Hydrocarbons — DPP 1

20 NEET questions from Hydrocarbons, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

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1
$\mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { CH } _ { 2 } \mathrm { CH } _ { 2 } \mathrm { CH } _ { 3 }$ is when oxidised in the presence of alk. $\mathrm { KMnO } _ { 4 }$, the product obtained is
  1. A $\mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { CHO }$
  2. B $\mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { COOH }$
  3. C $\mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { CH } _ { 2 } \mathrm { CH } _ { 2 } \mathrm { CHO }$
  4. D $\mathrm { C } _ { 6 } \mathrm { H } _ { 5 } \mathrm { COCH } _ { 3 }$
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Correct answer: B

Hydrocarbons – NEET-14301 Alkaline $\mathrm{KMnO}_{4}$ is a strong oxidizing agent and oxidizes alkyl benzenes to benzoic acid.
2
The compound A is
Hydrocarbons – NEET-14339
  1. A
  2. B
  3. C
  4. D
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Correct answer: B

Hydrocarbons – NEET-14339
3
The angle strain in cyclopentane is
  1. A $72 ^ { \circ }$
  2. B $1 ^ { \circ } 28 ^ { \prime }$
  3. C $44 ^ { \prime }$
  4. D $108 ^ { \circ }$
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Correct answer: C

Angle strain ∝ d = $\frac{1}{2}$(109.5 - α)
= $\frac{1}{2}$(109°28' - 108°)
[for cyclopentane a = 108° a = inner angle]
= $\frac{1^{\circ} 28^{\prime}}{2}$ = 44'
4
Hydrocarbons – NEET-14395
  1. A $\mathrm { CH } _ { 3 } - \mathrm { CH } = \mathrm { CH } - \mathrm { CH } _ { 3 }$
  2. B $\mathrm { CH } _ { 2 } = \mathrm { CH } - \mathrm { CH } _ { 2 } - \mathrm { CH } _ { 3 }$
  3. C
  4. D Both (B) & (C)
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Correct answer: B

Hydrocarbons – NEET-14395
5
In Kharash effect; reaction follows
  1. A Free radical substitution
  2. B Electrophilic addition
  3. C Free radical addition
  4. D Nucleophilic addition
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Correct answer: C

Kharasch effect is the anti-Markovnikov's addition of HBr to an unsymmetrical alkene in the presence of peroxide. This reaction follows free radical addition.
Hydrocarbons – NEET-14401
6
Eclipsed form of ethane has higher energy due to
  1. A Torsional strain
  2. B Steric strain
  3. C Angle strain
  4. D Both (A) and (B)
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Correct answer: D

The eclipsed form of ethane possess higher energy and hence unstable. This is due to the torsional strain and steric strain due to the repulsion between the electron clouds of the C-H bond.
7
In the following compounds the decreasing order of B.P. is
(I) $\mathrm { CH } _ { 3 } - \mathrm { CH } _ { 2 } - \mathrm { CH } _ { 2 } - \mathrm { CH } _ { 2 } - \mathrm { CH } _ { 2 } - \mathrm { CH } _ { 3 }$,
Hydrocarbons – NEET-14197
  1. A (I) $>$ (II) $>$ (III)
  2. B (I) $>$ (III) $>$ (II)
  3. C (II) $>$ (III) $>$ (I)
  4. D (III) $>$ (II) $>$ (I)
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Correct answer: A

With increase in branching boiling point decreases. This is due to decrease in the magnitude of van der Waals forces with increase in branching. Therefore boiling point of $n$-hexane is higher than 2-methyl pentane and 2,2-dimethylbutane.
8
Hydrocarbons – NEET-14402
  1. A
  2. B
  3. C
  4. D
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Correct answer: A

Hydrocarbons – NEET-14402 Hydroboration oxidation results in the anti-Markovnikov's addition of water to alkene.
9
Addition of HBr to 2-methyl-1-propene in the presence of hydrogen-peroxide produces
  1. A 1-Bromobutane
  2. B 2-Bromopropane
  3. C 2-Bromo-2-methylpropane
  4. D 1-Bromo-2-methylpropane
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Correct answer: D

Mechanism
Hydrocarbons – NEET-14400
10
What is X in the following sequence of reactions?
$\mathrm { X } \xrightarrow [ - 1 / 2 \mathrm { H } _ { 2 } ] { \mathrm { Na } } \mathrm { Z } \xrightarrow { \mathrm { NaOH } / \mathrm { CaO } } \mathrm { CH } _ { 4 }$
  1. A Methane
  2. B Ethanoic acid
  3. C Propane
  4. D Ethene
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Correct answer: B

$\mathrm{CH}_{3} \mathrm{COOH} \xrightarrow[-1 / 2 \mathrm{H}_{2}]{\mathrm{Na}} \mathrm{CH}_{3} \mathrm{COONa} \xrightarrow[\text { Decarboxylation }]{\mathrm{NaOH} / \mathrm{CaO}} \mathrm{CH}_{4}+\mathrm{Na}_{2} \mathrm{CO}_{3}$
11
The minimum heat of hydrogenation is in
Hydrocarbons – NEET-14338
  1. A (A)
  2. B (B)
  3. C Both have equal
  4. D Cannot predict
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Correct answer: A

Hydrocarbons – NEET-14338 Trans 2-butene will show minimum heat of hydrogenation because trans 2-butene is more stable as compared to cis 2-butene.
12
Addition of HBr to propene
  1. A Follows Markownikov's rule
  2. B Does not follow Markowinkov's rule
  3. C Follows Markownikov's rule but the product rearranges to give anti-Markownikov's product
  4. D Follows free radical mechanism
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Correct answer: A

Hydrocarbons – NEET-14399When HBr is adds to propene, Markovnikov's rule is obeyed. However in the presence of peroxide, free radical addition of HBr to propene takes place which does not follow Markovnikov's rule.
13
Which one of the following statement is not correct for sigma- and pi-bonds formed between two carbon atoms?
  1. A Sigma-bond is stronger than a pi-bond
  2. B Bond energies of sigma- and pi-bonds are of the order of $264 \mathrm {~kJ} / \mathrm { mol }$ and $347 \mathrm {~kJ} / \mathrm { mol }$, respectively
  3. C Free rotation of atoms about a sigma-bond is allowed but not in case of a pi-bond
  4. D Sigma-bond determines the direction between carbon atoms but a pi-bond has no primary effect in this regard
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Correct answer: B

The bond energy of sigma bond is about $397 \mathrm{~kJ} / \mathrm{mol}$, where as the bond energy for pi bond is about $284 \mathrm{~kJ} /$ mol sigma bond is stronger than pi bond.
14
In iodination; for preparation of iodomethane compound used is
  1. A $\mathrm { HIO } _ { 3 }$
  2. B HgO
  3. C Both (A) & (B)
  4. D HI
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Correct answer: C

Both $\mathrm{HNO}_{3}$ and HgO can be used for preparation of iodomethane because these oxidizes the HI formed as one of the product to shift the reaction in the forward direction
$\mathrm{CH}_{4}+\mathrm{I}_{2} \stackrel{\Delta}{\rightleftharpoons} \mathrm{CH}_{3} \mathrm{I}+\mathrm{HI}$
15
The reaction of $\mathrm { CH } _ { 3 } \mathrm { CH } = \mathrm { CH } _ { 2 }$ with HOCl will yield
  1. A 2-chloro-1-propanol
  2. B 3-chloro-2-propanol
  3. C 1-chloro-2-propanol
  4. D 1-chloro-1-propanol
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Correct answer: C

Hydrocarbons – NEET-14398
16
Hydrocarbons – NEET-14234 The compound " A " is
  1. A
  2. B
  3. C
  4. D
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Correct answer: A

Mechanism
$\mathrm{Cl}_{2} \xrightarrow{\mathrm{hv}} 2 \dot{\mathrm{Cl}}$
Hydrocarbons – NEET-14234 Selectivity for $\mathrm{Cl}_{2}$ is $1: 3.8: 5$ for $1^{\circ}: 2^{\circ}: 3^{\circ}$
17
Which one is most stable?
  1. A Cyclopropane
  2. B Cyclobutane
  3. C Cyclopentane
  4. D Cyclohexane
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Correct answer: D

Cyclohexane is most stable because the ring is not planar but it is puckered in which all angles are tetrahedral and thus cyclohexane ring is stainless.
18
Hydrocarbons – NEET-14233 can be prepared by
  1. A Wurtz reaction
  2. B Fittig reaction
  3. C Wurtz-Fittig reaction
  4. D Frankland reaction
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Correct answer: C

The reaction of an aromatic halide with aliphatic halide in presence of Na and dry ether to give alkyl benzenes is called Wurtz fittig reaction
Hydrocarbons – NEET-14233

19
Hydrocarbons – NEET-14403
  1. A
  2. B
  3. C
  4. D
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Correct answer: B

Hydrocarbons – NEET-14403
20
In which alkane isomerization will not occur?
  1. A $\mathrm { C } _ { 2 } \mathrm { H } _ { 6 }$
  2. B $\mathrm { C } _ { 4 } \mathrm { H } _ { 10 }$
  3. C $\mathrm { C } _ { 5 } \mathrm { H } _ { 10 }$
  4. D $\mathrm { C } _ { 6 } \mathrm { H } _ { 14 }$
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Correct answer: A

In ethane, isomerization is not possible because it contains only two carbon atoms
Hydrocarbons – NEET-14291

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