Hydrocarbons Test

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Hydrocarbons Test - 58

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Weekly Quiz Competition

Question 1
1 / -0

An alkane $$C_{7}H_{16}$$ is produced by the reaction of lithium di(3-pentyl)cuprate with ethyl bromide. The name of the product is:

A
3-methylhexane

B
2-ethylpentane

C
3-ethylpentane

D
n-heptane.

Solution

Lithium di(3-pentyl)cuprate is a Gilman reagent. It couples with alkyl halides to give alkanes.
$$\underset{\text{Lithium di(3-pentyl)cuprate}}{[{(C{H}_{3}C{H}_{2})}_{2}CH]_{2}CuLi} + \underset{\text{ethyl bromide}}{BrC{H}_{2}C{H}_{3}} \longrightarrow \underset{3-ethylpentane}{{C}_{2}{H}_{5}-\overset{\underset{|}{{C}_{2}{H}_{5}}}{CH}-{C}_{2}{H}_{5}} + {(C{H}_{3}C{H}_{2})}_{2}CHCu + LiBr$$
Hence the product is 3-ethylpentane.
Question 2
1 / -0

Product A is :

A

B

C

D
Question 3
1 / -0

$$[P]\overset{Br_2}{\longrightarrow}C_2H_4Br_2\overset{NaNH_2}{\underset{NH_3}{\longrightarrow}}Q$$

$$[Q] \overset{20\%H_2SO_4}{\underset{Hg^{2+}, \Delta}{\longrightarrow}}[R]\overset{Zn-Hg/HCl}{\longrightarrow}[S]$$.

The species P, Q, R and S respectively are ___________.

A
Ethene, ethyne, ethanal, ethane

B
Ethane, ethyne, ethanal, ethene

C
Ethene, ethyne, ethanal, ethanol

D
Ethyne, ethane, ethane, ethanol

Solution

$$\underset{[P]}{CH_2=CH_2} \overset{Br_2}{\longrightarrow}Br-CH_2-CH_2-Br\overset{NaNH_2}{\underset{NH_3}{\longrightarrow}}\underset{[Q]}{HC\equiv CH}\overset{HgSO_4}{\underset{Hg^{+2}}{\longrightarrow}}\underset{[R]}{CH_3-CHO}\overset{zn-Hg}{\underset{HCl}{\longrightarrow}}\underset{[S]}{CH_3-CH_3}$$.
Question 4
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Addition of HCl to alkene proceeds in two steps. the first step is the attack of $${H}^{+}$$ ion to $$_{\diagup}^{\diagdown}{C}={C}_{\diagdown}^{\diagup}$$ portion which can be shown as:

A

B

C

D
All are possible

Solution

The arrow represents the direction of electron transefer. In the given reaction, the electron flows from $$\pi$$ bond to electron-deficient group $$H^+$$.

Hence, the correct option is B.
Question 5
1 / -0

In the given reactions:
(i) $$CH_3Br \xrightarrow [ ]{ Na,ether } X \xrightarrow [ hv ]{ Br_2 } Y \xrightarrow [ ]{ Na,ether } Z$$
(ii) $$CH_3COOH \xrightarrow [ ]{ NaOH } X \xrightarrow [ CaO ]{ NaOH } Y \xrightarrow [ hv ]{ Br_2 } Z$$
Identify $$X,\, Y$$ and $$Z$$.

A
$$ (i) X= CH_4;\,\, Y= CH_3Br;\,\, Z= CH_3CH_3\,\,\,\,\,\,(ii) X = CH_3COONa; \,\, Y= CH_3CH_3;\,\, Z = CH_3CH_2Br$$

B
$$ (i) X= CH_3CH_3;\,\, Y= CH_4;\,\, Z= CH_3Br\,\,\,\,\,\,\,(ii) X = CH_3COONa; \,\, Y= CH_3CH_3;\,\, Z = CH_3CH_2CH_3$$

C
$$ (i) X= CH_3CH_2Br;\,\, Y= CH_3CH_3;\,\, Z= CH_3CH_2CH_3\,\,\,\,\,\,\,(ii) X = CH_3COONa; \,\, Y= CH_4;\,\, Z = CH_3Br$$

D
$$ (i) X= CH_3CH_3;\,\, Y= CH_3CH_2Br;\,\, Z= CH_3CH_2CH_2CH_3\,\,\,\,\,\,\,(ii) X = CH_3COONa; \,\, Y= CH_4;\,\, Z = CH_3Br$$

Solution

(i)
(a) When methyl bromide is treated with sodium metal in presence of dry ether, coupling takes place to give ethane. Reaction is known as Wurtz's reaction and also called as coupling reaction of alkyl halide.
$$C{H}_{3}Br \xrightarrow{Na, ether} C{H}_{3}-C{H}_{3}$$
Thus, $$X$$ is $$C{H}_{3}C{H}_{3}$$.
(b)The reaction of ethane with bromine called a substitution reaction.
$$C{H}_{3}-C{H}_{3} \xrightarrow[h \nu]{{Br}_{2}} C{H}_{3}C{H}_{2}Br$$
Thus, $$Y$$ is $$C{H}_{3}C{H}_{2}Br$$.
(c) Next reaction is also Wurtz's reaction and will form butane.
$$C{H}_{3}C{H}_{2}Br \xrightarrow{Na, ether} C{H}_{3}-C{H}_{2}-C{H}_{2}-C{H}_{3}$$
Thus, $$Z$$ is $$C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{3}$$.

(ii)
(a) When $$NaOH$$ added to acetic acid, they react to form sodium acetate and water. This is a typical acid + base neutralization reaction.
$$C{H}_{3}COOH \xrightarrow{NaOH} C{H}_{3}COONa + {H}_{2}O$$
Thus, $$X$$ is $$C{H}_{3}COONa$$.
(b) When sodium acetate is treated with soda lime, decarboxylation takes place and $$CO_2$$ is eliminated from the sodium acetate.
$$C{H}_{3}COONa \xrightarrow[CaO]{NaOH} C{H}_{4} + {Na}_{2}C{O}_{3}$$
Thus, $$Y$$ is $$C{H}_{4}$$.
(c) This reaction between methane and bromine happens in the presence of ultraviolet light - typically sunlight. This is a good example of a photochemical reaction.
$$C{H}_{4} \xrightarrow[h \nu]{{Br}_{2}} C{H}_{3}Br + HBr$$
Thus, $$Z$$ is $$C{H}_{3}Br$$
Question 6
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In the above reaction rate is fastest, when (X) is:

A
-OH

B
$$NH_2$$

C
$$- \overset{O}{\overset{||}{\underset{O}{\underset{||}{S}}}} - OCH_3$$

D
$$- O - \overset{O}{\overset{||}{\underset{O}{\underset{||}{S}}}} - CH_3$$
Question 7
1 / -0

In the following reaction sequence the product B is:

$$Ph-C\equiv CH\xrightarrow [ aq.{ H }_{ 2 }{ SO }_{ 4 } ]{ { Hg }^{ 2+ } } A\xrightarrow [ 2.{ H }_{ 2 }O ]{ 1.{ CH }_{ 3}MgI } B$$

A
$$Ph-CH_3-CH_2-OH$$

B
$$Ph-(CH_3)_2C(OH)$$

C
$$Ph-CH_3-COOH$$

D
none of these

Solution
Question 8
1 / -0

Which of the following method can be used for the preparation of methane?

A
Wurtz reaction

B
Kolbe's reaction

C
Reduction of alkyl halide

D
Hydrogenation of alkene

Solution

Among the given reaction, methane can only be prepared by reduction of alkyl halides.
All other methods prepare ethane as the smallest hydrocarbon.
The preparation of methane by reduction of alkyl halide can be given as follow:

$$CH_3-Cl \xrightarrow[H^+]{Zn}\underset{methane}{CH_4}$$

Hence, the correct option is $$(C)$$.
Question 9
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Correct statement about Kolbe's electrolytic synthesis is:

A
pH of reaction mixture increases as reaction goes on

B
pH of reaction mixture decreases as reaction goes on

C
pH of reaction mixture remain same as reaction goes on

D
pH of reaction mixture first increases and that decreases.

Solution

In Kolbe's electrolytic synthesis, an aqueous solution of sodium or potassium salt of a carboxylic acid on electrolysis give alkane.
The following reaction takes place:
$$2RCOO^-Na^++2H_2O\xrightarrow []{Electrolysis}R-R+2CO_2+H_2+2NaOH$$
As production of alkali i.e. $$NaOH$$ takes place that is why $$pH$$ of reaction mixture increases as reaction goes on.
Question 10
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Which of the following best describes the flow of electrons in the acid- catalyzed dimerization of $$(CH_3)_2C=CH_2$$ ?

A

B

C

D

Solution

(Refer to Image 1)
As $$3^o$$ carbocation is electrophilic in nature and alkene is nucleophilic in nature.
And attack always takes place from electron rich to electron deficient site.
(Refer to Image 2)