General Organic Chemistry MCQ Questions & Answers in Organic Chemistry | Chemistry
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81.
Which of the following cannot be represented by resonance structures ?
A
Dimethyl ether
B
Nitrate anion
C
Carboxylate anion
D
Toluene
Answer :
Dimethyl ether
Ethers due to absence of delocalized pair of electrons do not show resonance.
82.
Which of the following IUPAC names is not correctly matched?
A - Cyclopentane
B - Chlorocyclohexane
C - 1, 1-dimethylcyclohexane
D -3-Nitrocyclohexene
Answer : - 1, 1-dimethylcyclohexane
No explanation is given for this question. Let's discuss the answer together.
83.
The change in the state of hybridization of the asterisked carbon in the following reaction.
\[C{{H}_{3}}\overset{*}{\mathop{C}}\,N\xrightarrow{{{H}_{2}}O}C{{H}_{3}}\overset{*}{\mathop{C}}\,ON{{H}_{2}}\] is
A
$$s{p^3}\,{\text{to}}\,s{p^2}$$
B
$$s{p^3}\,{\text{to}}\,sp$$
C
$$sp\,{\text{to}}\,s{p^2}$$
D
$$s{p^2}\,{\text{to}}\,s{p^3}$$
Answer :
$$sp\,{\text{to}}\,s{p^2}$$
84.
How many stereoisomers does this molecule have?
$$C{H_3}CH = CHC{H_2}CHBrC{H_3}$$
A
4
B
6
C
8
D
2
Answer :
4
$${C^*} = $$ asymmetric carbon
Number of optical isomers $$ = {2^n}$$
where, $$n = $$ number of asymmetric carbon atoms $$ = {2^1} = 2$$
Number of geometrical isomers $$ = {2^n}$$
where, $$n = $$ number of double bonds $$ = {2^1} = 2$$
Hence, total number of stereoisomers = Total optical isomers + Total geometrical isomers = 2 + 2 = 4
85.
Which of the following is the correct order of acidity of carboxylic acids?
$$\left( {\text{i}} \right)C{l_3}CCOOH > C{l_2}CHCOOH$$ $$ > ClC{H_2}COOH$$
$$\left( {{\text{ii}}} \right)C{H_3}C{H_2}COOH > $$ $${\left( {C{H_3}} \right)_2}CHCOOH > {\left( {C{H_3}} \right)_3}CCOOH$$
$$\left( {{\text{iii}}} \right){F_2}CHCOOH > FC{H_2}COOH$$ $$ > ClC{H_2}COOH$$
A
(i) and (ii)
B
(ii) and (iii)
C
(i) and (iii)
D
(i), (ii) and (iii)
Answer :
(i), (ii) and (iii)
The strength of the acid increases with the inductive effect of the electronegative group attached to it ( $$-I$$ effect ). The strength of the acid decreases with the presence of electron releasing group.
86.
Out of the following compounds, which will have a zero
dipole moment?
A
1, 1 - dichloroethylene
B
$$cis$$ - 1, 2 - dichloroethylene
C
$$trans$$ - 1, 2 - dichloroethylene
D
None of these compounds
Answer :
$$trans$$ - 1, 2 - dichloroethylene
[ Note : dipole moment is a vector quantity ].
87.
Arrange in the order of increasing acidity.
A
III < I < II
B
I < III < II
C
III < II < I
D
II < I < III
Answer :
II < I < III
Order of Acidic strength $$ \propto $$ stability of conjugate base.
88.
Select the most stable carbocation amongst the following
A
B
C
D
Answer :
Structure (B) is a $${3^ \circ }$$ carbocation, while (A) is $${2^ \circ }$$ and (C) and (D) are $${1^ \circ }$$ carbocations; thus (B) is the most stable.
89.
Which of the following orders is correct for heat of hydrogenation of these compounds ?
A
I > II > III
B
III > II > I
C
II > III > I
D
III > I > II
Answer :
II > III > I
$${\text{Heat of hydrogenation}} \propto \frac{1}{{{\text{Stability of alkene}}}}.$$
90.
The masses of carbon, hydrogen and oxygen in an organic compound are in the ratio 6 : 1 : 8 respectively. Which of the following pairs of formulae correspond to above information?
A
$$C{H_2}O{\text{ and }}C{H_3}CHO$$
B
$$C{H_2}O{\text{ and }}{C_3}{H_6}O$$
C
$${C_3}{H_6}O{\text{ and }}{C_2}{H_6}{O_2}$$
D
$${C_3}{H_6}{O_3}{\text{ and }}HCHO$$
Answer :
$${C_3}{H_6}{O_3}{\text{ and }}HCHO$$
In $${C_3}{H_6}{O_3},$$ mass of 3 $$C$$ - atoms = 12 × 3 = 36
mass of 6 $$H$$ - atoms = 1 × 6 = 6
mass of 3 $$O$$ - atoms = 16 × 3 = 48
∴ Ratio of masses of $$C : H : O$$ is 36 : 6 : 48 or 6 : 1 : 8.
In $$HCHO,$$ mass of 1 $$C$$ - atom = 12
mass of 2 $$H$$ - atoms = 2
mass of 1 $$O$$ - atom = 16
∴ Ratio of masses of $$C : H : O$$ is 12 : 2 : 16 or 6 : 1 : 8.