Chem 112-internal 2005

UNIVERSAL SCIENCE COLLEGE (B.Sc. Biochemistry)

First Semester 2006 Second Term exam Subject: Organic Chemistry (Chem. 112) Date: - 02nd Jan. 2006

Full Marks: 100 Pass Marks: 45 Time: 3 Hours

Candidates are required to give their answers in their own words as far as practicable. The figure in the margin indicates full marks.

Group – A (Any Three)

(3 X 14=42)

1. Draw stereo-chemical formulas for all the possible stereo-isomers of the following compounds. Label pairs of enantiomers and meso compounds.Tell which isomers if separated from all other stereo-isomers ,will be optically active a) 1,2 –dibromopropane b)2,4 – dibromopentane c)2-bromo-3-chlorobutane d) 1, 3 –dichloro-2-methylbutane e)2,3,4- tribromohexane f) 1- chloro-2- methyl –butane g)1,2,3,4-tetrabromobutane

2. What is halogenation? Discuss the free radical chlorination of propane. 3. Explain, giving illustrations, the energetics of a reaction. 4. Discuss the mechanism, orientation and reactivity of the electrophilic addition and free radical addition of hydrogen bromide to alkene. (6 X 7=42) Group – B (Any Six) 1. 2. 3. 4. 5.

Describe methods for generation of carbenes and nitrenes. Explain various types of organic reactions giving examples. Account for the fact that cyclohexane is more stable among cycloalkanes. 4.Give an account of working of polarimeter. Write in short about the specific rotation The reaction of either 2-pentanol or 3—pentanol reacts with HCl to give both 2-chropentane and 3-cholopentane.Give reason with suitable mechanism. 6. Give five examples of nucleophilic and substitution reactions. 7. Give the mechanism for the following reactions. Hg(OAc)2,H2O a) (CH3)3- C-CH=CH2 ----------(CH3)3C- CHOH- CH3 (BH3)2

b) (CH3)3–C-CH=CH2 ----------8. Explain the structure of ethylene. Group –C (Any Eight) 1. 2. 3. 4. 5. 6. 7.

(CH3)3C- CH2CH2OH (8 X 2=16)

What is hybridization? What are reactive intermediates? Give the equation of relationship between free energy and equilibrium constant of reaction. Draw and specify as R or S enantiomer of 1,3 –dichloropentane CH3CH2CH2CHDCl (D=deuterium) What is Bayer strain theory? Mention the reasons for its draw backs. 8. Show your familiarity with axial and equatorial bonds in cyclohexane. 9. Give the product of this reaction with suitable mechanism 10. CH3CH2CH2Br + CH3OH -------? 11. Write about the industrial source of alkane. 12. What is dehydrohalogenation? 13. Name the alkene that gives acetaldehyde and acetone on ozonolysis .Show the process of ozonide formation for this reaction. 14. What is peroxide effect? 15. Give the mechanism of hydroboration.