Hydrocarbons Test

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Hydrocarbons Test - 71

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Weekly Quiz Competition

Question 1
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Intermediate in hydration of alkene is

A
Free radical

B
Carbene

C
Carbonium ion

D
Carbanion

Solution

Option C is correct.
Question 2
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Directions For Questions

Hydrogenation of alkenes and alkynes takes place in presence of certain catalysts. In Sabatier Senderen's reaction, the addition of hydrogen takes place in the presence of Raney nickel catalyst. Platinum and palladium can also be used as a catalyst in these reactions. These are the heterogeneous catalyst and used in a finely divided state. Experimentally, it is observed that less crowded alkenes adsorb $$H_{2}$$ at a faster rate. Controlled hydrogenation of alkyne in the presence of Lindlar's catalyst yields cis product i.e., 'cis' alkene. Thus, in the presence of Lindlar's catalyst, 'syn' addition takes place. The relative rate of hydrogenation follows the order:
$$-C \equiv C - >\ \ >C= C<\ \ > \ \ > C = O > C_{6}H_{6}$$
Non-terminal alkynes a reduced in presence of $$Na$$ or $$Li$$ metal dissolved in liquid ammonia. In this reaction, the anti-addiction of hydrogen results in the trans-product.
Answer the following questions:

...view full instructions

The relative rate of catalytic hydrogenation of following alkenes is

A
$$II > III > IV > I$$

B
$$I > IV > III > II$$

C
$$III > IV > I > II$$

D
$$II > IV > I > III$$
Solution
$$concept: \text{less crowded alkenes adsorb }H_2\text{ with faster rate.}$$

from the question
$$I\rightarrow $$ tetra substituted alkene
$$II\rightarrow $$ mono substituted alkene
$$III\rightarrow $$ di substituted alkene
$$IV\rightarrow $$ tri substituted alkene
Thus, the relative rate of catalytic hydrogenation of the given alkenes is

$$II>III>IV>I$$ $$(\because \text{less the substitution, less will be crowding and more will be the rate.})$$

Option A is correct.
Question 3
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In the given reaction,
$$CH_{3} - CH\equiv C - CH_{3} \xrightarrow {Na/NH_{3}(liq.)}X$$
Compound $$(X)$$ will be

A
Butane

B
$$Trans-2-butene$$

C
$$Cis-2-butene$$

D
$$1-butene$$

Solution

Question 4

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Match List - I with List-II and select the correct answer from the codes given below the lists:

	List I Reaction		List II Product
A.	$$CH_{3}CH = CH_{2} \underset {(ii)HCOOH}{\xrightarrow {(i) BH_{3}-THF}}$$	1.	$$n-propylamine$$
B.	$$CH_{3}CH = CH_{2} \xrightarrow {(ii) AgNO_{3}}{\xrightarrow {(i) BH_{3} - THF}}$$	2.	$$n-propylbromide$$
C.	$$CH_{3}CH = CH_{2} \underset {(ii) Br_{2}}{\xrightarrow {(i) BH_{3} - THF}}$$	3.	$$n-hexane$$
D.	$$CH_{3}CH = CH_{2} \underset {(ii) Br_{2}}{\xrightarrow {(i) BH_{3} - THF}}$$	4.	$$n-propane$$

$$A = 1, B = 2, C = 3, D = 4$$

$$A = 2, B = 1, C = 4, D = 3$$

$$A = 3, B = 4, C = 2, D = 1$$

$$A = 4, B = 3, C = 1, D = 2$$

Solution

Question 5
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The compound prepared by a substitution reaction of benzene is:

A
Acetophenone

B
Glyoxal

C
Cyclohexane

D
Hexabromocyclohexane

Solution
Question 6
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Disubstituted derivatives of benzene are of ________ type/ types.

A
$$1$$

B
$$2$$

C
$$3$$

D
$$6$$

Solution
Question 7
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The number of $$\pi-electrons$$ in benzene molecule are:

A
$$6$$

B
$$3$$

C
$$5$$

D
$$4$$

Solution

It can be determined by the Huckel's Rule (4n+2 rule):

In order to be aromatic, a molecule must have a certain

number of pi electrons (electrons with pi bonds, or lone

pairs within p orbitals) within a closed loop of parallel,

adjacent p orbitals.

For benzene, there is 1 aromatic compound .

Then n = 1

From Huckel’s rule

Number of pi electrons = 4n + 2

=4x1 + 2

= 6

The number of π−electronsπ−electrons in benzene

molecule is 6.

Since, Option A is correct.
Question 8
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Benzene gives mainly:

A
Substitution reaction

B
Addition reaction

C
Elimination reaction

D
All of these

Solution

Benzene is much more stable than expected.

The extra stability means that benzene will less

readily undergo addition reactions. In benzene,

the π-electrons are delocalised and makes the

structure more stable. Thus, benzene does not

give addition reactions because of resonance

stabilisation.

The more loosely held electrons are open to attack by

electrophiles. Hence, the characteristic reaction

of benzene is electrophilic substitution.

Example: Nitration and Suphonation of Benzene.

So it does not undergo Elimination reaction.

Since, option A is correct.
Question 9
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The ring structure of benzene was first proposed by:

A
Wohler

B
Faraday

C
Kekule

D
Baeyer

Solution

Question is a fact.

Since, Option C is correct.
Question 10
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The most appropriate major product of the above sequence of reaction would be:

A

B

C

D

Solution