CUET UG Chemistry Booster Test -3 Nomenclature and Bond Nature
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QUESTION 1 OF 20
What is the common name for the compound whose IUPAC name is Tetrachloromethane?
QUESTION 2 OF 20
The IUPAC name for the structural formulation (CCl₃)₃CCl is:
QUESTION 3 OF 20
In understanding the stereochemistry of alkyl halides, identifying stereocenters is critical. Which carbon is the asymmetric carbon (stereocenter) in 2-chlorobutane?
QUESTION 4 OF 20
Consider the stereochemical aspects of nucleophilic substitution on chiral alkyl halides:
(I) Sₙ2 reactions are accompanied by an inversion of configuration.
(II) Sₙ1 reactions are accompanied by racemization.
(III) Retention of configuration implies the spatial arrangement of bonds to an asymmetric center is completely preserved.
Which statements are correct?
QUESTION 5 OF 20
Match List-I (Structure) with List-II (Name):
| List-I | List-II |
|---|---|
| 1. p-ClC₆H₄CH₂CH(CH₃)₂ | a. 1-Chloro-4-(2-methylpropyl)benzene |
| 2. m-ClCH₂C₆H₄CH₂C(CH₃)₃ | b. 1-Chloromethyl-3-(2,2-dimethylpropyl)benzene |
| 3. o-Br-C₆H₄CH(CH₃)CH₂CH₃ | c. 1-Bromo-1-(2-bromophenyl)butane |
| 4. CH₃C(p-ClC₆H₄)₂CH(Br)CH₃ | d. 2-Bromo-3,3-bis(4-chlorophenyl)butane |
QUESTION 6 OF 20
Why does electrophilic substitution in haloarenes occur predominantly at ortho- and para-positions despite the halogen's electron-withdrawing inductive effect?
QUESTION 7 OF 20
In the strictly standardized IUPAC system, both geminal (alkylidene) and vicinal (alkylene) dihalides are identically classified and named under the general category of:
QUESTION 8 OF 20
Identify reaction type: The laboratory addition of bromine in CCl₄ to an unknown molecule discharges the reddish-brown color, forming a colourless vic-dibromide. This reaction specifically detects the presence of:
QUESTION 9 OF 20
QUESTION 10 OF 20
QUESTION 11 OF 20
Consider the mechanism of nucleophilic substitution reactions on polarized C-X bonds:
(I) The nucleophile attacks the electron-deficient part of the substrate.
(II) The halogen atom departs as a leaving group (halide ion).
(III) The incoming nucleophile must always possess a positive charge.
Which are analytically accurate?
QUESTION 12 OF 20
Analytically, the C—Cl bond length in haloarenes (169 pm) is shorter than in haloalkanes (177 pm). This bond contraction is fundamentally caused by:
QUESTION 13 OF 20
Based on NCERT values, what is the specific value of the carbon-fluorine (C—F) bond length in pm?
QUESTION 14 OF 20
Arrange the following substrate types in decreasing order of their general bond-cleavage reactivity in an Sₙ1 pathway (based on bond enthalpy and leaving group ability):
| (A) R | Cl |
|---|---|
| (B) R | F |
| (C) R | I |
| (D) R | Br |
QUESTION 15 OF 20
Analytically, despite fluorine being highly electronegative, CH₃Cl possesses a slightly higher dipole moment (1.860 D) than CH₃F (1.847 D). According to general principles, this anomaly is because dipole moment depends on:
QUESTION 16 OF 20
Arrange the following halomethanes in decreasing order of their density (g/mL):
(A) CCl₄
(B) CHCl₃
(C) CH₂Cl₂
QUESTION 17 OF 20
The severe inhibiting effect on the Sₙ2 mechanism caused by the presence of large, bulky alkyl groups near the carbon atom is known as:
QUESTION 18 OF 20
Match List-I (Substrate) with List-II (Preferred Mechanism Pathway):
| List-I | List-II |
|---|---|
| 1. Primary alkyl halide | a. Preferred Sₙ2 pathway due to low steric hindrance |
| 2. Tertiary alkyl halide | b. Preferred Sₙ1 pathway due to high carbocation stability |
| 3. Allylic halide | c. Highly reactive in Sₙ1 due to resonance stabilization (aliphatic C=C adjacent) |
| 4. Benzylic halide | d. Highly reactive in Sₙ1 due to resonance stabilization (aromatic ring adjacent) |
QUESTION 19 OF 20
Arrange the following benzylic bromides in decreasing order of reactivity towards Sₙ1 mechanism:
(A) C₆H₅CH₂Br
(B) C₆H₅CH(C₆H₅)Br
(C) C₆H₅CH(CH₃)Br
(D) C₆H₅C(CH₃)(C₆H₅)Br
QUESTION 20 OF 20
Haloarenes do not generally undergo Sₙ1 reactions under normal conditions because:
Test Complete!
Answer Review
1 What is the common name for the compound whose IUPAC name is Tetrachloromethane?
Tetrachloromethane has formula CCl₄. It contains four chlorine atoms. Common name is carbon tetrachloride.
Tetrachloromethane is a methane derivative in which all four hydrogen atoms are replaced by chlorine atoms. Formula: CCl₄ Its common name is carbon tetrachloride.
- A. Chloroform → Trichloromethane, CHCl₃.
- B. Methylene chloride → Dichloromethane, CH₂Cl₂.
- D. Bromoform → Tribromomethane, CHBr₃.
Used
- Nomenclature Recall
Tetra chloro = Carbon tetrachloride
2 The IUPAC name for the structural formulation (CCl₃)₃CCl is:
The structure contains a heavily chlorinated propane chain. One trichloromethyl group is attached at carbon-2. Correct IUPAC name follows substituted propane nomenclature.
The compound ((CCl₃)₃CCl) contains a central carbon attached to chlorine and three trichloromethyl groups. The correct systematic naming selects the suitable chlorinated propane parent chain and identifies the remaining trichloromethyl substituent. Thus, the correct name is: 2-(Trichloromethyl)-1,1,1,2,3,3,3-heptachloropropane
- B. Decachlorobutane → Oversimplified and not the accepted IUPAC name.
- C. Incorrect parent chain and substituent placement.
- D. Incorrect structural description for the given formula.
Used
- IUPAC Structural Mapping
Find parent chain first, then name substituents.
3 In understanding the stereochemistry of alkyl halides, identifying stereocenters is critical. Which carbon is the asymmetric carbon (stereocenter) in 2-chlorobutane?
C-2 is attached to four different groups. It is bonded to Cl, H, CH₃ and C₂H₅. Therefore, C-2 is the stereocenter.
2-Chlorobutane has the structure: CH₃–CH(Cl)–CH₂–CH₃ Carbon-2 is attached to: H Cl CH₃ CH₂CH₃ Since all four groups are different, C-2 is an asymmetric carbon or stereocenter.
- A. C-1 → Has three hydrogen atoms, not chiral.
- C. C-3 → Attached to two hydrogens, not chiral.
- D. C-4 → Terminal CH₃ carbon, not chiral.
Used
- Stereocenter Identification
Chiral carbon = four different groups
4 Consider the stereochemical aspects of nucleophilic substitution on chiral alkyl halides:
(I) Sₙ2 reactions are accompanied by an inversion of configuration.
(II) Sₙ1 reactions are accompanied by racemization.
(III) Retention of configuration implies the spatial arrangement of bonds to an asymmetric center is completely preserved.
Which statements are correct?
SN2 gives inversion. SN1 gives racemisation. Retention means same configuration is preserved.
SN2 reactions occur by backside attack, causing inversion of configuration. SN1 reactions form a planar carbocation intermediate, so nucleophile can attack from either side, leading to racemisation. Retention of configuration means the spatial arrangement around the chiral center remains unchanged. Therefore, all three statements are correct.
- A, B and C omit one correct statement.
Used
- Statement Verification
SN2 inverts, SN1 racemises
5 Match List-I (Structure) with List-II (Name):
| List-I | List-II |
|---|---|
| 1. p-ClC₆H₄CH₂CH(CH₃)₂ | a. 1-Chloro-4-(2-methylpropyl)benzene |
| 2. m-ClCH₂C₆H₄CH₂C(CH₃)₃ | b. 1-Chloromethyl-3-(2,2-dimethylpropyl)benzene |
| 3. o-Br-C₆H₄CH(CH₃)CH₂CH₃ | c. 1-Bromo-1-(2-bromophenyl)butane |
| 4. CH₃C(p-ClC₆H₄)₂CH(Br)CH₃ | d. 2-Bromo-3,3-bis(4-chlorophenyl)butane |
Para chloro is matched with 1,4-substitution. Meta chloromethyl gives 1,3-substitution. Ortho bromo derivative gives 2-bromophenyl name. Bis chlorophenyl butane matches the complex structure.
The correct structural matches are: 1 → a 2 → b 3 → c 4 → d The para structure corresponds to 1-chloro-4-substitution. The meta structure corresponds to 1,3-substitution. The ortho bromo compound contains a 2-bromophenyl group. The last structure contains two p-chlorophenyl groups and bromobutane skeleton.
- B, C and D mismatch aryl substitution positions and side-chain structures.
Used
- Substituent Position Mapping
o = 1,2; m = 1,3; p = 1,4
6 Why does electrophilic substitution in haloarenes occur predominantly at ortho- and para-positions despite the halogen's electron-withdrawing inductive effect?
Halogens withdraw by –I effect. They donate by resonance. Resonance stabilizes ortho and para intermediates.
Haloarenes are deactivated due to the strong –I effect of halogen. However, halogen also donates lone pair electrons to the benzene ring by resonance. This resonance donation increases electron density at ortho and para positions and stabilizes the corresponding sigma complexes. Therefore, halogens are deactivating but ortho/para directing.
- A. Does not explain ortho/para direction.
- C. Steric blocking is not the main reason.
- D. Haloarenes do not direct exclusively to meta.
Used
- Electronic Effect Analysis
Halogen deactivates but directs o/p
7 In the strictly standardized IUPAC system, both geminal (alkylidene) and vicinal (alkylene) dihalides are identically classified and named under the general category of:
Gem and vic are common classifications. IUPAC names them as dihaloalkanes. Both contain two halogens in alkane chain.
Geminal dihalides have both halogens on the same carbon, while vicinal dihalides have halogens on adjacent carbons. In IUPAC nomenclature, both are named as dihaloalkanes with proper locants.
- A. Dihaloalkenes contain double bonds.
- C. Haloarenes are aromatic halogen compounds.
- D. Alkyl halides usually refer to monohaloalkanes.
Used
- Nomenclature Classification
Two halogens on alkane = dihaloalkane
8 Identify reaction type: The laboratory addition of bromine in CCl₄ to an unknown molecule discharges the reddish-brown color, forming a colourless vic-dibromide. This reaction specifically detects the presence of:
Bromine in CCl₄ detects unsaturation. Alkene decolourises bromine. Product is vic-dibromide.
Bromine in CCl₄ is used to test for carbon-carbon double bonds. Alkenes add bromine across the double bond: C=C + Br₂ → Br–C–C–Br The reddish-brown colour disappears and a colourless vic-dibromide is formed.
- A. Single bonds do not decolourise bromine in CCl₄.
- B. Aromatic rings do not undergo simple bromine addition.
- D. Primary alcohols do not give this test.
Used
- Reaction Test Identification
Br₂/CCl₄ colour loss = C=C present
9
Chiral objects have non-superimposable mirror images. Chiral molecules usually contain stereocentres. They show optical activity.
According to the passage, molecules that are non-superimposable on their mirror images are called chiral. This property is common in molecules containing an asymmetric carbon atom attached to four different groups.
- A. Achiral → Superimposable on mirror image.
- C. Racemic → Equal mixture of two enantiomers.
- D. Symmetrical → Usually achiral.
Used
- Passage Evidence
Chiral = mirror image not superimposable
10
A racemic mixture has equal enantiomers. Their rotations cancel each other. Net optical rotation is zero.
A racemic mixture contains equal amounts of two enantiomers: one rotates plane-polarized light clockwise and the other anticlockwise. Since their rotations are equal and opposite, the total optical rotation becomes zero.
- A. Always positive → Incorrect because rotations cancel.
- B. Always negative → Incorrect because rotations cancel.
- D. Dependent on solvent → Not the deciding factor here.
Used
- Passage Evidence
Racemic = right + left cancel
11 Consider the mechanism of nucleophilic substitution reactions on polarized C-X bonds:
(I) The nucleophile attacks the electron-deficient part of the substrate.
(II) The halogen atom departs as a leaving group (halide ion).
(III) The incoming nucleophile must always possess a positive charge.
Which are analytically accurate?
Nucleophiles attack electron-deficient carbon. Halogen leaves as halide ion. Nucleophiles are electron-rich, not necessarily positive.
In alkyl halides, the C-X bond is polar: Cδ⁺—Xδ⁻ The carbon attached to halogen becomes electron-deficient, so the nucleophile attacks this carbon. During substitution, the halogen leaves as a halide ion. Statement III is incorrect because nucleophiles are electron-rich species. They may be negatively charged or neutral, but they are not always positively charged.
- B. II and III → Statement III is incorrect.
- C. I and III → Statement III is incorrect.
- D. I, II, and III → Includes incorrect Statement III.
Used
- Statement Elimination
Nucleophile = Nucleus-loving, electron-rich
12 Analytically, the C—Cl bond length in haloarenes (169 pm) is shorter than in haloalkanes (177 pm). This bond contraction is fundamentally caused by:
sp² carbon has more s-character than sp³ carbon. It holds electrons more tightly. Haloarene C—Cl bond becomes shorter.
In haloarenes, the halogen is bonded to an sp² hybridized carbon of the benzene ring. An sp² carbon has greater s-character than an sp³ carbon. Greater s-character makes the carbon more electronegative and allows it to hold the C—Cl bond pair more tightly. Also, resonance gives partial double bond character to the C—Cl bond, further shortening it.
- B. Lack of resonance → Incorrect; resonance is present.
- C. Steric hindrance is not the fundamental cause of shorter bond length.
- D. Halogen is not described by sp³ hybridization in this context.
Used
- Hybridisation Analysis
More s-character = shorter, stronger bond
13 Based on NCERT values, what is the specific value of the carbon-fluorine (C—F) bond length in pm?
Fluorine is the smallest halogen. C—F bond is the shortest C—X bond. Its bond length is 139 pm.
Among carbon-halogen bonds, C—F is the shortest because fluorine has the smallest atomic size. NCERT value: C—F bond length = 139 pm
| • B. 178 → Approximate C | Cl bond length. |
|---|---|
| • C. 193 → Approximate C | Br bond length. |
| • D. 214 → Approximate C | I bond length. |
Used
- Data Recall
F is smallest, C—F = 139 pm
14 Arrange the following substrate types in decreasing order of their general bond-cleavage reactivity in an Sₙ1 pathway (based on bond enthalpy and leaving group ability):
| (A) R | Cl |
|---|---|
| (B) R | F |
| (C) R | I |
| (D) R | Br |
SN1 involves C—X bond cleavage. Iodide is the best leaving group. Fluoride is the poorest leaving group.
In SN1 reactions, the first slow step is cleavage of the C—X bond. Leaving group ability follows: I⁻ > Br⁻ > Cl⁻ > F⁻ Bond enthalpy decreases in the order: C—F > C—Cl > C—Br > C—I So C—I cleaves most easily and C—F cleaves least easily. Therefore, decreasing SN1 reactivity is: R—I > R—Br > R—Cl > R—F Hence: (C), (D), (A), (B)
- B, C and D do not follow leaving-group ability or bond enthalpy trends.
Used
- Leaving Group Analysis
I leaves first, F leaves last
15 Analytically, despite fluorine being highly electronegative, CH₃Cl possesses a slightly higher dipole moment (1.860 D) than CH₃F (1.847 D). According to general principles, this anomaly is because dipole moment depends on:
Dipole moment depends on charge and distance. C—Cl bond is longer than C—F. This makes CH₃Cl slightly more polar in dipole value.
Dipole moment is calculated as: μ = q × r where: q = magnitude of charge separation r = internuclear distance Although C—F has greater charge separation due to fluorine's high electronegativity, the C—F bond is very short. The C—Cl bond has slightly less charge separation but a longer bond length, giving CH₃Cl a slightly higher dipole moment than CH₃F.
- A. Only charge separation → Incomplete; distance also matters.
- B. Only bond length → Incomplete; charge separation also matters.
- D. Atomic mass of carbon → Not related to dipole moment.
Used
- Dimensional/Concept Analysis
Dipole moment = charge × distance
16 Arrange the following halomethanes in decreasing order of their density (g/mL):
(A) CCl₄
(B) CHCl₃
(C) CH₂Cl₂
Density increases with the number of chlorine atoms. CCl₄ is the heaviest among the given compounds. CH₂Cl₂ has the lowest density among these.
Among halomethanes, increasing chlorine content generally increases molecular mass and density. CCl₄ has four chlorine atoms, CHCl₃ has three chlorine atoms, and CH₂Cl₂ has two chlorine atoms. Therefore, decreasing order of density is: CCl₄ > CHCl₃ > CH₂Cl₂ So the correct order is: (A), (B), (C)
- B → Gives reverse order.
- C → Places CHCl₃ above CCl₄ incorrectly.
- D → Places CH₂Cl₂ above CHCl₃ incorrectly.
Used
- Molecular Mass Trend Analysis
More Cl atoms = Higher density
17 The severe inhibiting effect on the Sₙ2 mechanism caused by the presence of large, bulky alkyl groups near the carbon atom is known as:
Bulky groups block nucleophile approach. SN2 requires backside attack. This blocking effect is steric hindrance.
In Sₙ2 reactions, the nucleophile must approach the carbon bearing the leaving group from the backside. Large bulky alkyl groups around or near this carbon obstruct the nucleophile's approach. This spatial blocking effect is called steric hindrance. This is why tertiary alkyl halides are very slow or unreactive in Sₙ2 reactions.
- A → Inductive effect deals with electron donation or withdrawal, not physical blocking.
- B → Resonance stabilization affects intermediate stability, mainly in Sₙ1.
- D → Racemization is an optical effect commonly linked with Sₙ1 reactions.
Used
- Mechanism-Based Concept Identification
Steric = Space blocking
18 Match List-I (Substrate) with List-II (Preferred Mechanism Pathway):
| List-I | List-II |
|---|---|
| 1. Primary alkyl halide | a. Preferred Sₙ2 pathway due to low steric hindrance |
| 2. Tertiary alkyl halide | b. Preferred Sₙ1 pathway due to high carbocation stability |
| 3. Allylic halide | c. Highly reactive in Sₙ1 due to resonance stabilization (aliphatic C=C adjacent) |
| 4. Benzylic halide | d. Highly reactive in Sₙ1 due to resonance stabilization (aromatic ring adjacent) |
Primary halides favor Sₙ2. Tertiary halides favor Sₙ1. Allylic and benzylic halides form resonance-stabilized carbocations.
Primary alkyl halides have low steric hindrance, so they favor Sₙ2 reactions. Tertiary alkyl halides form stable tertiary carbocations, so they favor Sₙ1 reactions. Allylic halides form allylic carbocations stabilized by resonance with a C=C bond. Benzylic halides form benzylic carbocations stabilized by resonance with an aromatic ring. Correct matching: 1-a, 2-b, 3-c, 4-d
- B, C and D incorrectly match substrate types with unsuitable reaction pathways.
Used
- Concept Mapping
Primary = Sₙ2; Tertiary = Sₙ1; Allylic/Benzylic = Resonance
19 Arrange the following benzylic bromides in decreasing order of reactivity towards Sₙ1 mechanism:
(A) C₆H₅CH₂Br
(B) C₆H₅CH(C₆H₅)Br
(C) C₆H₅CH(CH₃)Br
(D) C₆H₅C(CH₃)(C₆H₅)Br
Sₙ1 rate depends on carbocation stability. More resonance and alkyl stabilization increases reactivity. Compound D forms the most stable carbocation.
In Sₙ1 reactions, the rate-determining step is carbocation formation. Carbocation stability order: C₆H₅C(CH₃)(C₆H₅)⁺ > C₆H₅CH(C₆H₅)⁺ > C₆H₅CH(CH₃)⁺ > C₆H₅CH₂⁺ Reason: D is stabilized by two phenyl groups and one methyl group. B is stabilized by two phenyl groups. C is stabilized by one phenyl and one methyl group. A is stabilized by only one phenyl group. Therefore, decreasing Sₙ1 reactivity: (D), (B), (C), (A)
- B → Gives nearly reverse order.
- C → Places C above B incorrectly.
- D → Places B above D incorrectly.
Used
- Carbocation Stability Comparison
More phenyl groups = more resonance = faster Sₙ1
20 Haloarenes do not generally undergo Sₙ1 reactions under normal conditions because:
Sₙ1 requires carbocation formation. Phenyl cation is extremely unstable. Haloarenes resist Sₙ1 reactions.
For an Sₙ1 reaction, the substrate must ionize to form a carbocation. In haloarenes, cleavage of the C—X bond would generate a phenyl cation. This phenyl cation is highly unstable and is not stabilized by resonance in the usual way. Also, the aryl C—X bond has partial double bond character, making cleavage difficult. Thus haloarenes do not generally undergo Sₙ1 reactions under normal conditions.
- A → Haloarenes involve sp² carbon, not sp³ carbon.
- C → Bulky phenyl ring does not promote nucleophilic attack.
- D → Halogens do not perfectly stabilize the phenyl cation.
Used
- Intermediate Stability Analysis
Haloarene Sₙ1 fails because phenyl cation is unstable
