Ch-8: Organic Chemistry – Some Basic Principles and Techniques30 Questions
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1. Homolytic cleavage of a covalent bond produces:
A. Free radicals
B. Carbocations
C. Carbanions
D. Electrophiles
Answer: A. Free radicals
Explanation: Homolytic fission involves equal sharing of bonding electrons, yielding neutral species with single unpaired electrons (free radicals).
2. Heterolytic cleavage of a covalent bond results in the formation of:
A. Cations and Anions
B. Free radicals
C. Neutral molecules
D. Uncharged species
Answer: A. Cations and Anions
Explanation: Heterolytic cleavage leaves both bonding electrons with the more electronegative atom, producing positive and negative ions.
3. What is the hybridization state of carbon in methane (CH₄)?
A. sp³
B. sp²
C. sp
D. dsp²
Answer: A. sp³
Explanation: The carbon atom in methane forms 4 single sigma bonds with tetrahedral geometry, requiring sp³ hybridization.
4. The shape of a carbocation (carbonium ion) is:
A. Trigonal planar
B. Pyramidal
C. Tetrahedral
D. Linear
Answer: A. Trigonal planar
Explanation: Carbon in a carbocation is sp² hybridized with six valence electrons, creating a flat trigonal planar geometry.
5. Which of the following carbocations is the most stable?
A. (CH₃)₃C⁺ (Tertiary)
B. (CH₃)₂CH⁺ (Secondary)
C. CH₃CH₂⁺ (Primary)
D. CH₃⁺ (Methyl)
Answer: A. (CH₃)₃C⁺ (Tertiary)
Explanation: Tertiary carbocations are stabilized by maximum hyperconjugation structures and +I inductive effects of three alkyl groups.
6. An electrophile is a reagent that:
A. Accepts an electron pair
B. Donates an electron pair
C. Donates a proton
D. Contains a negative charge only
Answer: A. Accepts an electron pair
Explanation: Electrophiles are electron-deficient species (Lewis acids) that seek out electron-dense sites.
7. Which of the following species acts as a nucleophile?
A. NH₃
B. BF₃
C. AlCl₃
D. NO₂⁺
Answer: A. NH₃
Explanation: Ammonia (NH₃) possesses an unshared lone pair of electrons on nitrogen, enabling it to act as a nucleophile.
8. What is the IUPAC name of CH₃-CH(OH)-CH₃?
A. Propan-2-ol
B. Propan-1-ol
C. Isopropyl alcohol
D. Propanone
Answer: A. Propan-2-ol
Explanation: The main chain contains 3 carbons with a hydroxyl group at position 2, giving Propan-2-ol.
9. Isomers having the same molecular formula but different functional groups are called:
A. Functional group isomers
B. Chain isomers
C. Position isomers
D. Metamers
Answer: A. Functional group isomers
Explanation: Functional isomerism occurs when compounds share the same formula but differ in functional group classes (e.g., ethanol and dimethyl ether).
10. The IUPAC name of CH₃-CH₂-CHO is:
A. Propanal
B. Propanone
C. Propanoic acid
D. Ethyl methyl ketone
Answer: A. Propanal
Explanation: A three-carbon chain containing an aldehyde suffix (-al) is named propanal.
11. Hyperconjugation involves the delocalization of electrons of:
A. C-H σ bond with adjacent empty or partially filled p-orbital
B. π bonds with adjacent π bonds
C. Lone pairs with σ bonds
D. Lone pairs with lone pairs
Answer: A. C-H σ bond with adjacent empty or partially filled p-orbital
Explanation: Also known as Baker-Nathan effect or no-bond resonance, hyperconjugation involves σ(C-H) electron interaction with adjacent p-orbitals.
12. Inductive effect involves complete or partial displacement of:
A. σ (sigma) electrons
B. π (pi) electrons
C. Lone pair electrons
D. Unpaired electrons
Answer: A. σ (sigma) electrons
Explanation: Inductive effect is a permanent displacement of σ-electrons along a carbon chain due to electronegativity differences.
13. Which separation technique is based on difference in boiling points of liquids?
A. Distillation
B. Crystallization
C. Chromatography
D. Sublimation
Answer: A. Distillation
Explanation: Simple distillation separates volatile liquids with sufficient boiling point differences through selective evaporation and condensation.
14. Steam distillation is used to purify substances that are:
A. Steam volatile and insoluble in water
B. Non-volatile and soluble in water
C. Decompose at boiling point and soluble in water
D. Highly soluble in ethanol
Answer: A. Steam volatile and insoluble in water
Explanation: Steam distillation purifies organic compounds like aniline that are immiscible with water and steam-volatile.
15. In Lassaigne's test, nitrogen present in an organic compound is converted to:
A. Sodium Cyanide (NaCN)
B. Sodium Nitrate (NaNO₃)
C. Ammonia (NH₃)
D. Sodium Nitrite (NaNO₂)
Answer: A. Sodium Cyanide (NaCN)
Explanation: Fusion of nitrogenous organic matter with sodium metal yields ionic NaCN (Na + C + N → NaCN).
16. Nitrogen estimation by Kjeldahl's method is NOT applicable to compounds containing:
A. Nitro group (-NO₂) and Azo groups (-N=N-)
B. Primary amines
C. Amides
D. Secondary amines
Answer: A. Nitro group (-NO₂) and Azo groups (-N=N-)
Explanation: Nitrogen in nitro, azo groups, and ring structures (like pyridine) cannot be converted quantitatively to ammonium sulfate in standard digestion.
17. Dumas method is used for the quantitative estimation of:
A. Nitrogen
B. Halogens
C. Carbon and Hydrogen
D. Sulfur
Answer: A. Nitrogen
Explanation: Dumas method estimates total nitrogen by converting organic nitrogen to gaseous N₂ over CuO.
18. Halogens in an organic compound are quantitatively estimated using:
A. Carius method
B. Kjeldahl's method
C. Dumas method
D. Liebig's method
Answer: A. Carius method
Explanation: Carius method heats organic halogens with fuming HNO₃ and AgNO₃ inside a sealed tube to precipitate silver halides (AgX).
19. What is the IUPAC name of HC≡C-CH=CH-CH₃?
A. Pent-3-en-1-yne
B. Pent-2-en-4-yne
C. Pent-1-yn-3-ene
D. Pent-4-yn-2-ene
Answer: A. Pent-3-en-1-yne
Explanation: Numbering starts from the left to give lower locants to unsaturation (triple bond gets 1, double bond gets 3); alkynes rank lower in prefix order, written Pent-3-en-1-yne.
20. Which of the following is a temporary electronic effect operating only in the presence of an attacking reagent?
A. Electromeric effect
B. Inductive effect
C. Resonance effect
D. Hyperconjugation
Answer: A. Electromeric effect
Explanation: Electromeric effect involves temporary complete transfer of shared π-electrons driven by an approaching electrophile or nucleophile.
21. Prussian blue color in Lassaigne's test for nitrogen is due to the formation of:
A. Fe₄[Fe(CN)₆]₃
B. Na₄[Fe(CN)₆]
C. Fe(SCN)₃
D. K₃[Fe(CN)₆]
Answer: A. Fe₄[Fe(CN)₆]₃
Explanation: Iron(III) hexacyanoferrate(II), ferric ferrocyanide Fe₄[Fe(CN)₆]₃, gives the characteristic Prussian blue complex.
22. What is the shape of a carbanion like CH₃⁻?
A. Pyramidal
B. Trigonal planar
C. Linear
D. Octahedral
Answer: A. Pyramidal
Explanation: The carbon atom in a carbanion is sp³ hybridized with three bond pairs and one lone pair, assuming trigonal pyramidal geometry.
23. Which of the following compounds exhibits metamerism?
A. CH₃-O-C₃H₇ and C₂H₅-O-C₂H₅
B. CH₃-CH₂-CH₂-OH and CH₃-CH(OH)-CH₃
C. CH₃-CH₂-COOH and CH₃-CO-OCH₃
D. C₄H₁₀ and C₃H₈
Answer: A. CH₃-O-C₃H₇ and C₂H₅-O-C₂H₅
Explanation: Metamerism arises due to unequal distribution of alkyl chains attached to the same polyvalent functional group (-O-).
24. What is the formula of the functional group present in ketones?
A. >C=O
B. -CHO
C. -COOH
D. -OH
Answer: A. >C=O
Explanation: Ketones contain a carbonyl group (>C=O) bonded to two carbon alkyl or aryl substituents.
25. Chromatography is a physical method used mainly for:
A. Separation, isolation, and purification of components of a mixture
B. Estimating molecular mass
C. Measuring density
D. Determining melting point
Answer: A. Separation, isolation, and purification of components of a mixture
Explanation: Chromatography relies on differential partitioning between stationary and mobile phases to isolate pure compounds.
26. Which group shows -I (negative inductive) effect?
A. -NO₂
B. -CH₃
C. -C₂H₅
D. -(CH₃)₃C
Answer: A. -NO₂
Explanation: Strongly electronegative groups like -NO₂ withdraw σ-electron density, exhibiting a powerful -I effect.
27. Organic compounds having the same general formula and chemical properties but differing by -CH₂- group are called:
A. Homologues
B. Isomers
C. Isotopes
D. Allotropes
Answer: A. Homologues
Explanation: Members of a homologous series share identical functional groups and differ sequentially by a methylene (-CH₂-) unit (14 u).
28. What is the hybridization state of carbon in ethyne (C₂H₂)?
A. sp
B. sp²
C. sp³
D. dsp²
Answer: A. sp
Explanation: Triple-bonded carbons form two σ bonds and two π bonds, requiring sp hybridization with a linear 180° geometry.
29. Purification of solid organic compounds based on solubility differences in a solvent is known as:
A. Crystallization
B. Distillation
C. Sublimation
D. Extraction
Answer: A. Crystallization
Explanation: Crystallization purifies solids by dissolving them in hot solvent and precipitating target crystals upon cooling.
30. What is the IUPAC name of CH₃-CO-CH₃?
A. Propan-2-one
B. Propanal
C. Ethanoic acid
D. Dimethyl ether
Answer: A. Propan-2-one
Explanation: Propan-2-one (acetone) contains 3 carbons with a carbonyl oxygen at position 2.
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