Hydrocarbons Test

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Hydrocarbons Test - 19

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Weekly Quiz Competition

Question 1
1 / -0

The reaction least likely to occur is:

A

B

C

D

Solution

In the presence of ultraviolet light (but without a catalyst present), hot benzene will also undergo an addition reaction with chlorine or bromine. The ring delocalization is permanently broken and a chlorine or bromine atom adds on to each carbon atom.
$$C_6H_6 + Cl_2\xrightarrow{heat} C_6H_5Cl$$.
Question 2
1 / -0

The increasing order of stability of the following free radicals is:

A
$$(CH_2)_2\, \dot{C}H\, <\, (CH_3)_3\, \dot{C}\, <\, (C_6H_5)_2\, \dot{C}H\, <\, (C_6H_5)_3\, \dot{C}$$

B
$$(C_6H_5)_2\, \dot{C}\, <\, (C_6H_5)_2\, \dot{C}H\, <\, (CH_3)_3\, \dot{C}\, <\, (CH_3)_2\, \dot{C}H$$

C
$$(C_6H_5)_2\, \dot{C}H\, <\, (C_6H_5)_3\, \dot{C}H\, <\, (CH_3)_3\, \dot{C}\, <\, (CH_3)_2\, \dot{C}H$$

D
$$(CH_3)_2\, \dot{C}H\, <\, (CH_3)_3\, \dot{C}\, <\, (C_6H_5)_3\, \dot{C}H\, <\, (C_6H_5)_2\, \dot{C}H$$

Solution
Question 3
1 / -0

Which of the following catalysts is/are used for partial reduction of alkyne?

A
$$Ni$$

B
$$Ni_2B$$ or P-2 catalyst

C
Lindlar catalyst

D
None of these

Solution

Lindlar's catalyst is used for partial reduction of alkyne. Lindlar's catalyst is a mixture of lead, calcium carbonate, lead salts and quinoline.
Question 4
1 / -0

The ease of formation of free radicals follows the order:

A
$$3^o > 2^o > 1^o > \overset {\cdot}{C}H_3$$

B
$$\overset {\cdot}{C}H_3 > 1^o > 2^o > 3^o$$

C
$$1^o > 2^o > 3^o > \overset {\cdot}{C}H_3$$

D
$$2^o > 1^o > 3^o > \overset {\cdot}{C}H_3$$

Solution

Hyperconjugation inverse is the stability of the free radical and that’s why loss of free radical is the highest.
Question 5
1 / -0

The least reactive alkane towards free-radical substitution reactions is:

A
$$CH_4$$

B
$$(CH_3)_3CH$$

C
$$CH_3CH_3$$

D
$$CH_3CH_2CH_3$$

Solution

Methane is less reactive towards free-radical mechanism as it has only one carbon and no substituted alkyl group. Thus it does not have extra carbon atom to make free radical.
Question 6
1 / -0

Equal weights $${C}_{2}{H}_{6}$$ and hydrogen are mixed in an empty container at $${0}^{o}C$$. The fraction of total pressure exerted by hydrogen is-

A
$$1:2$$

B
$$1:1$$

C
$$1:16$$

D
$$15:16$$

Solution

Consider x gm be the weight of $$C_{2}H_{6}$$ and hydrogen.
No. of moles of hydrogen = x/2
No. of moles of $$C_{2}H_{6}$$ = x/30
Mole fraction of hydrogen =( x/2)/(x/2+x/30) = 15/16
The pressure exerted by hydrogen = mole fraction of hydrogen * total pressure
= 15/16 * 1 = 15/16
Question 7
1 / -0

2-Methyl butane on reacting with bromine in the presence of sunlight gives mainly:

A
1-Bromo-3-methylbutane

B
1-Bromo-2-methylbutane

C
2-Bromo-3-methylbutane

D
2-Bromo-2-methylbutane

Solution

D. 2-Bromo-2-methyl butane-22%
The bromination has 4 products in terms of substitution of hydrogen atom at same rate.
2-Bromo-2-methyl butane(22%/1=22%)
2-Bromo-3-methyl butane(33%/2=16.5%)
1-Bromo-2-methyl butane(30%/6=5%)
1-Bromo-3-methyl butane(15%/3=5%)
Question 8
1 / -0

l-bromo-3-chloro cyclobutane will react with two moles of Na in ether producing:

A

B

C

D

Solution

The compound 1-bromo-3-chloro undergoes Wurtz synthesis when it reacts with 2 moles of Na producing a hydrocarbon. The product obtained is as shown in option A.
Question 9
1 / -0

Which one of the following compound will give addition reaction?

A
$$\displaystyle { CH }_{ 4 }$$

B
$$\displaystyle { C }_{ 2 }{ H }_{ 6 }$$

C
$$\displaystyle { C }_{ 2 }{ H }_{ 4 }$$

D
$$\displaystyle { C }_{ 3 }{ H }_{ 8 }$$

Solution

$$\displaystyle { CH }_{ 4 }$$, $$\displaystyle { C }_{ 2 }{ H }_{ 6 }$$ and $$\displaystyle { C }_{ 3 }{ H }_{ 8 }$$ are saturated hydrocarbons.
Hence, they will give substitution reaction.

$$\displaystyle { C }_{ 2 }{ H }_{ 4 }$$ on the other hand is an unsaturated hydrocarbon.
It will give addition reaction.

For example, catalytic hydrogenation of ethylene gives ethane. A molecule of hydrogen is added across $$C=C$$ double bond.
$$\displaystyle { C }_{ 2 }{ H }_{ 4 } + H_2 \xrightarrow {Ni/Pt/Pd} \displaystyle { C }_{ 2 }{ H }_{ 6 }$$
Question 10
1 / -0

In an alkane if the value of n = 19, it is:

A
solid

B
liquid

C
gaseous

D
none of the above

Solution

The homologous of alkanes larger than hexadecane are solids, solid alkanes are normally soft, with low melting points. These characteristics are due to strong repulsive forces generated between electrons on neighboring atoms, which are in close proximity in crystalline solids. The strong repulsive forces counterbalance the weak van der Waals forces of attraction, alkanes are almost completely insoluble in water. If n=19, then the alkane $$C_{19}H_{40}$$ is a solid.