300+ REAL TIME Organic Chemistry Objective Questions & Answers 2023

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.

250+ TOP MCQs on Reactions of Glycols and Answers

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

1. Which catalyst is used for reaction of ethylene glycol with acetic acid?
a) Amberlyst 36
b) Hydrogen peroxide
c) Potassium permanganate
d) Aluminium bromide
Answer: a
Clarification: Esterification of ethylene glycol with acetic acid to ethylene glycol monoacetate and ethylene glycol diacetate using the acidic ion-exchange resin Amberlyst 36 as catalyst were investigated.

2. What is the principle product of the acid catalysed reaction of acetone and ethylene glycol?
a)
b)
c)
d)
Answer: b
Clarification: According to the given reaction between acetone and glycol, we can show that cyclic ketal is the product.

3. What will be the product when ethylene glycol and terephthalic acid reacts?
a)
b)
c)
d)
Answer: d
Clarification: Chemical Reaction between ethylene glycol and terephthalic acid yields BHET.

4. What happens when glycol reacts with lead tetraacetate?
a) No reaction
b) Ketones will be formed
c) Aldehyde will not be formed
d) Monohydric alcohols will be formed
Answer: b
Clarification: Lead tetraacetate is used cleave a carbon-carbon bond in a glycol. This reaction is useful in the formation of ketones and aldehydes and involves a favourable five membered cyclic intermediate.

5. What is the intermediate form in the mechanism of the lead acetate and glycol?
a) Three membered cyclic ring
b) Four membered cyclic ring
c) Five membered cyclic ring
d) Six membered cyclic ring
Answer: b
Clarification: Lead tetraacetate is used cleave a carbon-carbon bond in a glycol and involves a favourable five membered cyclic intermediate, as shown in given reaction.

6. What is the name of the reaction when lead tetraacetate is used cleave a carbon-carbon bond in a glycol?
a) Criegee oxidation
b) Swern oxidation
c) Baeyer-Villiger Oxidation
d) Jones oxidation
Answer: a
Clarification: The oxidation of 1,2‐diols (or glycols) to aldehydes or ketones with lead tetraacetate [Pb(OAc)4, LTA] via the cleavage of C‐C bond between the hydroxyl‐carrying carbon atoms is generally known as Criegee Glycol oxidation. This reaction has been reported to occur only in anhydrous organic solvent.

7. Which of the following statement is not true about criegee oxidation?
a) The oxidative cleavage of an alpha,beta-diol using lead tetraacetate to give the corresponding carbonyl compounds
b) It is analogous but milder than the Malaprade reaction
c) This oxidation was discovered by Rudolf Criegee and coworkers and first reported in 1931
d) Rate of reaction do not depend upon stereochemistry of glycol
Answer: d
Clarification: The rate of the reaction is highly dependent on the conformation of the diols, so much so that diols that are cis on certain rings can be reacted selectively as opposed to those that are trans on them.

8. Criegee oxidation of glycol should be performed in which type of medium?
a) Hydrous
b) Anhydrous
c) Acidic
d) Basic
Answer: b
Clarification: It was heavily stressed by Criegee that the reaction must be run in anhydrous solvents, as any water present would hydrolyze the lead tetraacetate; however, subsequent publications have shown that if the oxidation is faster than the rate of hydrolysis, the cleavage can be run in wet solvents or even aqueous solutions.

9. What happens when glycol reacts with periodic acid?
a) No reaction
b) Ketones will be formed
c) Aldehyde will not be formed
d) Monohydric alcohols will be formed
Answer: b
Clarification: Oxidation with Periodic Acid is used to cleave vicinal diols (a total of two alcohols, one on two adjacent carbons) into two carbonyl molecules.

10. Ethylene glycol on treatment with phosphorus tri-iodide yields
a) ethyl iodide
b) ethylene di-iodide
c) ethylene
d) ethane
Answer: b
Clarification: Phosphorus triiodide (PI₃) is an unstable red solid which reacts violently with water. It is a common misconception that PI₃ is too unstable to be stored; it is, in fact, commercially available. It is widely used in organic chemistry for converting alcohols to alkyl iodides.

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

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.

8. Which one is strongest acid among following options?
a) CH₂FCOOH
b) CH₂ClCOOH
c) CHCl₂COOH
d) CHF₂COOH
Answer: b
Clarification: CHF₂−COOH. Difluoroacetic acid is strongest because presence of two F atoms increases its acidic nature.

9. Acetic acid is weak acid than sulphuric acid because which of the following reasons?
a) It decomposes on increasing temperature
b) It has less degree of ionisation
c) It has -COOH group
d) It has more inductive effect
Answer: b
Clarification: CH₃COOH is slightly ionised than H₂SO₄. Acetic acid is weak acid than sulphuric acid because It has less degree of ionization.

10. In CH₃COOH and HCOOH, HCOOH will be which of the following?
a) Less acidic
b) Equally acidic
c) More acidic
d) cannot say about acidic behaviour
Answer: c
Clarification: Presence of methyl group decreases the acidic character of acetic acid due to positive inductive effect (+I).

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250+ TOP MCQs on Benzene Diazonium Chloride – 1 and Answers

Organic Chemistry Multiple Choice Questions on “Benzene Diazonium Chloride – 1”.

1. What is the general formula of Diazonium salt?
a) RN₂⁺X^–
b) RN⁺
c) RXI
d) RN₂⁺HSO^–₂
Answer: a
Clarification: Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group R−N₂⁺X^– where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halogen.

2. What is the known name of the given reaction?
C₆H₅N⁺₂ + CuCl → C₆H₅Cl + N₂ + Cu⁺
a) Gattermanns reaction
b) Sandmeyers reaction
c) Dehydrogenation reaction
d) Esterification reaction
Answer: b
Clarification: Benzene diazonium chloride heated with cuprous chloride or cuprous bromide respectively dissolved in HCl or HBr yield chlorobenzene or Bromobenzene, respectively.

3. What is the known name of the given reaction?
C₆H₅N⁺₂ + CuX → C₆H₅X + N₂ + Cu⁺
a) Gattermanns reaction
b) Sandmeyers reaction
c) Dehydrogenation reaction
d) Esterification reaction
Answer: a
Clarification: In the Gatterman reaction, benzene diazonium chloride is warmed with copper powder and HCl or HBr to produce chlorobenzene and bromobenzene respectively.

4. What is the known name of the given reaction?
[C₆H₅N⁺₂]Cl⁻ + C₆H₆ → C₆H₅−C₆H₅ + N₂ + HCl
a) Gattermanns reaction
b) Sandmeyers reaction
c) Gomberg–Bachmann reaction
d) Esterification reaction
Answer: c
Clarification: The aryl group can be coupled to another using aryldiazonium salts. For example, treatment of benzene diazonium chloride with benzene (an aromatic compound) in the presence of sodium hydroxide gives diphenyl. This reaction is known as the Gomberg–Bachmann reaction.

5. What is the known name of the given reaction?
[C₆H₅N⁺₂]BF⁻₄ → C₆H₅F + BF₃ + N₂
a) Gattermanns reaction
b) Sandmeyers reaction
c) Dehydrogenation reaction
d) Balz-Schiemann reaction
Answer: d
Clarification: Fluorobenzene is produced by thermal decomposition of benzene diazonium fluoroborate. The conversion is called the Balz-Schiemann reaction.

6. What is the known name of the given reaction?
[C₆H₅N⁺₂]Cl⁻ + ArCH=CHCO₂H → ArC=C−C₆H₅ + N₂ + CO₂ + HCl
a) Gattermanns reaction
b) Sandmeyers reaction
c) Meerwein reaction
d) Balz-Schiemann reaction
Answer: a
Clarification: Benzenediazonium chloride reacts with compounds containing activated double bonds to produces phenylated products. The reaction is called the Meerwein arylation.

7. Benzene diazonium chloride when reacts with hypophosphorus acid produces which of the following compound?
a) Benzene
b) Phenyl phosphate
c) Phenol
d) Phenyl isocyanide
Answer: a
Clarification: Arene diazonium cations are reduced by hypophosphorous acid or sodium stannite gives benzene:
[C₆H₅N⁺₂]Cl⁻ + H₃PO₂ + H₂O → C₆H₆ + N₂ + H₃PO₃ + HCl

8. p-amino azo benzene is obtained by treating diazonium chloride with which of the following compound?
a) Benzene
b) Aniline
c) Phenol
d) Benzoic acid
Answer: b
Clarification: p-amino azo benzene is obtained by treating diazonium chloride with aniline. The reactions are specifically acid catalyzed and involve pre‐equilibrium formation of amine and diazonium salt followed by rate‐limiting attack of the diazonium ion at a C‐atom (C‐coupling) to give the corresponding aminoazo compounds.

9. When hypophosphorous acid is treated with diazonium salts, it is reduced to which of the following compound?
a) Arene
b) Methane
c) Ethyl alcohol
d) Amines
Answer: a
Clarification: When hypophosphorous acid is treated with diazonium salts it is reduced to arene. Arene diazonium cations are reduced by hypophosphorous acid or sodium stannite gives benzene:
[C₆H₅N⁺₂]Cl⁻ + H₃PO₂ + H₂O → C₆H₆ + N₂ + H₃PO₃ + HCl.

10. Which of the following amine will form stable diazonium salt at 273-283 K?
a) C₆H₅NH₂
b) C₆H₅N(CH₃)₂
c) C₂H₅NH₂
d) C₆H₅CH₂NH₂
Answer: a
Clarification: Diazonium salts are prepared by treatment of aromatic amines i.e. aniline (C₆H₅NH₂) with nitrous acid and additional acid. Usually the nitrous acid is generated in situ (in the same flask) from sodium nitrite and the excess mineral acid.

250+ TOP MCQs on Nucleophilic Substitution in Pyridine and Answers

Organic Chemistry Multiple Choice Questions on “Nucleophilic Substitution in Pyridine”.

1. At which position of pyridine nucleophilic substitution reaction is most preferred?
a) First and third
b) Second
c) Third
d) Second and Forth
Answer: d
Clarification: When the nucleophile is at the 2 and 4 positions, the intermediate anion is stabilized by the electronegative nitrogen atom. This results in a more stable anion as compared to the intermediate anion when the nucleophile is at the 3 positions. Hence, the 2 and 4 positions is preferred for nucleophilic substitution.

2. Pyridine undergoes nucleophilic substitution with NaNH2 at 100℃ to give which of the following?
a) 3-aminopyridine
b) 2-aminopyridine
c) 3,5-diaminopyridine
d) 2,5-diaminopyridine
Answer: b
Clarification: Here, sodium amide is used as the nucleophile yielding 2-aminopyridine. The hydride ion released in this reaction combines with a proton of an available amino group, forming a hydrogen molecule.

3. Pyridine undergoes nucleophilic substitution with excess of NaNH₂ at 100℃ to give which of the following?
a) 3-aminopyridine
b) 2,6-diaminopyridine
c) 3,5-diaminopyridine
d) 2,5-diaminopyridine
Answer: b
Clarification: Sodium amide in excess is used as the nucleophile yielding 2,6-diaminopyridine. The hydride ion released in this reaction combines with a proton of an available amino group, forming a hydrogen molecule.

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

a) 3-aminopyridine
b) 2-aminopyridine
c) 3,5-diaminopyridine
d) 2,5-diaminopyridine
Answer: b
Clarification: We can see the ease of replacement of halogens in these positions by nucleophiles. The intermediate anion is stabilized by electronegative nitrogen and by delocalization round the ring.

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

a) 3-chloropyridine
b) 2-dichloropyridine
c) 3,5-dichloropyridine
d) 2,5-dichloropyridine
Answer: b
Clarification: This is the direct conversion to chloropyridines with POCl₃. The reaction starts by attack of the oxygen atom at phosphorus to create a leaving group, followed by aromatic nucleophilic substitution.

6. Nucleophilic 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) No specific condition requirements
Answer: d
Clarification: The nitrogen atom makes pyridines more reactive towards nucleophilic substitution, particularly at the 2- and 4-positions, by lowering the LUMO energy of the π system of pyridine.

7. What is the name of the following reaction?

a) Chichibabin reaction
b) Dealkylation of pyridine
c) Hantzsch pyridine synthesis
d) Bonnemann cyclisation
Answer: a
Clarification: The Chichibabin reaction is a method for producing 2-aminopyridinederivatives by the reaction of pyridine with sodium amide. The direct amination of pyridine with sodium amide takes place in liquid ammonia. Following the addition elimination mechanism first, a nucleophilic NH₂⁻ is added while a hydride (H⁻) is leaving.

8. Electron-withdrawing groups inhibit the Chichibabin reaction. Which of the following statement is not true about this fact?
a) they increase the basicity of the ring nitrogen
b) these electron-withdrawing groups can also form complexes with sodium amide
c) for single electron transfer pathway, altering the distribution of spin density of the intermediate radical anion
d) they slow down the sorption on sodium amide
Answer: a
Clarification: Electron-withdrawing groups inhibit the Chichibabin reaction they decrease the basicity of the ring nitrogen by decreasing the density of electron on nitrogen. So the donation of an electron is less.