Organic Chemistry – Some Basic Principles and Techniques MCQ Quiz - Objective Question with Answer for Organic Chemistry – Some Basic Principles and Techniques - Download Free PDF

CONCEPT:

Identification of Metal Cyanide Complexes

• When potassium ferrocyanide (K₄[Fe(CN)₆]) reacts with various metal salts, different colored precipitates are formed due to the formation of metal ferrocyanide complexes.
• Each metal salt reacts with potassium ferrocyanide to form characteristic precipitates, which can be used for identification purposes:
  • AgNO₃ + K₄[Fe(CN)₆] → Yellow precipitate (Formation of silver ferrocyanide)
  • Pb(NO₃)₂ + K₄[Fe(CN)₆] → White precipitate (Formation of lead(II) ferrocyanide)
  • CuSO₄ + K₄[Fe(CN)₆] (neutralized with NH₄OH) → Light blue precipitate (Formation of copper(II) ferrocyanide)
  • NiSO₄ + K₄[Fe(CN)₆] → Dark green precipitate (Formation of nickel(II) ferrocyanide)
  • CaCl₂ + K₄[Fe(CN)₆] (neutralized with NaOH) → White precipitate (Formation of calcium ferrocyanide)

EXPLANATION:

• Option A: AgNO₃ + K₄[Fe(CN)₆] → Yellow precipitate: This is correct, as silver ferrocyanide forms a yellow precipitate.
• Option B: Pb(NO₃)₂ + K₄[Fe(CN)₆] → White precipitate: This is correct, as lead(II) ferrocyanide forms a white precipitate.
  2Pb(NO₃)₂(aq) + K₄Fe(CN)₆](aq) → Pb₂[Fe(CN)₆ 
• Option C: CuSO₄ + K₄[Fe(CN)₆] (neutralized with NH₄OH) → Light blue precipitate: This is incorrect, as copper(II) ferrocyanide forms a light blue precipitate when neutralized with ammonium hydroxide.
  2CuSO₄(aq) + K₄[Fe(CN)₆](aq) → Cu₂[Fe(CN)₆
• Option D: NiSO₄ + K₄[Fe(CN)₆] → Dark green precipitate: This is correct, as nickel(II) ferrocyanide forms a dark green precipitate.
• Option E: CaCl₂ + K₄[Fe(CN)₆] (neutralized with NaOH) → White precipitate: This is incorrect, as calcium ferrocyanide forms a white precipitate when neutralized with NaOH.

Therefore, the correct answer is: A, B, and D only.

CONCEPT:

Aromaticity

• Aromatic compounds are those that satisfy the Hückel's rule, which states that a molecule is aromatic if it has (4n + 2) π-electrons in a conjugated planar ring system, where n is an integer (n = 0, 1, 2, etc.).
• In contrast, non-aromatic compounds do not exhibit this rule and may either lack conjugation or planarity in their structure, resulting in instability or lack of aromaticity.

EXPLANATION:

• 
  Cyclooctatraene (C₈H₈) is non-aromatic, as it has 8 π-electrons (n = 2) and a conjugated, non-planar structure unsatisfying Hückel's rule. Therefore, this is non-aromatic.
• 
•  Cyclopentadiene anion is aromatic because it has 6 π-electrons in a conjugated planar ring structure, satisfying Hückel's rule.
• 
  Since it maintains the same conjugated structure with a 6-membered ring, it is aromatic as well.
• 
  The compound shown is a five-membered ring with sulfur. This structure, known as thiophene, is aromatic due to its conjugated π-electrons in a planar ring system, satisfying Hückel's rule.
• In conclusion, all the structures shown are aromatic.

Hence, the correct answer is option 2 i.e A non-aromatic and B, C, and D is anti-aromatic

CONCEPT:

Electrophilic Aromatic Substitution (EAS) and Nucleophilic Attack on Azoles

• In nitration of methyl-substituted azoles (like methylpyrazole), the electrophilic aromatic substitution (EAS) occurs preferably at the electron-rich ring position.
• In pyrazole, nitrogen at position (I) has a hydrogen, and nitrogen (II) is more nucleophilic due to lack of hydrogen and lone pair availability.
• Upon nitration, the nitro group is introduced at the 4-position of the pyrazole ring due to resonance and stability considerations.
• In the second step, nucleophilic attack occurs on an epoxide ring by the nitrogen with greater nucleophilicity (N(II)).

EXPLANATION:

• Step 1: The starting material is 3-methylpyrazole. Upon nitration with HNO₃/H₂SO₄, electrophilic substitution occurs, giving 4-nitro-3-methylpyrazole as intermediate 'X'.
• Step 2: Reaction with ethylene oxide in basic medium (NaOH) proceeds through ring opening. Nucleophilic attack takes place by N(II) on the epoxide, forming a 2-hydroxyethyl derivative at that nitrogen.

• Only option D shows:
  • 'X' as 4-nitro-3-methylpyrazole
  • 'Y' as its corresponding 2-hydroxyethylated product via nucleophilic attack of N(II)

Therefore, the correct answer is option 4.

CONCEPT:

Isomerism in Deuterated Compounds

• Deuterium (D) is a stable isotope of hydrogen, and its presence in organic compounds can lead to the formation of isomers when placed in different positions on a molecule.
• In the case of a compound with two chiral centers, different substitution patterns of deuterium can create distinct stereoisomers. These isomers differ in the spatial arrangement of their substituents around the chiral centers.
• When deuterium is substituted at different positions, such as in the case of a bromo-deuterated butane, the resulting compound's stereochemistry can vary, leading to different isomeric forms.

EXPLANATION:

• The compound in the question is a deuterated bromo-butane with molecular formula C₄H₈DBr. The presence of two chiral carbon atoms suggests that the molecule can have stereoisomers.
• The correct answer corresponds to the structure where deuterium is placed at the 3-position of the butane chain. This allows the formation of two distinct chiral centers at the 2nd and 3rd carbon atoms, creating stereoisomeric forms.
• Option 3, 2-Bromo-3-deuterobutane, is the correct answer, as it results in the formation of two chiral centers and potential stereoisomers due to the unique substitution pattern of deuterium and bromine.

Therefore, the correct isomer is 2-Bromo-3-deuterobutane, which leads to two chiral centers and distinct stereoisomeric forms.

CONCEPT:

Types of Isomers

• Metamers: Metamers are isomers that differ in the alkyl group attached to the same functional group. The difference lies in the chain length or branching.
• Positional Isomers: Positional isomers have the same functional group but are attached at different positions on the carbon chain.
• Functional Isomers: Functional isomers have the same molecular formula but belong to different functional groups.
• Tautomers: Tautomers are isomers that readily interconvert by the migration of a hydrogen atom and a double bond.

EXPLANATION:

• A. Propanamine and N-Methylethanamine: These are functional isomers. Both have the same molecular formula (C₃H₉N), but one is a primary amine (Propanamine) and the other is a secondary amine (N-Methylethanamine). Type: Functional isomers.
  
• B. Hexan-2-one and Hexan-3-one: These are positional isomers because the carbonyl group is attached to different positions on the carbon chain (position 2 in Hexan-2-one and position 3 in Hexan-3-one). Type: Positional isomers.
• 
• C. Ethanamide and Hydroxyethanimine: These are tautomers. Ethanamide (acetamide) and hydroxyethanimine exist in equilibrium, where a hydrogen atom and a double bond shift between nitrogen and oxygen. Type: Tautomers.
  
• D. o-Nitrophenol and p-Nitrophenol: These are metamers. Both have the same molecular formula, but the nitro group is in different positions on the benzene ring (ortho and para). Type: Metamers.
  

Therefore, the correct answer is: Option 4: A - III, B - I, C - IV, D - II

The correct answer is Option 1. 

 Key Points

• Arenes are a class of organic compounds that contain one or more aromatic rings, and they are also known as aromatic hydrocarbons.
• The term "arene" is often used to refer specifically to aromatic hydrocarbons that contain only one aromatic ring, whereas the term "polycyclic aromatic hydrocarbons" (PAHs) is used for compounds that contain two or more aromatic rings.
• Some common examples of arenes include benzene, toluene, and naphthalene.
• Aromatic hydrocarbons are widely used in industry and have many important applications, but some are also known to be harmful to human health and the environment.

Additional Information

•  Alkynes are a class of organic compounds that contain at least one carbon-carbon triple bond.
  • They are also known as acetylenes, which is a reference to the simplest alkyne, ethyne (also called acetylene).
  • Alkynes are characterized by their high reactivity due to the presence of the triple bond, which can undergo a variety of reactions such as addition, oxidation, and reduction.
  • Some common applications of alkynes include their use as starting materials for the synthesis of other organic compounds, as well as in the production of plastics, synthetic fibers, and pharmaceuticals.
  • Alkynes are also used in welding and cutting torches, as the high temperature produced by burning acetylene gas in the presence of oxygen can be used to melt or cut metals.

• Unsaturated hydrocarbons are a class of organic compounds that contain one or more carbon-carbon double bonds or triple bonds, which are referred to as "unsaturated" because they have fewer hydrogen atoms than their corresponding saturated hydrocarbons.

  • The most common types of unsaturated hydrocarbons are alkenes and alkynes, which contain carbon-carbon double bonds and triple bonds, respectively.

  • These double and triple bonds give unsaturated hydrocarbons their characteristic chemical reactivity, as they can undergo addition reactions to form new compounds.

• Saturated hydrocarbons are a class of organic compounds that contain only single bonds between carbon atoms, and therefore, each carbon atom is bonded to the maximum number of hydrogen atoms possible.

  • Because they have no carbon-carbon double or triple bonds, saturated hydrocarbons are referred to as "saturated" with hydrogen. The most common type of saturated hydrocarbon is the alkane, also known as a paraffin.

  • Alkanes have a general formula of CnH2n+2, where n is the number of carbon atoms in the molecule. For example, methane (CH4) is the simplest alkane and has one carbon atom, while ethane (C2H6) has two carbon atoms.

The correct answer is Option 3.

Key Points

• Calcium Sulphate Dihydrate (CaSO4.2H2O) is commonly known as “Gypsum”.
• When Gypsum is heated, it gets converted into Calcium Sulphate Hemihydrate (CaSO4.1/2H2O) or “Plaster of Paris (POP)”.
• This is prepared by heating the gypsum which contains calcium sulfate dihydrate (CaSO4.2H2O) to a temperature of about 150 deg C.
• When added water to the plaster of Paris (PoP), it will re-form into gypsum.​

Additional Information Some common chemical compounds with their common names are:-

Explanation:

The IUPAC name for the following compound is 3, 5-dimethyl-4-propylhept-1-en-6-yne.

In the case of the double bond and triple bond, the position is the same and the position of substituents is also the same, then the double bond is considered as senior so, the numbering starts from a double bond.

The correct answer is Furan.

Key Points

• Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom.
• Chemical compounds containing such rings are also referred to as furans.
• The chemical formula of Furan is C4H4O.
• Furan is a colorless, flammable, highly volatile liquid with a boiling point close to room temperature.

Additional Information

•  Acetic Acid:
  • Acetic acid, also known as ethanoic acid, is an organic compound with the formula CH3COOH.
  • It belongs to the family of carboxylic acids and is composed of a methyl group attached to a carboxyl functional group.
  • In pure form, acetic acid is often referred to as glacial acetic acid.
  • It is a colorless liquid that is corrosive and boils at 117.9 °C and melts at 16.6 °C. It is completely miscible with water.
  • Notably, acetic acid is the most important of the carboxylic acids, with a wide range of uses and applicability.
  • One common occurrence of acetic acid is in vinegar, where it is the primary component apart from water and trace elements.
  • In vinegar, the concentration of acetic acid is at least 4% by volume.
• Ethane:
  • Ethane is a colorless and odorless gas that belongs to the family of hydrocarbons, more specifically, the alkane series.
  • The chemical formula for ethane is C2H6, signifying that it contains two carbon atoms and six hydrogen atoms.
  • Saturated hydrocarbons like ethane are structurally the simplest hydrocarbon that contains a single carbon-carbon bond.
  • It can be found in abundant quantities in natural gas, making it a vital component for fuel generation.
  • In the laboratory, ethane can be prepared using sodium propionate.
  • The resulting compound is not only an important gaseous fuel but also holds a significant place in the study of organic chemistry.
• Methane:
  • ​Methane (CH4) is the simplest member of the paraffin series of hydrocarbons and is one of the most potent greenhouse gases.
  • This colorless, odorless gas can act as a significant heat-trapper in the atmosphere, thus contributing to global warming and climate change effects.
  • It's significant to note that although Methane is less prevalent in the atmosphere compared to Carbon Dioxide (CO2), it is a far more potent greenhouse gas.
  • In terms of its contribution to climate warming, it is considered the second-largest contributor after carbon dioxide.
  • In terms of its use, methane is a primary component of natural gas, a common source of energy for heating and electricity.
  • It is also a raw material in industrial chemical processes.

Concept:

The thermal decomposition of potassium permanganate produces potassium manganate, manganese (IV) oxide, and oxygen. 

\(2{\rm{KMn}}{{\rm{O}}_4}{\rm{\;}}\left( {\rm{X}} \right)\mathop \to \limits^{513{\rm{\;K}}} {{\rm{K}}_2}{\rm{Mn}}{{\rm{O}}_4}{\rm{\;}}\left( {\rm{Y}} \right) + {\rm{Mn}}{{\rm{O}}_2} + {{\rm{O}}_2}{\rm{\;}}\left( {{\rm{gas}}} \right)\)

\({\rm{Mn}}{{\rm{O}}_2} + {\rm{NaCl}} + {{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {\rm{MnS}}{{\rm{O}}_4} + {\rm{C}}{{\rm{l}}_2}{\rm{\;}}\left( {\rm{Z}} \right) + {\rm{N}}{{\rm{a}}_2}{\rm{S}}{{\rm{O}}_4} + {{\rm{H}}_2}{\rm{O}}\)

The thermal decomposition of an ‘Mn’ compound (X) is KMnO₄ (potassium permanganate) at 513 K results in compound Y, K₂MnO₄ is (Potassium manganate) along with MnO₂ (manganese (IV) oxide) and gaseous product. Here the MnO₂ reacts with NaCl (sodium chloride) and concentrated H₂ SO₄ (sulfuric acid) to give a pungent gas Z is Cl₂ (chlorine).

X = KMnO₄

Y = K₂MnO₄

Concept:

Isomers:

• These are the compounds that have the same molecular formula but different structures or stereochemistries.
• There is a wide range of classification of organic molecules based on their structures.

​

• Metamerism: When isomers have the same molecular formula but differ in nature of alkyl groups attached to it.

• A class of compounds that have the same molecular formula but can have different functional groups exhibit functional isomerism.

• Positional isomers: Isomers having different positions of their functional groups.

(iii) C₃H₇Cl represents two position isomers

• Optical isomerism:

  • When two isomers rotate plane polarised light in different directions, then they are known as optical isomers.
  • The phenomenon is known as optical isomerism.

Explanation:

• The molecular formula of propyl alcohol is C₃H₈O.
• In the positional isomers, these things might differ:
  • The position of the substituent.
  • The position of the functional group.
  • Arrangement of carbon atoms in the chain.
• The structure of  n- propyl alcohol and isopropyl alcohol are:

• It is clearly seen that in n-propyl alcohol, the functional group -OH is in position 1 whereas in isopropyl alcohol it is in position two.

Hence, they are positional isomers.

The correct answer is its chemical properties.Key Points

• The functional group in an organic compound determines its chemical properties.
• The properties of a functional group include its reactivity, polarity, and ability to participate in specific chemical reactions.
• A functional group is a specific arrangement of atoms within a molecule that imparts characteristic chemical properties to the compound.
• Examples of functional groups include alcohols, aldehydes, ketones, carboxylic acids, and amines.

Additional Information

• The nature of the carbon chain refers to whether it is straight or branched, saturated or unsaturated, or contains other substituents such as halogens or functional groups.
• These factors affect physical properties such as melting point, boiling point, and solubility.
• The length of the carbon chain can also affect physical properties such as boiling point and solubility.
• Molecular mass is a measure of the total mass of the atoms in a molecule, which affect physical properties such as density and boiling point.

The correct answer is Catalytic agent.

Key Points

Kjeldahl’s method:

• This method is used for the estimation of nitrogen.
• The nitrogen-containing compound is treated with concentrated H₂SO₄  to get ammonium sulfate which liberates ammonia on treatment with NaOH, ammonia is absorbed in known volume of standard acid.
• In this method CuSO₄ acts as a catalytic agent.
• Kjeldahl method is not applicable to compounds containing nitrogen in nitro and azo groups and nitrogen present in the ring (e.g. pyridine) as nitrogen of these compounds does not change to ammonium sulphate under these conditions.

The correct answer is -ide.Key Points

• The suffix "-ide" is added to the stem of the name of the element to form the name of negative ions consisting of a single atom.
• For example, chlorine forms chloride ion (Cl-) and oxygen forms oxide ion (O2-).

Additional Information

• The suffix "-ous" is used for naming cations with lower charge, such as Cu+ (cuprous ion).
• The suffix "-ic" is used for cations with higher charge, such as Cu2+ (cupric ion).
• The suffix "-onium" is used for naming positively charged ions composed of two or more atoms, such as ammonium ion (NH4+).
• The suffix "-ate" is used for naming oxyanions with higher oxidation state, such as sulfate ion (SO42-), while the suffix "-ite" is used for oxyanions with lower oxidation state, such as sulfite ion (SO32-).

Concept:

From question, the diagram given is:

\(\frac{{360^\circ }}{3} = 120^\circ \)

H’’ + H + H’