300+ REAL TIME Organic Chemistry Objective Questions & Answers 2023

250+ TOP MCQs on Alkanes and Answers

Organic Chemistry Multiple Choice Questions on “Alkanes”.

1. Select the incorrect statement regarding alkanes.
a) It is otherwise known as Paraffin
b) It is an acyclic saturated hydrocarbon
c) In alkanes, C-C bonds are single
d) Alkanes have the general formula C_nH_2n
Answer: d
Clarification: Alkanes have the general formula C_nH_2n+2, i.e; they have two additional hydrogen atoms in comparison with the others.

2. Identify the simplest alkane.
a) Methane
b) Methene
c) Ethane
d) Ethene
Answer: a
Clarification: Methane, called the parent molecule, is the simplest among the alkanes and it has the simplest formula with one carbon atom.

3. Select the minimum number of carbon atoms, a molecule must possess so as to be regarded as a higher alkane.
a) 15
b) 16
c) 17
d) 18
Answer: c
Clarification: A molecule with more than 17 carbon atoms are regarded as higher alkanes such as waxes and solids.

4. Identify the incorrect statement.
a) Alkanes with repeated –CH₂– units constitute a homologus series
b) They are very reactive
c) They have very less biological activity
d) Petroleum and natural gas are the main sources of alkanes
Answer: b
Clarification: Alkanes in general are not very reactive, but they are associated with functional groups which are reactive.

5. Which among the following is not an alkane isomer with 6 carbon atoms?
a) Hexane
b) 2,3-dimethylbutane
c) 2,2-dimethylbutane
d) Neopentane
Answer: d
Clarification: Neopentane is an isomer with 5 carbon atoms and hence it is not an isomer with 6 carbon atoms.

6. The other name for branched chain alkanes is _____________
a) Paraffins
b) Isoparaffins
c) Neoparaffins
d) Naphthenes
Answer: b
Clarification: Linear and branched chain alkanes have difference in their physical properties and hence they are given different prefix like n- and iso-respectively.

7. Select the incorrect statement regarding the boiling points of alkanes.
a) Boiling point increases with stronger Vander Waal’s forces
b) Surface area is the only factor which determines the boiling point of alkane
c) Boiling point of straight chain alkanes is greater than that of branched chain alkanes
d) The boiling point of cycloalkanes is always higher than that of linear alkanes
Answer: b
Clarification: Number of electrons and surface area are the two factors which determine the boiling point.

8. Choose the correct statement.
a) Alkanes have poor conductivity
b) They form hydrogen bonds
c) They have good solubility in non polar solvents than polar solvents
d) Alkanes have less density than that of water
Answer: b
Clarification: They undergo polarization and hence they do not form hydrogen bonds.

9. Liquified petroleum gas is mainly composed of _____________
a) Methane and ethane
b) Ethane and propane
c) Propane and butane
d) Butane and hexane
Answer: c
Clarification: At low pressure both propane and butane gets liquefied, hence they form the main components of LPG.

10. An alkane with 6 carbon atoms will have how many hydrogen atoms?
a) 11
b) 12
c) 13
d) 14
Answer: d
Clarification: From the formula C_nH_2n+2, if n=6 then (2*6)+2=14.

250+ TOP MCQs on Infrared Spectroscopy and Answers Quiz

Organic Chemistry Multiple Choice Questions on “Infrared Spectroscopy”.

1. What is the relation between restoring force, f to the displacement q in Hooke’s law?
a) f = -kq
b) f = kq
c) f = kq²
d) f = -kq²

Answer: a
Clarification: Restoring force f needed to extend or compress a spring by some distance is proportional to that distance.
needed to extend or compress a spring by some distance is proportional to that distance.

2. The intensity of an absorption band is always proportional to which of the following factor?
a) Atomic population
b) Molecular population of the initial state
c) Molecular population of the final state
d) Temperature

Answer: b
Clarification: The probability of a transition taking place in initial state is the most important factor influencing the intensity of an observed l line. This probability is proportional to the population of the initial state involved in the transition.

3. On which factors the vibrational stretching frequency of diatomic molecule depend?
a) Force constant
b) Atomic population
c) Temperature
d) Magnetic field

Answer: a
Clarification: The value of vibrating stretching frequency is shifted if the force constant of a bond changes with its electronic structure. Frequency shifts also take place on working with the same substance in different states (solids, liquids and gas). A substance usually absorbs at higher frequency in a gaseous state as compared to liquid and solid states.

4. In which unit Force constant is not expressed?
a) Dynes cm^-1
b) dyne Å^-1
c) Nm^-1
d) kp

Answer: d
Clarification: All of the above units are correct for force constant except kp, i.e. kilogram force or kilopond, which is the unit of force.

5. For HCI = 1.63 x 10^-27 kg, the observed frequency = 2890 or v = 8.67 x 10¹³ Hz. What is the force constant K?
a) 4.83 m dyn Å^-1
b) 8.43 dynes cm^-1
c) 483 μm^-1
d) 4.83 dyn Å^-1

Answer: a

6. Since the nuclei in a polyatomic molecule do not always vibrate in a simple harmonic manner, there arises which of the following situation?
a) Harmonicity
b) Anharmonicity in molecular vibrations
c) Fundamental frequencies
d) Infrared

Answer: a

7. The vibrations, without a center of symmetry are active in which of the following region?
a) Infrared but inactive in Raman
b) Raman but inactive in IR
c) Raman and IR
d) Inactive in both Raman and IR

Answer: c
Clarification: If a molecule has COS, then its vibrational mode will either IR active or Raman Active.

8. The frequency of vibration of a bond is a function of which factor?
a) Force constant of the bond
b) Masses of the atoms involved in bonding
c) Force constant of the bond and Masses of the atoms
d) Bond order

Answer: c

9. What is the order of decreasing vibrational frequency for C — Cl, C — Br, C — C, C — O and C — H?
a) C-H, C-C, C-O, C- Cl, C-Br
b) C- Cl, C-Br, C-C, C -H, C-O
c) C-O, C-H, C-Br, C- Cl, C-C
d) C-Br, C- Cl, C-C, C-O, C-H

Answer: a

10. What is the correct increasing order of stretching frequencies for C ≡ C, C = C and C — C?
a) C — C > C = C > C ≡ C
b) C ≡ C > C = C > C — C
c) C — C > C = C < C ≡ C
d) C ≡ C < C — C > C = C

Answer: b
Clarification: Since, v ∝ √k , k→ Force constant. Force constant trend is
Triple bond > Double bond > Single bond.
C ≡ C > C = C > C — C.

250+ TOP MCQs on Polyhalogen Derivatives and Answers

Organic Chemistry Multiple Choice Questions on “Polyhalogen Derivatives”.

1. What will be the product for the given reaction?
a) CCl₃CHO
b) C₆H₆Cl₆
c) C₆H₁₂Cl₆
d) C₆H₉Cl₂
Answer: b
Clarification: Benzyl hexachloride will be formed when Benzene reacts with chlorine in presence of U.V light.
C₆H₆ + 3Cl₂ + U.V light → C₆H₆Cl₆
Benzene BHC

2. The molecular formula of DDT has how many chlorine atoms?
a) 5 chlorine atoms
b) 2 chlorine atoms
c) 3 chlorine atoms
d) 4 chlorine atoms
Answer: a
Clarification: As we can in below molecular structure of DDT has 5 chlorine atoms.

3. What is the IUPAC name of chloroform?
a) Dichloromethane
b) Trichloromethane
c) Chloromethane
d) Carbon tetrachloride
Answer: b
Clarification: Chloroform, or trichloromethane, is an organic compound with formula CHCl₃. It is a colorless, sweet-smelling, dense liquid that is produced on a large scale as a precursor to PTFE.

4. Which among the following is true?
a) Freon does not initiate radical chain reactions in stratosphere
b) Iodoform initiates radical chain reactions in stratosphere
c) Freon initiates radical chain reactions in stratosphere
d) Chloroform initiates radical chain reactions in stratosphere
Answer: c
Clarification: Freon (Eg: CFCl₃– Freon11) does initiate radical chain reactions in stratosphere, which can upset the ozone layer.

5. CF_xCl_y [where x + y = 4], why these compounds are not used?
a) These are fluoro carbons
b) These are difficult to synthesise
c) They deplete ozone layer
d) These are very expensive
Answer: c
Clarification: CFC molecules are made up of chlorine, fluorine and carbon atoms and are extremely stable. This extreme stability allows CFC’s to slowly make their way into the stratosphere (most molecules decompose before they can cross into the stratosphere from the troposphere).

6. Which one of the following is the correct formula of methylene dichloride?
a) ClCH = CHCl
b) ClC ≡ CCl
c) CH₂Cl₂
d) CH₂(Cl) CH₂Cl
Answer: c
Clarification: As we can see below molecular diagram of methylene dichloride the correct molecular formula is CH₂Cl₂.

7. Central nervous system can be depressed by the use of which of the following?
a) Chloroform
b) Freon
c) Iodoform
d) DDT
Answer: a
Clarification: Acute chloroform intoxication can cause depression of the central nervous system and may lead to death from lethal arrhythmias or respiratory arrest. Thus, the organic solvent is no longer in clinical use as an anaesthetic, but still plays a role in cases of suicide, homicide or inhalation for psychotropic effects.

8. How Benzene hexachloride (BHC) is used?
a) Insecticides
b) Fertilizers
c) Anaesthetics
d) Antiseptics
Answer: a
Clarification: Benzene hexachloride. Benzene hexachloride (BHC), any of several stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane formed by the light-induced addition of chlorine to benzene. One of these isomers is an insecticide called lindane, or Gammexane.

9. Depletion of Ozone is believed to increase which of the following?
a) Population
b) Ultraviolet rays
c) Pollution
d) Greenery
Answer: b
Clarification: Ozone layer depletion increases the amount of UVB that reaches the Earth’s surface. Laboratory and epidemiological studies demonstrate that UVB causes non-melanoma skin cancer and plays a major role in malignant melanoma development.

10. Which is the correct formula of Freon-12?
a) CCl₂F₂
b) CClF₃
c) CHCl₂F
d) CCl₃F
Answer: a
Clarification: As we can see below molecular diagram of Freon-12, the correct molecular formula is CCl₂F₂.

Organic Chemistry Multiple Choice Questions on “Preparations of Glycerol”.

1. Glycerol can be formed through digestion of which of the following?
a) galactose
b) fats
c) glucose
d) sucrose
Answer: b
Clarification: Heating fats(triglyceride) will leads to formation of glycerol along with formation of corresponding acid.

2. What is the name of the process of formation of glycerol via formation of allyl chloride?
a) Epichlorohydrine
b) Acrolein
c) Propylene oxide
d) Chloroform process
Answer: a
Clarification: The epichlorohydrin process is the most important; it involves the chlorination of propylene to give allyl chloride, which is oxidized with hypochlorite to dichlorohydrins, which reacts with a strong base to give epichlorohydrin. This epichlorohydrin is then hydrolyzed to give glycerol.

3. Fatty acids and glycerol (C₃H₈O₃) are produced after hydrolysis of which of the following?
a) amino acids
b) fats
c) starch
d) cellulose
Answer: b
Clarification: On hydrolysis in presence of an alkali, the tri esters yield glycerol and the fall of the carboxylic acids.

4. What is the middle product ‘A’ in the formation of the glycerol by propylene?

a) Allyl chloride
b) Vinyl chloride
c) Acyl chloride
d) Dichloroalkane
Answer: a
Clarification: The epichlorohydrin process is the most important; it involves the chlorination of propylene to give allyl chloride, which is oxidized with hypochlorite to dichlorohydrins, which reacts with a strong base to give epichlorohydrin. This epichlorohydrin is then hydrolyzed to give glycerol.

5. What is the product A formed by the partial oxidation using metal oxides and air of propylene or the given preparation of the glycerol?

a) Propene
b) Acroline
c) Propylene oxide
d) Propanol
Answer: b
Clarification: Processes from propylene include the synthesis of glycerol from acrolein by partial oxidation of propylene. Acrolein further form propen-3-ol and then hydrolyzed to give glycerol.

6. What is the product A formed by the partial oxidation using tert- butyl hydroperoxides or hydrogen peroxide of propylene or the given preparation of the glycerol?

a) Propene
b) Acroline
c) Propylene oxide
d) Propanol
Answer: c
Clarification: Processes from propylene include the synthesis of glycerol from propylene oxide is from oxidation by H₂O₂ or tert- butyl hydroperoxides of propylene. Propylene oxide further form propen-3-ol and then hydrolyzed to give glycerol.

7. Why synthetic production of glycerol is not commercially successful?
a) Because process is expensive
b) Because no marketing demands
c) Because process is hazardous
d) Because of the large-scale production of biodiesel from fats
Answer: c
Clarification: Because of the large-scale production of biodiesel from fats, where glycerol is a waste product, the market for glycerol is depressed. Thus, synthetic processes are not economical. Owing to oversupply, efforts are being made to convert glycerol to synthetic precursors, such as acrolein.

8. Which of the following is not the step for the isolation of glycerine form spent lye?
a) Brine Solution Preparation
b) Saponification and salting
c) Zone distillation
d) Glycerin Recovery from Spent Soap Lye
Answer: c
Clarification: Here zone distillation is not possible as constituents are in liquid phase. Glycerol is a high boiling liquid with boiling point 290℃. Here distillation will be done under high pressure at different temperature.

9. What will be the product X in the formation of glycerol?

a) R-ONa
b) RCOH
c) RCOONa
d) R-ONa and RCOONa both can be formed
Answer: c
Clarification: On hydrolysis in presence of an alkali, the tri esters yield glycerol and the fall of the carboxylic acids.