R and 3 position shows S.

2. How many stereoisomers are there for the following structure?

a) 1
b) 2
c) 3
d) 4
Answer: c
Clarification: In the case of 2,3-dihydroxybutanedioic acid, known as tartaric acid, the two chiral centers have the same four substituents and are equivalent. As a result, two of the four possible stereoisomers of this compound are identical due to a plane of symmetry, so there are only three stereoisomeric tartaric acids.

3. How many stereoisomers of 3-bromo-2-butanol, CH₃CH(OH)CHBrCH₃, exist?
a) 3
b) 1
c) 2
d) 4
Answer: d
Clarification: 3-Bromo-2-butanol has two chirality centers with different sets of four substituents. Each chirality center can have either an S or R configuration. For a compound with n chirality centers there is the possibility of a maximum of 2n stereoisomers. In this case there is more than one stereoisomer.

4. How many stereoisomers of 2,3-butanediol, CH₃CH(OH)CH(OH)CH₃, exist?
a) 3
b) 4
c) 1
d) 2
Answer: a
Clarification: 2,3-Butanediol has two chirality centers but the sets of four substituents on each chirality center are identical. Each chirality center can have either an S or R configuration. The (2R,3R) and (2S,3S) compounds are enantiomers of one another, but the structures drawn as (2R,3S) and (2S,3R) compounds are identical (this is the achiral meso compound), so there are only three different stereoisomers. For a compound with n chirality centers there is the possibility of a maximum of 2n stereoisomers. However, if the sets of four substituents on each chirality center are identical there will be fewer than 2n stereoisomers.

5. What is the complete IUPAC name of the following stereoisomer?

a) (1S)-2-ethyl-3,3-dimethylcyclopentane
b) (1R)-2-ethyl-3,3-dimethylcyclopentane
c) (1S)-1-ethyl-,3,3-diimethylcyclopentane
d) (1S)-3-ethyl-1,1-diimethylcyclopentane
Answer: c
Clarification: The IUPAC name will be (1S)-1-ethyl-,3,3-diimethylcyclopentane, where at 1 position it is S.

6. Which of the following structures represent the same stereoisomer?

a) Only 1 and 2
b) Only 2 and 3
c) 1, 2 and 3
d) Only 3 and 1
Answer: b
Clarification: It is important that you can rotate around carbon-carbon single bonds to make different conformations, and to rotate molecules in three-dimensions to compare their chirality chemistry (model kits are often useful). Another way to determine which of these structures are identical is to determine the configuration of each chirality center. In this case, for each chirality center the priority of the substituents is -Cl >; -CHClCH₃ >; -CH₃ >; -H. For example, the configurations of the chirality centers of compound 1 are both S. However, 1 and 3 are not identical.

7. Which of the following compounds can exhibit geometrical isomerism?
a) 1-Hexene
b) 2-Methyl-2-Pentene
c) 3-methyl-1-pentene
d) 2-Hexene
Answer: d
Clarification: There are several isomers of hexene, depending on the position and geometry of the double bond in the chain. One of the most common industrially useful isomers is 1-hexene an alpha-olefin.

8. How many number of stereoisomers possible for 2, 3-pentanediol?
a) 3
b) 4
c) 5
d) 6
Answer: b
Clarification: 2, 3-pentanediol contains two chiral atoms. So, the number of possible stereoisomers is 4 (22).

9. How many chiral stereoisomers can be drawn for CH₃CHFCHFCH(CH₃)₂?
a) 4
b) 5
c) 6
d) 7
Answer: a
Clarification: CH₃CHFCHFCH(CH₃)₂ contains 2 chiral atoms. So, the number of possible stereoisomers is 4 (2²).

10. What is the total number of isomers, stereoisomers included, designated by the dichlorocyclopentane?
a) 7
b) 6
c) 4
d) 5
Answer: a
Clarification: 3 structural isomers, but if you are considering chirality/diastereomers, there are two chiral carbons, so the maximum number of stereoisomers is 22=4, from which cis-1,2-dichlorocyclopentane and cis-1,3-dichlorocyclopentane will have same structure in their individual 4 isomers as shown below, so total isomers will be 7.

Organic Chemistry Multiple Choice Questions on “Copolymerisation”.

1. Which of the following is true about copolymerisation?
a) radical, coordination, anionic, or cationic polymerization, depending on the type of initiation
b) addition of monomer to a metal complex, propagation is by successive insertion of monomer at the metal, and termination occurs when the metal complex separates from the polymer
c) monomers react by eliminating small molecules like H₂O, NH₃, CH₂O and NaCl in a repetitive manner, Indefinite growth of the polymer occurs at both ends
d) a mixture of more than one (or different) monomeric species is allowed to polymerize
Answer: d
Clarification: When two or more different monomers unite together to polymerize, the product is called a copolymer and the process is called copolymerization. If M and N are present together, Random type MM MN NNN MM N M MM N N…… and Alternating type M N M N M N M N M ………

2. Gradient copolymer comers under which of the following copolymer category?
a) Linked copolymer
b) Branched copolymer
c) Terepolymer
d) Brush copolymer
Answer: a
Clarification: Linear copolymers consist of a single main chain and gradient copolymers are single chain of polymer in which the monomer composition changes gradually along the chain.

3. Which of the following copolymers is the copolymer with regular alternating A and B units?
a) Alternating copolymer
b) Periodic copolymer
c) Statistical copolymer
d) Block copolymer
Answer: a
Clarification: Alternating copolymers are with regular alternating A and B units, as shown below. This sequence will not change.
—- A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B—-

4. Which of the following copolymers is the copolymer with A and B units arranged in a repeating sequence?
a) Alternating copolymer
b) Periodic copolymer
c) Statistical copolymer
d) Block copolymer
Answer: b
Clarification: Copolymers with A and B units arranged in a repeating sequence are periodic polymers as shown below. This sequence will repeat itself to form a polymer.
(A-B-A-B-B-A-A-A-A-B-B-B)_n

5. Which of the following copolymers is the copolymer with sequence of monomer residues follows a statistical rule?
a) Alternating copolymer
b) Periodic copolymer
c) Statistical copolymer
d) Block copolymer
Answer: c
Clarification: Copolymers with sequence of monomer residues follows a statistical rule, are called as statistical copolymer, as shown in below. This sequence will not change.

—- A-B-B-B-A-B-A-B-A-B-A-A-B-B-B-A-A-B—-

6. Which of the following copolymers is the copolymer which comprises two or more homopolymer subunits linked by covalent bonds?
a) Alternating copolymer
b) Periodic copolymer
c) Statistical copolymer
d) Block copolymer
Answer: d
Clarification: Copolymers which comprises two or more homopolymer subunits linked by covalent bonds, are called as block copolymer, as shown in below. This sequence will not change.

—- B-B-B-B-B-A-A-A-A-A-B-B-B-B-B—-

Organic Chemistry Interview Questions and Answers on “Structure and Physical Properties”.

1. Name the geometry of the central oxygen atom in the ozone molecule (O₃).
a) Trigonal planar
b) Linear
c) Tetrahedral
d) Pyramidal
Answer: a
Clarification: It forms a single bond with one oxygen atom, double bond with another oxygen atom and there exists one more non-bonded atom. Thus, it forms a trigonal planar structure.

2. In which molecule there is a complete linear arrangement of all atoms?
a) BF₃
b) NH₃
c) CO₂
d) CH₄
Answer: c
Clarification: BF₃ has trigonal planar structure, NH₃ has a trigonal bipyramidal structure, CH₄ has tetragonal structure and hence CO₂ is the one with linear structure.

3. Choose the incorrect option.
a) BrO₄ – tetrahedral
b) PF₃ – pyramidal
c) ClO₄ – tetrahedral
d) BeBr₂ – linear
Answer: b
Clarification: PF₃ has a trigonal pyramidal structure as it has three bonding pairs and one non-bonding pair.

4. Which among the following is not a physical property?
a) Melting point
b) Boiling point
c) Solubility
d) Reactivity
Answer: d
Clarification: Reactivity is a chemical property and it is not a physical property.

5. A crystalline solid possess which one of the following property?
a) Irregularity
b) Non- symmetric
c) Perfect geometric pattern
d) non- stability
Answer: c
Clarification: A crystalline solid is one which possesses perfect geometry, high stability, symmetric and regularly arranged.

6. Melting is process which can be stated by the below statements except?
a) Change from a highly disordered stated to an ordered state
b) Change from particles in crystal lattice to liquid state
c) Thermal energy of particles overcome the intercrystalline forces that hold them
d) Change from low temperature to high temperature
Answer: a
Clarification: Melting is a process which proceeds by changing from a highly ordered state to a disordered state.

7. Which among the following is not associated with intermolecular forces?
a) They hold neutral molecules
b) Non- electrostatic in nature
c) attraction of oppositely charged particles
d) dipole-dipole interaction and van der Waals forces
Answer: b
Clarification: Intermolecular forces are electrostatic in nature.

8. Which among the following statement is not true?
a) In liquid, particles are less regularly arranged and are free to move
b) Boiling involves breaking up of group of molecules in liquid
c) Boiling involves clubbing of oppositely charged ions
d) Thermal energy of particles overcome cohesive forces that hold them
Answer: c
Clarification: Boiling involves separation of oppositely charged ions and makes them as individual ions.

9. When one of the Hydrogen in Methane(CH₄) is replaced by a hydroxyl group, then structurally methane resembles?
a) Methanol
b) Ethanol
c) Water
d) Both methanol and water
Answer: d
Clarification: Like water, it is a liquid with boiling point which is abnormally high for a compound of its size and polarity.

10. Which among the following does not match with the term solubility?
a) The structural units get separated from each other
b) The ion-dipole bond is very strong
c) The spaces in between the structures are occupied by solvent molecules
d) The electrostatic attraction between the oppositely charged ions and their corresponding ends are called ion-dipole bond
Answer: b
Clarification: The bond is weak but in the aggregate they supply enough energy to overcome the interionic forces.

Organic Chemistry for Interviews,

Organic Chemistry Multiple Choice Questions on “Aromatic Hydrocarbons”.

1. Identify the correct statement which is related to aromatic hydrocarbon?
a) It has only sigma bonds
b) It has only pi bonds
c) It has a sigma and two pi bonds
d) It has a sigma and delocalized pi bond
Answer: d
Clarification: An aromatic hydrocarbon always has a sigma as well as a delocalized pi bond found between the carbon atoms.

2. Select the incorrect option.
a) The aromatic hydrocarbon has a pleasant aroma (smell)
b) Some of the aromatic compounds are ring-shaped
c) Aromatic hydrocarbon can be either mono or polycyclic
d) Benzene is the simplest hydrocarbon
Answer: b
Clarification: All the aromatic hydrocarbon are ring shaped as all of them are sp2 hybridized with a geometry of trigonal planar.

3. Which among the following is not a property of aromatic hydrocarbon?
a) These compounds have very good aromaticity
b) These compounds have excellent stability
c) These compounds do not undergo nucleophilic substitutions but they undergo electrophilic substitutions
d) There exists a strong ratio between carbon and hydrogen
Answer: c
Clarification: Aromatic hydrocarbons undergo both electrophilic and nucleophilic aromatic substitutions.

4. Arenes does not undergo ___________
a) Dehydrogenation
b) Coupling reaction
c) Halogenation
d) Cyclo additions
Answer: a
Clarification: Arenes undergo hydrogenation reaction and form saturated ring products.

5. Which among these is not a representative arene compound?
a) Durene
b) Picric chloride
c) Aspirin
d) Mesitylene
Answer: b
Clarification: Picric acid is a representative arene compound but not picric chloride.

6. Which among these is the simplest example for polycyclic arenes?
a) Benzacephenanthrylene
b) Naphthalene
c) Pyrene
d) Dibenz-anthracene
Answer: b
Clarification: Naphthalene has fused ring of aromaticity and has the simplest structure when compared with other polycyclic aromatic hydrocarbons.

7. Arenes are polar.
a) True
b) False
Answer: b
Clarification: Arenes are insoluble in water and hence they are non polar compounds.

8. Arenes are _________
a) volatile
b) Water soluble
c) Non-carcinogenic
d) Mostly gases
Answer: a
Clarification: Arenes have a very low boiling point and hence they are volatile in nature.

9. The main sources of these arenes are _________
a) Petroleum
b) Biogas and petroleum
c) Petroleum and coal tar
d) Natural gas
Answer: c
Clarification: As these petroleum and natural gas comprise of naturally occurring compounds such as carbon and hydrogen in abundance, these serve as the main source of arenes.

10. Benzene has a stronger Vander-Waal’s force than Methylbenzene.
a) False
b) True
Answer: a
Clarification: The benzene molecule is smaller than that of the methylbenzene and hence it does not have the Vander-Waal’s forces as equal to those of methylbenzene.

Organic Chemistry Multiple Choice Questions on “Photochemistry”.

1. The fact that the fluorescence wavelength is often much longer than the irradiation wavelength (Stokes shift) is a consequence of which phenomenon?
a) low extinction coefficients (Lambert-Beer law)
b) vertical transitions (Kasha’s rule)
c) high ISC rates (El Sayed rule)
d) the Franck–Condon principle
Answer: d
Clarification: The reason why Stokes shifts occur is the Franck–Condon principle, which states that a change in the electronic state of some molecule caused by the absorption of a photon occurs so rapidly that the motion of the nuclear coordinates during the transition can be neglected. After the electronic transition is complete, the molecule’s nuclear coordinates then relax into a lower-energy configuration in response to the change in the electronic wave function.

2. Which of the following is an incorrect statement?
a) First step in photochemistry is excited state (photoexcitation)
b) Photochemical reactions are caused by absorption of ultraviolet only
c) When a molecule or atom in the ground state (S₀) absorbs light, one electron is excited to a higher orbital level
d) It is possible for the excited state S₁ to undergo spin inversion
Answer: b
Clarification: Photochemical reactions are caused by absorption of ultraviolet, (wavelength from 100 to 400 nm), visible light (400 – 750 nm) or infrared radiation (750 – 2500 nm).

3. Which regions of the light radiations of the visible ultraviolet lying between – wavelength are chiefly concerned in bringing about photochemical reactions?
a) 1000 Å and 2000 Å
b) 1500 Å and 1000 Å
c) 8000 Å and 2000 Å
d) 19000 Å and 12,000 Å
Answer: c
Clarification: The region of interest for photochemistry is between 8000 Å and 2000 Å of visible and ultraviolet (UV), are only a small part of the full electromagnetic spectrum. Longer wavelengths, e.g., far infrared, tend to cause the vibrational excitation of molecules, which results in heating. Shorter wavelength X-rays cause ionization.

4. Which of the following instruments is used to measure the energy of the monochromatic radiation most accurately?
a) Photoelectric cell
b) Thermopile
c) The potential detector
d) The chemical actinometer
Answer: b
Clarification: A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel.

5. The molar extinction coefficient of B (MW = 180) is 4 x 10³ L mol^-1 cm^-1. One-liter solution of C which contains 0.1358 g pharmaceutical preparation of B, shows an absorbance of 0.411 in a 1 cm quartz cell. What is the percentage (w/w) of B in the pharmaceutical preparation?
a) 10.20
b) 13.60
c) 20.40
d) 29.12
Answer: b
Clarification:

6. What are the appropriate reasons for the deviation from the Beer’s law among the following?

(A) Monochromaticity of light 
(B) Very high concentration of analyte
(C) Association of analyte 
(D) Dissociation of analyte

a) A, B and D
b) B, C and D
c) A, C and D
d) A, B and C
Answer: b
Clarification: Reasons for derivation from Beer’s law are very high concentration of analyte, Association or Dissociation of analyte and Refractive index → Polychromatic light. Monochromaticity of light don’t have any effect on Beer’s law.

7. A 0.1 M solution of compound A shows 50% transmittance when a cell of 1 cm width is used at λ₁ nm. Another 0.1 M solution of compound B gives the optical density value of 0.1761 using 1cm cell at λ₁ nm. What will be the transmittance of a solution that is simultaneously 0.1 M in A and 0.1 M in B using the same cell and at the same wave length? [log 1.301; log 1.4771; log 50 = 1.699].
a) 33.3%
b) 50%
c) 66.7%
d) 70%
Answer: a
Clarification: Case I: Transmittance (T1) = 50% = ⁵⁰⁄₁₀₀ = ¹⁄₂
Case II: Optical density or Absorbance = 0.17610
A₂ = 0.1761
T₂ = 10^-A2 = 10^-0.1761 = 0.67.
∴ Net Transmittance ‘T’ = T1 × T2 = ¹⁄₂ × 0.67 = 0.33 = 33%.

8. Which of the following will result in deviation from Beer’s law?

(A) Change in a refractive index of medium 
(B) Dissociation of analyte on dilution
(C) Polychromatic light                                  
(D) Path length of cuvette

a) A, B and C
b) B, C and D
c) A, C and D
d) A, B and D
Answer: a
Clarification: Change in a refractive index of medium, Dissociation of analyte on dilution and Polychromatic light (reflective index) will result in deviation from Beer’s law.

9. The quantum efficiency of a photochemical reaction is defined as _______
a) ratio of molecules decomposed in a given time to the number of quanta absorbed in the same time
b) number of 11101ecules decomposed in a given time
c) number or quanta absorbed percent time
d) ratio of’ molecules decomposed in a given time to the number of quanta emitted in the same time
Answer: a
Clarification: According to the definition ratio of molecules decomposed in a given time to the number of quanta absorbed at the same time is the correct option.

10. Which of the following are the reactions in which molecules absorbing light do not themselves react but induce other molecules to react?
a) Free radical reactions
b) Chain reactions
c) Reversible reactions
d) Photosensitized reactions
Answer: d
Clarification: Photosensitized reactions is the reactions in which molecules absorbing light do not themselves react but induce other molecules to react.

11. A substance absorbs 2.0 x 10¹⁶ quanta or radiations per second and 0.002 mole of it reacts in 1200 seconds. What is the quantum yield or the reaction (N = 6.02 x 10²³)?
a) 50
b) 40
c) 80
d) 100
Answer: a
Clarification: No. of quanta of radiations absorbed in 1200 seconds = 2 × 10¹⁶ × 1200

Category: Organic Chemistry Objective Questions

250+ TOP MCQs on Esters and Answers

250+ TOP MCQs on Stereoisomers and Answers

250+ TOP MCQs on Copolymerisation and Answers

250+ TOP MCQs on Structure and Physical Properties and Answers

250+ TOP MCQs on Aromatic Hydrocarbons and Answers

250+ TOP MCQs on Photochemistry and Answers