Chem-8: Organic Chemistry - Some Basic Principles and Techniques30 Questions
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1. Organic chemistry is primarily concerned with the study of compounds containing:
A. Carbon
B. Nitrogen only
C. Oxygen only
D. Metals only
Answer: A. Carbon
Explanation: Organic chemistry is the branch of chemistry dedicated to studying carbon-containing compounds and their properties.
2. The unique ability of carbon atoms to form long chains by bonding with other carbon atoms is called:
A. Catenation
B. Isomerism
C. Hybridisation only
D. Polymerisation only
Answer: A. Catenation
Explanation: Catenation refers to carbon's remarkable ability to bond repeatedly with itself, forming extended chains or rings unique among elements.
3. Compounds containing only carbon and hydrogen atoms are called:
A. Hydrocarbons
B. Carbohydrates only
C. Alcohols
D. Amines
Answer: A. Hydrocarbons
Explanation: Hydrocarbons are the simplest class of organic compounds, composed exclusively of carbon and hydrogen atoms.
4. A group of atoms responsible for the characteristic chemical properties of an organic compound is called a:
A. Functional group
B. Substituent only
C. Isomer
D. Homologous series
Answer: A. Functional group
Explanation: The functional group is the specific atom or group of atoms within a molecule that determines its characteristic chemical reactivity.
5. A series of compounds with the same functional group, differing by a -CH₂- unit, is called a:
A. Homologous series
B. Isomeric series
C. Polymer chain
D. Catenated series
Answer: A. Homologous series
Explanation: A homologous series consists of compounds sharing the same general formula and functional group, each differing from the next by a CH₂ unit.
6. Compounds having the same molecular formula but different structural arrangements are called:
A. Isomers
B. Homologues
C. Polymers
D. Allotropes
Answer: A. Isomers
Explanation: Isomers share an identical molecular formula but differ in the arrangement of atoms, resulting in distinct structures and properties.
7. The type of isomerism arising from differences in the carbon skeleton of a molecule is called:
A. Chain isomerism
B. Positional isomerism
C. Functional isomerism
D. Geometrical isomerism
Answer: A. Chain isomerism
Explanation: Chain isomerism occurs when isomers differ in the arrangement or branching pattern of their carbon skeleton.
8. The type of isomerism arising from the different position of a functional group on the same carbon skeleton is called:
A. Positional isomerism
B. Chain isomerism
C. Functional isomerism
D. Optical isomerism
Answer: A. Positional isomerism
Explanation: Positional isomerism occurs when the functional group is attached at different positions along an otherwise identical carbon chain.
9. The process of separating a mixture of liquids with different boiling points is called:
A. Distillation
B. Filtration
C. Crystallisation
D. Sublimation
Answer: A. Distillation
Explanation: Distillation separates liquid components of a mixture based on differences in their boiling points.
10. The technique used to purify solid organic compounds by dissolving and then allowing them to reform crystals is called:
A. Crystallisation
B. Distillation
C. Chromatography only
D. Sublimation only
Answer: A. Crystallisation
Explanation: Crystallisation purifies solids by dissolving them in a suitable solvent and allowing pure crystals to form as the solution cools or evaporates.
11. The technique used to separate substances based on their differing solubility and adsorption on a stationary phase is called:
A. Chromatography
B. Distillation
C. Crystallisation
D. Filtration
Answer: A. Chromatography
Explanation: Chromatography separates mixture components based on their differing affinities for a stationary phase versus a mobile phase.
12. The process of purifying a solid that sublimes directly from solid to gas without passing through a liquid phase is called:
A. Sublimation
B. Distillation
C. Crystallisation
D. Chromatography
Answer: A. Sublimation
Explanation: Sublimation purification exploits substances that transition directly from solid to gas, leaving behind non-sublimable impurities.
13. The qualitative test used to detect the presence of nitrogen, sulphur and halogens in an organic compound is called the:
A. Lassaigne's test
B. Litmus test
C. Flame test only
D. Titration test
Answer: A. Lassaigne's test
Explanation: Lassaigne's test (sodium fusion test) is a standard qualitative method used to detect nitrogen, sulphur and halogens in organic compounds.
14. Kjeldahl's method is specifically used for the quantitative estimation of:
A. Nitrogen
B. Sulphur
C. Halogens
D. Phosphorus
Answer: A. Nitrogen
Explanation: Kjeldahl's method is a widely used quantitative technique specifically for estimating the nitrogen content in organic compounds.
15. A curved arrow used to represent the movement of an electron pair in a reaction mechanism is called a:
A. Curved (fishhook or full-headed) arrow
B. Straight vector arrow
C. Dashed arrow only
D. Double-headed reaction arrow only
Answer: A. Curved (fishhook or full-headed) arrow
Explanation: In organic reaction mechanisms, curved arrows specifically depict the movement of electron pairs from one atom or bond to another.
16. A reactive intermediate carrying a positive charge on a carbon atom is called a:
A. Carbocation
B. Carbanion
C. Free radical
D. Carbene
Answer: A. Carbocation
Explanation: A carbocation is a reactive organic species characterised by a positively charged carbon atom with only three bonds.
17. A reactive intermediate carrying a negative charge on a carbon atom is called a:
A. Carbanion
B. Carbocation
C. Free radical
D. Carbene
Answer: A. Carbanion
Explanation: A carbanion is a reactive species featuring a negatively charged carbon atom bearing a lone pair of electrons.
18. A reactive species with an unpaired electron on a carbon atom is called a:
A. Free radical
B. Carbocation
C. Carbanion
D. Nucleophile only
Answer: A. Free radical
Explanation: A free radical is a highly reactive species characterised by having an unpaired electron, often on a carbon atom.
19. A species that donates an electron pair to form a new covalent bond is called a:
A. Nucleophile
B. Electrophile
C. Free radical
D. Carbene
Answer: A. Nucleophile
Explanation: Nucleophiles are electron-rich species that donate an electron pair to form a new bond with an electron-deficient centre.
20. A species that accepts an electron pair to form a new covalent bond is called an:
A. Electrophile
B. Nucleophile
C. Free radical
D. Base only
Answer: A. Electrophile
Explanation: Electrophiles are electron-deficient species that seek out and accept an electron pair to form a new bond.
21. The inductive effect refers to the displacement of electrons along a chain of atoms due to the:
A. Presence of an electronegative or electropositive atom/group
B. Presence of light energy only
C. Application of heat only
D. Presence of a catalyst only
Answer: A. Presence of an electronegative or electropositive atom/group
Explanation: The inductive effect describes how electronegativity differences cause a permanent, gradual displacement of electron density along a bonded chain.
22. The delocalisation of electrons in conjugated systems, often represented using resonance structures, is called the:
A. Resonance (mesomeric) effect
B. Inductive effect only
C. Hyperconjugation only
D. Steric effect
Answer: A. Resonance (mesomeric) effect
Explanation: The resonance or mesomeric effect describes the delocalisation of pi electrons across conjugated systems, stabilising the molecule.
23. The interaction between a sigma C-H bond and an adjacent empty or partially filled p-orbital is called:
A. Hyperconjugation
B. Resonance
C. Inductive effect
D. Tautomerism
Answer: A. Hyperconjugation
Explanation: Hyperconjugation involves the delocalisation of electrons from a sigma bond into an adjacent empty or partially filled p-orbital, providing extra stability.
24. The phenomenon in which a compound exists in two readily interconvertible structural forms in equilibrium is called:
A. Tautomerism
B. Isomerism only
C. Resonance only
D. Polymerism
Answer: A. Tautomerism
Explanation: Tautomerism describes the dynamic equilibrium between two structural isomers that readily interconvert, such as keto and enol forms.
25. IUPAC nomenclature provides a systematic method for:
A. Naming organic compounds based on standardised international rules
B. Measuring melting points
C. Determining molecular mass only
D. Testing for functional groups
Answer: A. Naming organic compounds based on standardised international rules
Explanation: IUPAC nomenclature offers a consistent, internationally recognised system for naming organic compounds based on their structure.
26. In IUPAC nomenclature, the longest continuous carbon chain in a molecule is called the:
A. Parent chain
B. Substituent chain
C. Side chain only
D. Functional chain
Answer: A. Parent chain
Explanation: The parent chain refers to the longest continuous sequence of carbon atoms, forming the base name of the compound in IUPAC nomenclature.
27. The presence of a triple bond in a hydrocarbon is indicated in IUPAC nomenclature by the suffix:
A. -yne
B. -ane
C. -ene
D. -ol
Answer: A. -yne
Explanation: The suffix '-yne' specifically indicates the presence of one or more carbon-carbon triple bonds in the IUPAC name.
28. The presence of a double bond in a hydrocarbon is indicated in IUPAC nomenclature by the suffix:
A. -ene
B. -ane
C. -yne
D. -oic acid
Answer: A. -ene
Explanation: The suffix '-ene' is used to denote the presence of one or more carbon-carbon double bonds in the compound's name.
29. Saturated hydrocarbons, containing only single bonds, are indicated in IUPAC nomenclature by the suffix:
A. -ane
B. -ene
C. -yne
D. -ol
Answer: A. -ane
Explanation: The suffix '-ane' denotes saturated hydrocarbons that contain exclusively single bonds between carbon atoms.
30. Purification and characterisation techniques in organic chemistry are essential primarily to:
A. Obtain pure compounds and confirm their identity and structure
B. Increase the cost of the compound only
C. Change the compound's chemical formula
D. Make the compound radioactive
Answer: A. Obtain pure compounds and confirm their identity and structure
Explanation: These techniques are crucial for isolating organic compounds in pure form and confirming their molecular identity for accurate study and use.
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