300+ REAL TIME Organic Chemistry Objective Questions & Answers 2023

Organic Chemistry Questions and Answers for Freshers on “Rate of Reaction”.

1. The rate of the reaction is equal to the product of three factors listed below except ____________
a) Collision frequency
b) Energy factor
c) Orientation factor
d) pH factor
Answer: d
Clarification: The reaction rate is given by the product of collision frequency (deals with concentration, pressure, and arrangement), energy factor (deals with distribution of kinetic energy), and orientation factor (probability factor).

2. Temperature and pressure are the only factors which affect the reaction rate.
a) True
b) False
Answer: b
Clarification: The rate of reaction is affected by three factors temperature, pressure, and concentration. All the three varies directly with the rate of the reaction.

3. The frequency of molecular collision increases if ____________
a) The concentration of product increases
b) The concentration of product decreases
c) The concentration of reactant increases
d) The concentration of reactant decreases
Answer: c
Clarification: The frequency of molecular collision increases varies directly with the concentration of the reactant.

4. Identify the true statement regarding catalyst.
a) Always decreases the rate of the reaction
b) Always increases the activation energy of the reaction
c) Actually participates in the reaction
d) Changes the equilibrium concentration of the product
Answer: c
Clarification: A catalyst is a substance which when added, only alters the reaction rate temporarily and does not have a permanent effect on them and hence, only the option “Always increases the activation energy of the reaction” gives a correct info from the given choices.

5. From the choices given below, identify the activation energy of a reaction whose rate constant increases by 100 when the temperature changes from 300K to 360K.
a) 53
b) 69
c) 35
d) 42
Answer: b
Clarification: By substituting the appropriate values in the formula: (R.T1.T2)/(T1-T2)*ln(k1/k2)
we can find the value of activation energy(Ea).

6. Identify the unit of “k” in moles/L for the rate law: k[A][B]pow2.
a) L/mol/s
b) L(pow2)/mol/s
c) L(pow2)* s(pow2)/mol(pow2)
d) s
Answer: d
Clarification: Rate = k[A][B](pow2) and hence k=rate/{[A][B](pow2)}.

7. Which among the following catalyst increases the rate of the reaction?
a) Calcium carbonate
b) Calcium chloride
c) Calcium hydroxide
d) Calcium sulphate
Answer: a
Clarification: Calcium carbonate has large surface area and hence it increases the reaction rate.

8. Which is not a type of catalyst?
a) Positive catalyst
b) Negative catalyst
c) Autocatalyst
d) Homogeneous catalysis
Answer: d
Clarification: Homogeneous catalysis is a phenomenon in which the catalyst takes part in the reaction and it is not a type of catalyst.

9. What is the speed of a chemical reaction?
a) Is independent of the contact surface
b) Is constant no matter what the temperature is
c) Varies inversely with the absolute temperature
d) Is extremely rapid between the ions in aqueous solution
Answer: d
Clarification: The speed of a chemical reaction is extremely rapid between the ions in aqueous solution because there are no bonds that need to be broken.

10. The overall order for the reaction 2A+ B—> 2C with rate equation rate=k[A]^2[B] is?
a) 0
b) 1
c) 2
d) 3
Answer: d
Clarification: The order of A in this reaction is 2 and the overall reaction is a third order reaction.

Organic Chemistry for Freshers,

Organic Chemistry test on “Nucleophilic & Electrophilic Substitution Reaction”.

1. What is the correct statement for the given reactions?

a) B reacts faster than A
b) Both give the same product
c) A gives trans and B gives c is product
d) A gives cis and B gives trans product
Answer: b
Clarification:

In reaction A, groups attached to benzene are on opposite plane so SNGP mechanism will be followed and B will undergo S_N2. Due to SNGP (A) reacts faster than B and both give same product.

2. Which of the following statement is incorrect about nucleophiles?
a) Nucleophiles have an unshared electron pair and can make use of this to react with an electron deficient species
b) The nucleophilicity of an element (an electron donor) generally increases on going down a group in the periodic table
c) A nucleophile is electron-deficient species
d) All good nucleophiles are good bases when we deal across the period
Answer: c
Clarification: A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction, it is an electron rich species.

3. What is the correct order of nucleophilicity in the following options?
a) (CH₃)₃CO^– > CH₃^–
b) CH₃S^– > CH₃SH
c) CH₃CH₂CH₂O^– < (CH₃)₃CO^–
d) (CH₃CH₂)₃N > (CH₃CH₂)₃P
Answer: b
Clarification: Alkoxides are weaker Nu^– than carbanion because negative charge on oxygen is more stable than carbon. CH₃CH₂CH₂O^– is more nucleophilic, due to less steric hindrance. The negative charge is more nucleophilic than a stable compound.

4. Which of the following order is correct for the solvolysis in 50% aqueous ethanol at 44.6^oC?
a)
b)
c)
d)
Answer: b
Clarification: Solvolysis is a nucleophilic substitution (S_N1) or elimination, where the nucleophile is a solvent molecule. Solvolysis order CH₃X < 1^o halide < 2^o halide < allylic halide < 3^o halide.

5. Identify correct step representing S_N1 mechanism for the cleavage of ether with HI.

a) 1 and 3
b) 2 and 3
c) 1 and 4
d) 2 and 4
Answer: b
Clarification: As we can see in below reaction first step is a slow step in which carbocation is formed. And the second step is fast where nucleophile will attach carbocation.

Compound	Approx. Relative rate
CH₃CH₂Br	1.0
CH₃CH₂CH₂Br	0.28
(CH₃)₂CHCH₂Br	0.030
(CH₃)₃ CCH₂Br	0.00000042

Organic Chemistry Multiple Choice Questions on “Electrophiles”.

1. Which of the following statement is incorrect about electrophiles?
a) Electrophiles are positively charged or neutral species having vacant orbitals
b) The electrophiles are attacked by the most electron-populated part of one nucleophile
c) Chemical species that do not satisfy the octet rule such as carbenes and radicals are electrophiles
d) Electrophiles are Lewis base
Answer: d
Clarification: Because electrophiles accept electrons, they are Lewis acids not Lewis base, according to Acid-Base reaction theories.

2. In addition of halogen (Bromine) to an alkene, how can we isolate a bromonium in the reaction?
a) increasing concentration of bromide ion
b) decreasing concentration of bromide ion
c) alkene with cation stabilising groups
d) alkene with less electrophilic centre
Answer: c
Clarification: A bromo-carbenium ion intermediate may be predominant instead of vicinyl dibromide if the alkene has a cation-stabilizing substituent like phenyl group. There is an example of the isolation of the bromonium ion.

3. Which of the following is not an electrophile?
a) (CH₃)₄N⁺
b) Cl₂
c) HBr
d) Br₂
Answer: a
Clarification: The ammonium ion cannot react at the N with a nucleophile because the N already has an octet of electrons.

4. Which of the following is not an electrophile?
a) H₂O
b) Cl₂
c) HBr
d) Br₂
Answer: c
Clarification: Hydrogen bromide is a strong acid, it is able to donate a proton to a molecule or anion with a nucleophilic site.

5. In the given molecule where will electrophile will attack?

a) I
b) II
c) III
d) IV
Answer: a
Clarification: -CH₃O is a +M group, so it has lone pair to donate to upcoming electrophile.

6. In the given molecule where will electrophile will attack?

a) I
b) II
c) III
d) IV
Answer: a
Clarification: -OCOR is a +M group, it is more electron rich than rest of the groups, so it has lone pair to donate to upcoming electrophile.

7. Which of the following is most readily undergo electrophilic attack?

a) I
b) II
c) III
d) IV
Answer: a
Clarification: I is most reactive towards electrophilic attack, as -OH is +M group therefore, here benzene will have more e- density than rest of the others.

8. What is the correct order for the rate of reaction for the electrophilic attack of the given compounds?

a) I > II > III
b) II > I > III
c) I < II < III
d) III > I > II
Answer: b
Clarification: Electronegativity trend is N < O < F, so III is the least electron rich ring therefore least favourable for electrophilic attack. Similarly, II is the most electron rich ring therefore most favourable for electrophilic attack.

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

a) 3-Bromophenol
b) 4- Bromophenol
c) 3,5-Dibromophenol
d) 2,4,6-Tribromophenol
Answer: d
Clarification: The polar solvent (i.e. water) induces a stronger dipole in Br-Br. A stronger electrophile (Br+) is produced that undergoes electrophilic aromatic substitution with the benzene ring more readily. Consequently, you get tri-bromination with Br(aq.).

10. Which ring will readily undergo electrophilic attack?

a) I
b) II
c) III
d) Both I and III
Answer: b
Clarification: Due to the presence of -NH₂ group electron will be transferred to the C of -CONH₂ group and that’s why it will not withdraw electron from benzene ring. So, electron density of ring II is most in all three rings and that is why electrophile will attack at ring II.

Organic Chemistry Multiple Choice Questions on “Reactions of Ethers”.

1. An ether is more volatile than an alcohol having the same molecular formula. What is the reason for this difference?
a) dipolar character of ethers
b) alcohols having resonance structures
c) inter-molecular hydrogen bonding in ethers
d) inter-molecular hydrogen bonding in alcohols
Answer: d
Clarification: The ether are less volatile than alcohol of same molecular mass because in alcohols there is intermolecular H-bonding which makes it less volatile and High B.P. But in case of ether there is no intermolecular H-Bonding which makes it more volatile and less B.P.

2. Ethers may be used as solvents because they react only with which of the following reactants?
a) Acids
b) Bases
c) Oxidising agent
d) Reducing agents
Answer: a
Clarification: Ethers resist the attack of nucleophiles and bases. However, they are very good solvents in many organic reactions due to their ability to solvate cations by donating the electron pair from oxygen atom. Ethers are generally less reactive and react only with acids.

3. What are the products when ethyl isopropyl ether is cleaved with concentrated HI?
a) ethanol and 2-iodo-2-methylpropane
b) ethanol and 2-methylpropane
c) iodoethane and isopropyl alcohol
d) iodoethane and 2-methylpropane
Answer: c
Clarification: Ether + HX → Alkyl halide + Alcohol, Halide attacks at less hindered site to produce alkyl halide. So, Ethyl isopropyl ether + HI/Heat/Water → Isopropyl alcohol + Iodoethane.

4. What are the products when tert-butyl ethyl ether is cleaved with concentrated HI?
a) iodoethane and tert-butanol
b) iodoethane and 2-iodo-2-methylpropane
c) ethanol and 2-iodo-2-methylpropane
d) ethanol and tert-butanol
Answer: c
Clarification: Ether + HX → Alkyl halide + Alcohol, Halide attacks at less hindered site to produce alkyl halide. Clearly the SN2 is not in play here, as the tertiary carbons are much too hindered for a backside attack. However, tertiary carbocations are relatively stable – and “ionization” (i.e. loss of a leaving group) leaves us with an alcohol (R-OH) and a tertiary carbocation, which can then be attacked by iodide ion to give R-I. Again, if excess HI is present then that alcohol will be converted into an alcohol. We’ll have more about that to say in a few posts actually.

5. Which pair of products would result from the acid cleavage of phenyl propyl ether with excess concentrated HBr at an elevated temperature?
a) Phenol and 1-propanol
b) Bromobenzene and 1-propanol
c) Bromobenzene and 1-bromopropane
d) Phenol and 1-bromopropane
Answer: d
Clarification: Ether + HBr —–> Alkyl bromide + Alcohol. Halide attacks at less hindered site to produce alkyl halide.
Ethyl phenyl ether + HBr/Heat/Water —-> Phenol + Bromoethane.

6. Select the ether among following that yields methanol as one of the products on reaction with cold hydroiodic acid.
a) 1-Methoxybutane
b) 1-Methoxy-2-methylpropane
c) 2-Methoxy-2-methylpropane
d) Methoxybenzene
Answer: c
Clarification: When one group is methyl and the other alkyl group is a tertiary group, the halide formed is a tertiary group, the halide formed is a tertiary halide. It is because the attack by I- takes place at that carbon of alkyl group, which has a greater electron pushing inductive effect and a lower electron density.

7. The boiling point of ethyl alcohol is much higher than that of dimethyl ether though both have the same molecular weight. Why?
a) Ether is insoluble in water
b) Methyl groups are attached to oxygen in ether
c) Dipole moment of ethyl alcohol is less
d) Ethyl alcohol shows hydrogen bonding
Answer: d
Clarification: Alcohols have much higher boiling points than the comparable alkanes or the related ethers because molecules of alcohols can interact through hydrogen bonding while those of alkanes and ethers cannot. Thus, Ethanol has a higher boiling point (78℃) than dimethyl ether (−25℃) though they have the same molecular weight.

8. Which pair of products would result from the acid cleavage of tert-butyl propyl ether with excess concentrated HBr at an elevated temperature?
a) tert-butyl bromide and propyl alcohol
b) tert-butyl bromide and propyl bromide
c) tert-butyl alcohol and propyl bromide
d) 2-methyl-2-butene and propyl bromide
Answer: b
Clarification: Ether + HX → Alkyl halide + Alcohol, Halide attacks at less hindered site to produce alkyl halide. Clearly the SN2 is not in play here, as the tertiary carbons are much too hindered for a backside attack. However, tertiary carbocations are relatively stable – and “ionization” (i.e. loss of a leaving group) leaves us with an alcohol (R-OH) and a tertiary carbocation, which can then be attacked by iodide ion to give R-I. Again, if excess HI is present then that alcohol will be converted into an alcohol. We’ll have more about that to say in a few posts actually.

9. Which of the following is the name reaction of the given reaction?

a) Wollf’s rearrangement
b) Favorskii rearrangement
c) Pinacol rearrangement
d) Claisen rearrangement
Answer: d
Clarification: The Claisen rearrangement is an organic reaction where an allyl vinyl ether is converted into an unsaturated carbonyl compound with the input of heat at 200-250^oC or a Lewis acid. This reaction belongs to a class of reactions termed “sigmatropic rearrangements” and it is a concerted process where bonds are forming and breaking at the same time.

10. Which of the following will be obtained by keeping ether in contact with air for a long time?
a) C₂H₅−O−CH (CH₃)−O−OH
b) C₂H₅−OCH₂−OH
c) C₂H₅−O−C₂H₅OH
d) CH₃−O CH (CH₃)−O−OH
Answer: a
Clarification: When stored in the presence of air or oxygen, ethers tend to form explosive peroxides, such as diethyl ether peroxide. The reaction is accelerated by light, metal catalysts, and aldehydes.
R−O−R’ + O₂/light → C₂H₅−O−CH(CH₃)−O−OH.

Organic Chemistry Multiple Choice Questions on “Condensation Reactions”.

1. Condensation reaction is the reverse of which of the following reaction?
a) lock and key hypothesis
b) oxidation
c) hydrolysis
d) glycogen formation
Answer: c
Clarification: This reaction example is the reverse of hydrolysis, which splits a chemical entity into two parts through action from the polar water molecule, which itself splits into hydroxide and hydrogen ions.

2. Condensation reaction always results in the formation of complex sugar (disaccharide or polysaccharide) and which of the following?
a) amino acids
b) lipids
c) water
d) maltose
Answer: c
Clarification: Condensation reaction always results in the formation of complex sugar (disaccharide or polysaccharide) and water.

3. In which condensation an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), followed by dehydration to give a conjugated enone happens?
a) Aldol condensation
b) Claisen reduction
c) Henry condensation
d) Knoevenagel condensation
Answer: a
Clarification: Aldol condensation in which condensation an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), followed by dehydration to give a conjugated enone happens.

4. Which combination of carbonyl compounds gives phenyl vinyl ketone by an aldol condensation?

a) Acetophenone and ketone
b) Acetophenone and aldehyde
c) Benzaldehyde and aldehyde
d) Benzaldehyde and ketone
Answer: a
Clarification: Draw the structures of the possible aldol products (3-hydroxy carbonyl compounds) before dehydration from the pairs of reactants shown below, then identify which aldol will lead to phenyl vinyl ketone upon dehydration.

5. Which ester will not give a good yield of the Claisen condensation product with NaOEt in EtOH?
a)
b)
c)
d)
Answer: c
Clarification: The Claisen condensation is reversible and it is formation of a stabilized enolate of the product which leads to a high yield at equilibrium. When the product cannot give a stabilized enolate, the yield will be poor.

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

a) trans-2,4-pentadienoic acid
b) cis -2,4-pentadienoic acid
c) 3-aminobenzoic acid
d) 2-aminobenzoic acid
Answer: a
Clarification: With malonic compounds the reaction product can lose a molecule of carbon dioxide in a subsequent step. In the so-called Doebner modification the base is pyridine. For example, the reaction product of acrolein and malonic acid in pyridine is trans-2,4-Pentadienoic acid with one carboxylic acid group and not two.

7. What will be the product of the following reaction?

a) –Nitro alcohol
b) -nitro alcohol
c) Nitroalkene
d) -amino alcohol
Answer: a
Clarification: This is a Henry Reaction, it is the combination of a nitroalkane and an aldehyde or ketone in the presence of a base to form β-Nitro alcohols.

8. What will be the product ‘B’ in the reaction?

a) α-nitro alcohol
b) α-nitro ketone
c) nitroalkene
d) β-amino alcohol
Answer: b
Clarification: This is a Henry Reaction, it is the combination of a nitroalkane and an aldehyde or ketone in the presence of a base to form β-Nitro alcohols, followed by oxidation of the secondary alcohol to yield α-nitro ketones.

9. What will be the product ‘B’ in the reaction?

a) α-nitro alcohol
b) α-nitro ketone
c) nitroalkene
d) β-amino alcohol
Answer: c
Clarification: This is a Henry Reaction, it is the combination of a nitroalkane and an aldehyde or ketone in the presence of a base to form β-Nitro alcohols, followed by dehydration of nitroalkene.

10. What will be the product ‘B’ in the reaction?

a) α-nitro alcohol
b) α-nitro ketone
c) nitroalkene
d) β-amino alcohol
Answer: d
Clarification: This is a Henry Reaction, it is the combination of a nitroalkane and an aldehyde or ketone in the presence of a base to form β-Nitro alcohols, followed by reduction of the nitro group to yield β-amino alcohols.

Organic Chemistry online test on “Preparation of Amines – 2”.

1. Which of the following reaction does not form amines?
a) RX + NH₃ →
b)

c) RCN + H₂O (^{underrightarrow{H^+}})
d) RCONH₂ + 4H (^{underrightarrow{LiAlH_4}})
Answer: c
Clarification: Nitrile gives carboxylic acid on hydrolysis and amines on reduction.

2. Starting from propanoic acid, the following reactions were carried out, what is the compound Z?

a) CH₃−CH₂−Br
b) CH₃−CH₂−NH₂
c) CH₃-CH₂-COBr
d) CH₃−CH₂−CH₂−NH₂
Answer: b
Clarification: Starting from propanoic acid, the following reactions were carried out, the compound is ethylamine.