1
MCQ (Single Correct Answer)

AIPMT 2002

Reactivity order of halides for dehydrologenation is
A
$$R - F > R - Cl > R - Br > R - {\rm I}$$
B
$$R - {\rm I} > R - Br > R - Cl > R - F$$
C
$$R - {\rm I} > R - Cl > R - Br > R - F$$
D
$$R - F > R - {\rm I} > R - Br > R - Cl$$

Explanation

atomic radii order :
I > Br > Cl > F

F, Cl, Br, I belongs to the same group orderly. Atomic radii go on increasing as the nuclear charge increases from top to bottom in a group. The decreasing order of bond length C – I > C – Br > C – Cl > C – F. The order of bond dissociation energy
R – F > R – Cl > R – Br > R – I. During dehydrohalogenation C – I bond breaks more easily than C – F bond.So reactivity order of halides

$$R - {\rm I} > R - Br > R - Cl > R - F$$
2
MCQ (Single Correct Answer)

AIPMT 2001


obtained by chlorination of n-butane will be
A
meso form
B
racemic mixture
C
d-form
D
$$l$$-form

Explanation

Chlorination of n-butane takes place via free radical formation.
3
MCQ (Single Correct Answer)

AIPMT 2001

An organic compound A(C4H9Cl) on reaction with Na/diethyl ether gives a hydrocarbon which on monochlorination gives only one chloro derivative then, A is
A
t-butyl chloride
B
s-butyl chloride
C
iso-butyl chloride
D
n-butyl chloride

Explanation

2C4H9Cl+2Na $$\buildrel {Ethanol} \over \longrightarrow $$ C4H9 - C4H9 + 2NaCl

In C4H9 - C4H9 i.e., (H3C)3C—C(CH3)3 there are primary hydrogens only.

Thus, only one chloro derivative is possible.
4
MCQ (Single Correct Answer)

AIPMT 2001

A compound of molecular formula C7H16 shows optical isomerism, compound will be
A
2, 3-dimethylpentane
B
2, 2-dimethylbutane
C
2-methylhexane
D
none of these

Explanation

Organic compounds exhibit the property of enantiomerism (optical isomerism) only when their molecules are chiral. Most chiral compounds have a chiral centre, which is an atom bonded to four different atoms or groups.
2,3-Dimethylpentane has one chiral C-atom and do not have any symmetric element.

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