LOYOLA COLLEGE (AUTONOMOUS), CHENNAI600 034.
B.Sc. DEGREE EXAMINATION  CHEMISTRY
SECOND SEMESTER  APRIL 2003
CH 2500/ CHE 502 ORGANIC CHEMISTRY  I
23.04.2002
9.00  12.00
Max: 100 Marks
PART  A
Answer ALL the questions.
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(10  2 = 20 Marks)
Which alcohol of the following pair would you expect to be more
easily dehydrated? Why?
(CH3) C(OH) CH2 CH3 (or) (CH3)2 CH CH (OH) CH3.
State and explain Markonikov’s rule.
How would you distinguish 1butyne from 2butyne?
Identify the product in the following.
RCH = CH2 + CCl4 Peroxide
?
AntiMarkonikov’s rule is possible only for the addition of HBr in presence of
peroxides to an unsymmetrical alkene and not for HCl or HI. Why?
‘The presence of a small amount of O2 slows down the chlorination of
methane’. Explain.
In a study of Chlorination of propane, four products of formula C3 H6 Cl2
were isolated. What are their structures?
Acidity of the following Carboxylic acids is in the following order.
Cl2 CH COOH  F CH2 COOH  Cl CH2 COOH. Explain.
Many but not all molecules  that contain a cheral centre are chiral. Explain.
How do the properties of diasteromers compare?
PART  B
(8  5 = 40 Marks)
Answer any eight questions
Identify the products of obtained in the dehydration of 3 methy1-2 butanol.
Which one is major? Justify your answer.
Arrange the following compounds in order of reactivity toward
dehydrohalogenation by strong base. Account for your answer.
1bromobutone, 1brome2,2  dimethyl propane,
1bromo2 methylbutane, 1bromo3methylbutane.
Account for the following
(i)
trans alkene is more stable than cis alkene.
(ii)
NBS is preferred for allylic halogenation.
98% H2 SO4 is required to hydrate ethylene while 63% H2 SO4 is enough for
isobutylene. Explain
Explain with mechanism the addition of HBr to 1,3butadiene as 1,2 Vs 1,4
addition.
How would you prepare cis and trans alkenes from alkynes?
Explain with an example.
Give the mechanism of chlorination of methane is the presence of uv light.
Explain the relative reactivities of F2, Cl2, Br2 & I2 towards methane.
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How do you prepare the following?
(i)
nnonane starting with CH3 Br.
(ii)
3 methyl octane starting with secbutyl chloride.
In the halogenation of alkanes, bromine atom is much more selective than
chlorine atom. Explain [ relative rate factors of 1600: 82:1 for Br2 Vs 5.0:
3.8:1 for Cl2 for the reaction at tertiary: secondary: primary hydrogen]
Account for the following.
(a)
Chlorination of ethane is 400 times faster than that of methane when
equimolar amounts of both are reacted with a small amount of C12 .
(b)
chlorination of propane gives 45% of CH3 CH2 CH2 Cl and
55% of CH3CH(Cl) CH3.
Draw and specify as R or S, the enantiomers of
(i) CH3 CH (OH) COOH (ii) Secbutyl chloride
(iii) Bromo chloro iodomethane
What is a racemic modification? Discuss any two methods of resolving a
recemic modification.
PART  C
(4  10 = 40 Marks)
Answer any FOUR questions.
a) Explain the stability of conjugated dienes based on hydrogenation data.
b) Explain the acidity of acetylene compared with water, ammonia and
alkanes.
Account for the following
a)
Hydration of acetylene gives CH3CHO.
b)
Industrially acetylene is prepared from coal.
c)
Propene reacts with HOCl gives propylene chloro hydrin.
d)
2methyllbutanol on dehydration mainly gives 2methyl 2butene.
e)
Secbutyl trimethyl ammonium ion on treatment with strong base
undergoes elimination.
a) Explain the mechanism of addition of halogens to alkene.
b) Explain the mechanism of antiMarkonikov’s rule.
Explain homogenous and heterogeneous hydrogenation of alkenes with an
example. Discuss the mechanism for both in detail.
Draw the different conformation of ethane and nbutane, considering the
rotations about the bonds shown. CH3CH3 and CH3CH2CH2CH3. Draw the
potential energy Vs rotation curve for both and explain the strain and
rotational barrier involved.
Draw the stereocherical formulas of the dichlorobutanes obtained by the
freeradical chlorination of (i) (S) Secbatyl chloride, (ii) (R) Secbutyl
chloride and (iii) racemicSecbutyl chloride. Give the ratios of the
different 2,3dichlorobutanes obtained in the case of (i),(ii) & (iii) and
Explain. Also comment on the optical activity of the mixtures of
2,3dichlorobutanes obtained in (i) ,(ii), & (iii).
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