Which one of the following compounds does not decolourize bromine water?
A.
B.
C.
D.
Correct Answer: C
Explanation:
Test for unsaturation i.e. Bromine water Reddish orange colour of bromine solution in $\mathrm{CCl}_4$ will discharge when bromine adds to an unsaturation site.
An alkene “A” on reaction with O3 and Zn + H2O gives propanone and ethanal in equimolar ratio. Addition
of HCl to alkene “A” gives “B” as the major product. The structure of product “B” is :
It is also true that 2$^\circ$ free radical is more stable
than 1$^\circ$ free radical but it is not the answer of the
given assertion. Thus, both assertion and reason
are true but reason is not the correct answer for
the given assertion.
Hydrocarbon (A) reacts with bromine by
substitution to form an alkyl bromide which by
Wurtz reaction is converted to gaseous
hydrocarbon containing less than four carbon
atoms. (A) is
I. $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CHCH}_3$ (major product)
II. $\mathrm{CH}_2=\mathrm{CHCH}_2 \mathrm{CH}_3$ (minor product)
A.
Saytzeff’s rule
B.
Hofmann 's
C.
Markownikoff’s rule
D.
Kharasch effect
Correct Answer: A
Explanation:
Alkyl halide on heating with alcoholic KOH
undergoes dehydrohalogenation to yield alkene.
If in reaction, more than one alkene is formed,
then according to Saytzeff rule, the most highly
substituted alkene formed is the major product.
Assertion (A) $\mathrm{CH}_4$ does not react with $\mathrm{Cl}_2$ in dark.
Reason (R) Chlorination of $\mathrm{CH}_4$ takes place in sunlight.
A.
Both (A) and (R) are true and (R) is the correct explanation of (A).
B.
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
C.
(A) is true and (R) is false.
D.
Both (A) and (R) are false.
Correct Answer: A
Explanation:
Both assertion and reason are correct and
reason is the correct explanation of the assertion.
Chlorination of CH$_4$ does not take place in dark as this reaction follows free radical mechanism and free radicals are generated only in the presence of sunlight.
Greater the character of C-atom in hydrocarbons,
greater the electronegativity of that carbon and
thus greater the acidic nature of the H attached to
electronegative carbon.
With respect to the conformers of ethane, which of the following statements is true?
A.
Bond angle changes but bond length remains same.
B.
Both bond angle and bond length change.
C.
Both bond angle and bond length remain same.
D.
Bond angle remains same but bond length changes.
Correct Answer: C
Explanation:
Conformers are the isomers which are formed
by rotation about single bonds without any cleavage
of any bond. These conformers have same bond
angle between them and have same bond length
while their dihedral angle changes.
Pyrrole has maximum electron density on
2 and 5. It generally reacts with electrophiles at the
C-2 or C-5 due to the highest degree of stability of
the protonated intermediate.
Attack at position 3 or 4 yields a carbocation that is
a hybrid of structures (I) and (II). Attack at position
2 or 5 yields a carbocation that is a hybrid not only
of structures (III) and (IV) (analogous to I and II) but
also of structure (V). The extra stabilization conferred
by (V) makes this ion the more stable one.
Also, attack at position 2 or 5 is faster because the
developing positive charge is accommodated by
three atoms of the ring instead of by only two.
Which of the following can be used as the halide component for Friedel-Crafts reaction?
A.
Chlorobenzene
B.
Bromobenzene
C.
Chloroethene
D.
Isopropyl chloride
Correct Answer: D
Explanation:
Friedel–Crafts reaction :
Chlorobenzene, bromobenzene and chloroethene
are not suitable halide components as lone pair of
electrons of halogen are delocalized with $\pi $-bonds
to attain double bond (C = X) character.
In the reaction with HCl, an alkene reacts in accordance with the Markovnikov's rule to give a product 1-chloro-1 methylcyclohexane. The possible alkene is
What products are formed when the following compound is treated with Br2 in the presence of FeBr3?
A.
B.
C.
D.
Correct Answer: C
Explanation:
Methyl group is ortho para directing but due to steric hindrance effect, generated by two -CH3 groups substitution will not take place on position (I). Hence only two products are possible.
Among the following compounds the one that is most reactive towards electrophilic nitration is
A.
benzoic acid
B.
nitrobenzene
C.
toluene
D.
benzene
Correct Answer: C
Explanation:
Due to electron releasing group like —R,
—OH etc. increases the electron density at ortho
and para position and thus makes the benzene
ring more reactive towards electrophile. On the
other hand, electron withdrawing groups like —
COOH, —NO2 etc. reduces electron density and
thus reduces the reactivity of benzene towards
electrophile. Thus, the order is
Liquid hydrocarbons can be converted to a mixture of gaseous hydrocarbons by
A.
oxidation
B.
cracking
C.
distillation under reduced pressure
D.
hydrolysis
Correct Answer: B
Explanation:
On cracking or pyrolysis, the hydrocarbon with higher molecular mass gives a mixture of hydrocarbons having lower molecular masses. Hence, liquid hydrocarbons can be converted into a mixture of gaseous hydrocarbons. (Lower hydrocarbons exist in gaseous state while higher ones are in liquid state or solid state.)
Which of the following compounds will exhibit cis-trans (geometrical) isomerism?
A.
Butanol
B.
2-Butyne
C.
2-Butenol
D.
2-Butene
Correct Answer: D
Explanation:
Alkenes with double bonds cannot undergo free rotation and can have different geometrical shapes with two different groups on each end of the double bond.