300+ REAL TIME Organic Chemistry Objective Questions & Answers 2023

250+ TOP MCQs on Saponification and Answers

Organic Chemistry Multiple Choice Questions on “Saponification”.

1. Which of the following processes can saponification be used for?
a) For the production of plastics
b) In blow glass artistry
c) To make soap
d) The formation of alloys
Answer: c
Clarification: Saponification is a process that produces soap. Soaps are salts of fatty acids.

2. What is the name of the soap produced through the saponification of this triglyceride?

a) Sodium dececanoate
b) Sodium oleate
c) Sodium stearate
d) Sodium acetate
Answer: c
Clarification: The soap has the formula C₁₇H₃₅COONa and its name is sodium stearate.

3. Lye is used in soap-making. Lye is a concentrated solution of which ionic compound?
a) K₂CO₃
b) CuSO₄
c) NaOH
d) NaCl
Answer: a
Clarification: Lye is another name for a strongly basic solution. Mostly it is a solution of sodium hydroxide.

4. Which of the following term describe saponification?
a) Cleaving of ester molecules into carboxylic acid and alcohol
b) Dehydration synthesis by removing water
c) Hydrolysis of a salt by adding a weak acid
d) Synthesis of two alkyl groups to make an ether
Answer: a
Clarification: Cleaving of ester molecules into carboxylic acid and alcohol that is triglyceride is treated with a strong base, which cleaves the ester bond, releasing fatty acid salts (soaps) and glycerol.

5. Which of the following is considered a useful alkali in saponification reactions?
a) CCl₄
b) Cl^–
c) NaOH
d) Pb⁺
Answer: c
Clarification: Depending on the nature of the alkali used in their production, soaps have distinct properties. Sodium hydroxide (NaOH) gives “hard soap”; hard soaps can also be used in water containing Mg, Cl, and Ca salts.

6. Which of the following statement is true about saponification value of oil?
a) The shorter the chain of fatty acid, the higher is the saponification value
b) The shorter the chain of fatty acid, the higher is the saponification value
c) The higher the saturation in chain of fatty acid, the lower is the saponification value
d) The lower the saturation in chain of fatty acid, the higher is the saponification value
Answer: a
Clarification: The shorter the chain of fatty acid, the higher is the saponification value, the long chain fatty acids found in fats have a low saponification value because they have a relatively fewer number of carboxylic functional groups per unit mass of the fat as compared to short chain fatty acids.

7. Which of the following fat or oil is unsaponifiable?
a) Paraffin wax
b) Bee wax
c) Olive oil
d) Shea butter
Answer: a
Clarification: Unsaponifiables are components of an oily (oil, fat, wax) mixture that fail to form soaps when treated with sodium hydroxide (lye) or potassium hydroxide. Unsaponifiable value of paraffin wax is approximately 100.

8. Saponification value is the number of milligrams of KOH required to saponify what present in the 1g of oil or fat?
a) Salts
b) Hydrocarbon
c) Fatty acids
d) unsaturation
Answer: c
Clarification: The saponification is the value of oil determined as the number of mgs of KOH needed to saponify the fatty acids present in the 1g of oil.

9. Which of the following compound is an industrial manufacturing product by saponification?
a) Sodium chloride
b) Potassium hydroxide
c) Glycerol
d) Sodium hydroxide
Answer: c
Clarification: The triglyceride is treated with a strong base which cleaves the ester bond, releasing fatty acid salts (soaps) and glycerol. This process is also the main industrial method for producing glycerol. In some soap-making, the glycerol is left in the soap.

10. Soap can be precipitated out by salting by using which chemical compound?
a) Sodium chloride
b) Potassium hydroxide
c) Glycerol
d) Sodium hydroxide
Answer: a
Clarification: If necessary, soaps may be precipitated by salting it out with sodium chloride.

250+ TOP MCQs on Enantiomerism and Answers

Organic Chemistry Multiple Choice Questions on “Enantiomerism”.

1. Which of the following is the definition for enatiomerism?
a) A pair of stereoisomers each of which has two chirality centres
b) A pair of stereoisomers that are not mirror images of one another
c) A pair of stereoisomers that are non-superimposable mirror images of one another
d) Any pair of stereoisomers
Answer: c
Clarification: The relationship between two stereoisomers having molecules that are mirror images of each other; enantiomers have identical chemical and physical properties in an achiral environment but form different products when reacted with other chiral molecules and exhibit optical activity. A pair of stereoisomers that are non-superimposable mirror images of one another are enantiomers.

2. Which of the following statements is not true regarding pairs of enantiomers?
a) They have identical boiling points
b) They rotate plane polarized light in opposite directions
c) They react at identical rates with chiral reagents
d) They have identical melting points
Answer: b
Clarification: This statement is true. All (+) enantiomers are levorotatory, corresponding to rotation of plane polarized light in a clockwise direction.

3. Which of the following statements regarding optical rotation is not true?
a) All R enantiomers are dextrorotatory
b) All (+) enantiomers are laevorotatory
c) All (-) enantiomers rotate plane polarized light in a counter clockwise direction
d) (+) and (-) enantiomers rotate plane polarized light in opposite directions
Answer: c
Clarification: This statement is false. Pairs of enantiomers react at different rates with chiral reagents.

4. How many enantiomers are there of the molecule shown below?

a) 6
b) 2
c) 0
d) 1
Answer: c
Clarification: Chiral centers are carbons that have four non-identical substituents on them and are designated as either of R stereochemistry or S stereochemistry. If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa. And above compound does not satisfy these conditions to show enantiomerism.

5. Which of the following notations is not used to distinguish between pairs of enantiomers?
a) R and S
b) E and Z
c) + and –
d) D and L
Answer: b
Clarification: All four of these notations are used to distinguish between isomers, but only three are used specifically in the context of enantiomers. The fourth – E and Z – is used to differentiate between geometric isomers, not enantiomers.

6. Which among the following is true about enantiomerism?
a) Assignments of R and S labels and (+) and (–) labels are not connected
b) The labels R and S refer to different conformers
c) The labels (+) and (–) are used to distinguish enantiomers
d) The specific rotation of enantiomers is equal and opposite
Answer: b
Clarification: R and S not refers to different conformers. Chiral centers are carbons that have four non-identical substituents on them and are designated as either of R stereochemistry or S stereochemistry. If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa.

7. Which of the following molecules does not possess enantiomers?
a) CH₃CH₂CH₂CHBrCH₃
b) CH₃CH₂CBr₂CH₃
c) CH₃CHBrCH₂CH₃
d) CHBr₂CH₂CHBrCH₃
Answer: b
Clarification: For being an enantiomer it is necessary that carbon atom has four non-identical substituents around it, making this carbon a chiral center, and as proof of its chirality the molecule has a non-superimposable mirror image. Molecules that are mirror images of each other is enantiomers.

8. Which of the following is true of any (S)-enantiomerism?
a) It rotates plane-polarized light to the right
b) It rotates plane-polarized light to the left
c) It is a racemic form
d) It is the mirror image of the corresponding (R)-enantiomer
Answer: d
Clarification: Stereocenters, (sometimes called chiral centers) are carbons that have four non-identical substituents on them and are designated as either of R stereochemistry or S stereochemistry. If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa.

9. Which of the following is not true of enantiomers?
a) boiling point
b) melting point
c) specific rotation
d) density
Answer: c
Clarification: Enantiomers have identical chemical and physical properties in an achiral environment but form different products when reacted with other chiral molecules and exhibit optical activity. A pair of stereoisomers that are non-superimposable mirror images of one another are enantiomers.

10. In the absence of specific data, it can only be said that (R)–2–bromopentane is which of the following?
a) dextrorotatory (+)
b) levorotatory (–)
c) optically inactive
d) analogous in absolute configuration to (R)–2–chloropentane
Answer: d
Clarification: In the absence of specific data, it can only be said that (R)–2–bromopentane analogous in absolute configuration to (R)–2–chloropentane.

250+ TOP MCQs on Step Reaction Polymerisation and Answers

Organic Chemistry Multiple Choice Questions on “Step Reaction Polymerisation”.

1. Which of the following is true about Step-growth polymerisation?
a) radical, coordination, anionic, or cationic polymerization, depending on the type of initiation
b) polymerization that is catalysed by transition metal salts and complexes
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) monomers react to form first dimers, then trimmers, longer oligomers and eventually long chain polymers
Answer: d
Clarification: Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimmers, longer oligomers and eventually long chain polymer.

2. Which of the following is not true about step growth polymerisation?
a) Molar mass of backbone chain increases rapidly at early stage and remains approximately the same throughout the polymerization
b) Similar steps repeated throughout reaction process
c) Initiator are required for the step growth polymerisation
d) Rapid loss of monomer early in the reaction
Answer: c
Clarification: Initiator is not required for the step growth polymerisation. Step-Growth polymerization occurs by consecutive reactions in which the degree of polymerization and average molecular weight of the polymer increase as the reaction proceeds.

3. Which of the following is polymer formed by step-growth polymerization is not classified under condensation polymerisation?
a) Polyester
b) Polyurethane
c) Polysiloxane
d) Polyamide
Answer: b
Clarification: Most step-growth polymers are classified as condensation polymers, but not all step-growth polymers. Polyurethanes formed from isocyanate and alcohol bifunctional monomers) release condensates; in this case, we talk about addition polymers.

4. Which monomers are required for the formation of Bakelite via a typical step-growth polymerization?
a) phenol and formaldehyde
b) isocyanate and alcohol
c) diamine and formaldehyde
d) ester and phenol
Answer: a
Clarification: The synthesis of first truly synthetic polymeric material, Bakelite, was announced by Leo Baekeland in 1907, through a typical step-growth polymerization fashion of phenol and formaldehyde.

5. Formation of polytriazole polymers via step-growth polymerization is produced from which of the following monomers?
a) Compound which bears both alkyne and azide functional group
b) Compound which bears both alkene and azide functional group
c) Compound which bears both alkane and azide functional group
d) Compound which bears both vinyl and azide functional group
Answer: a
Clarification: Poly-Triazole polymers are produced from monomers which bear both an alkyne and azide functional group. The monomer units are linked to each other by the a 1,2,3-triazole group; which is produced by the 1,3-Dipolar cycloaddition, also called the Azide-alkyne Huisgen cycloaddition.

6. How does the reaction rate vary with increasing extent of reaction beyond 94% conversion in self catalyzed reaction?
a) decreases
b) increases
c) remains same
d) first increases than decreases
Answer: a
Clarification: The kinetics of the step-growth polymerization can be described with Flory’s equal reactivity principle. If the polymerization is carried out in the presence of a strong acid (sulfonic acids) and if the catalyst concentration is kept constant throughout the process the average degree of polymerization increases linearly with the reaction time, which is a much more favorable situation for obtaining high average molecular weight polymers than the weak-acid catalyzed third-order reaction.

7. What is the trend in the molecular weight of step growth polymer at lower conversion and higher conversion respectively?
a) Increase then decrease
b) Decreases an increases
c) Remains same
d) Can’t say about molecular weight
Answer: b
Clarification: Step-growth polymers increase in molecular weight at a very slow rate at lower conversions and reach moderately high molecular weights only at very high conversion (i.e., >95%).

8. Which of the following is not prepared by Ziegler-Natta coordination polymerisation?
a) High density Polyethylene (HDPE)
b) Ultrahigh molecular weight Polyethylene (UHMWPE)
c) Ethylene-1-alkenebcopolymer (linear low density polyethylene, LLDPE)
d) Polyvinyl acetate (PVAc)
Answer: d
Clarification: Vinyl chloride is polar olefins and such alkenes do not polymerize in the presence of Ziegler-Natta or Kaminsky catalysts.

250+ TOP MCQs on Isomerism and Answers

Organic Chemistry Multiple Choice Questions on “Isomerism”.

1. Choose the incorrect option regarding Isomerism.
a) They differ in both physical and chemical properties
b) They have the different molecular formula
c) There are two types of Isomerism : Structural and Stereo Isomerism
d) Geometric and optical isomerism are two types of Stereo Isomerism
Answer: b
Clarification: Isomers are compounds that have same molecular formula.

2. Isomerism that arises out of the difference in spatial arrangement of atoms or groups about the doubly bonded carbon atoms are called? (In specific)
a) Structural Isomerism
b) Stereo Isomerism
c) Geometrical Isomerism
d) Optical Isomerism
Answer: c
Clarification: These geometrical isomers are not mirror images of each other and they differ in spatial arrangement from one another.

3. Isomers with similar groups on the same side are called as ” trans” isomers.
a) True
b) False
Answer: b
Clarification: “Trans” isomers are those with similar groups arranged in opposite direction. The Isomers with similar groups on the same side are called as “cis” isomers.

4. Which among the following defines Meso forms of isomers?
a) Meso form is optically inactive due to external compensation
b) The molecules of the meso isomers are chiral
c) It can be separated into optically active enantiometric pairs
d) It is a single compound
Answer: d
Clarification: Meso forms of isomers are single compound and their molecules are achiral and hence they cannot be separated into pairs.

5. Which among the following does not exhibit geometric isomerism?
a) 1-hexene
b) 2-hexene
c) 3-hexene
d) 4-hexene
Answer: a
Clarification: Alkenes like 1-hexene when flipped from top to bottom they have identical structures and also they have C=CH₂ unit which does not exist as cis-trans isomers.

6. Which among the following is formed when an alcohol is dehydrated?
a) alkane
b) alkyne
c) alkene
d) aldehyde
Answer: c
Clarification: In elimination reaction, when protic acids react with alcohol, they lose water molecule to form alkenes.

7. A fat on hydrolysis would yield?
a) Glycerol and soap
b) Ethanol and soap
c) Ethanol and glycerol
d) Only soap
Answer: a
Clarification: During saponification process, fat on hydrolysis will yield glycerol and soap.

8. Which among the following correctly defines Diastereomer?
a) These have same magnitude but different signs of optical rotation
b) Nonsuperimposable object mirror relationship
c) These differ in all physical properties
d) Separation is very difficult
Answer: c
Clarification: Diastereomers differ in all physical properties. The rest of the points are related to Enantiomers.

9. The molecular formula C₅H₁₂ contains how many isomeric alkanes?
a) 1
b) 2
c) 3
d) 4
Answer: c
Clarification: n-pentane, 2-ethylpropane, and 2-methylbutane are the 3 isomeric alkanes of C₅H₁₂ (pentane).

10. Identify the chiral molecule among the following.
a) Isopropyl alcohol
b) 2-pentanol
c) 1-bromo 3-butene
d) Isobutyl alcohol
Answer: d
Clarification: Chirality is the condition for a molecule to be optically active and here isobutyl alcohol is the only compound is optically active and hence it is the chiral molecule.

250+ TOP MCQs on Rearrangement Reactions and Answers

Organic Chemistry Multiple Choice Questions on “Rearrangement Reactions”.

1. Which types of isomers are formed in rearrangement reactions?
a) structural isomers
b) Geometrical isomers
c) Optical isomer
d) Conformational isomers
Answers: a
Clarification: Products formed have the same molecular formula, but their atoms have different arrangements or bonds. For example, Butane and isobutane have the same number of carbon (C) atoms and hydrogen (H) atoms, so their molecular formulas are the same.

2. What is the main difference between Hofmann and Curtius rearrangement?
a) Products are different
b) Intermediate formed is different
c) Reactants are different
d) Isomers
Answers: c
Clarification: The Hofmann rearrangement occurs with an amide. The Curtius rearrangement occurs with an acyl azide.

3. With accompanying 1, 2-rearrangement in wolff rearrangement, an α-diazocarbonyl compound is converted into a ketene by loss of which of the following compound?
a) Dioxygen
b) Dinitrogen
c) Disulphur
d) Ammonia
Answer: b
Clarification: The leaving group (N₂) and the migrating group (R₁) are antiperiplanar, which favors a concerted mechanism, in which nitrogen extrusion occurs concurrently with 1, 2-alkyl shift.

4. Which Intermediate is formed in Wolff’s reaction?
a) Carbene
b) Ketene
c) Carbocation
d) Carbanion
Answers: b
Clarification: Ketene is formed as intermediate in Wolff’s reaction. Formation of Diazonium ion will be followed by reaction in presence of heat which leads to rearrangement of bonds and ketene will be formed.

5. Which was the first molecular rearrangement identified as such by early chemists?
a) Wolff’s rearrangement
b) Pinacole rearrangement
c) Favorskii rearrangement
d) Hofmann rearrangement
Answers: b
Clarification: The pinacol rearrangement was the first molecular rearrangement identified as such by early chemists.

6. Which intermediate carbocation is more stable in pinacole -pinacolone rearrangement?
a) 1^o
b) 2^o
c) 3^o
d) 4^o
Answer: c
Clarification: 3^o-carbocation is relatively stable, and has been shown to return to pinacol by reaction in the presence of isotopically labeled water. A 1, 2-methyl shift generates an even more stable carbocation in which the charge is delocalized by heteroatom resonance.

7. In which medium Favorskii rearrangement occurs?
a) Acidic
b) Basic
c) Neutral
d) Alkaline
Answer: b
Clarification: It is a base catalysed reaction:

Mechanism of Favorskii rearrangement: Here OH- group of NaOH is attaching at the keto-group and the ring will open for the stability of the molecule.

8. The benzylic acid rearrangement reaction of a cyclic diketone leads to _______
a) Ring expansion
b) Ring contraction
c) Ring fusion
d) Isomers
Answer: b
Clarification: The benzylic acid rearrangement reaction of a cyclic diketone leads to ring contraction as shown in below diagram.