LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc.

DEGREE EXAMINATION –CHEMISTRY

SECOND SEMESTER – APRIL 2007

CH 2502 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

Date & Time: 20/04/2007 / 1:00 – 4:00            Dept. No.                                                     Max. : 100 Marks

 

 

 

PART – A

 

Answer ALL the questions                                   (10 x 2 = 20)

 

1. Classify the following into +I and –I group: isopropyl, cyano, methoxy and
   t-butyl. Justify.
2. Write the structural formula for the following compounds
3. a) 1-hydroxy-2-propanone b) 3,5-octadiene
4. Arrange the following acids in the increasing order of the acid strength and justify your answer: (CH₃)₃C-COOH, H-COOH and CH₃-COOH.
5. Mention the differences between inductive effect and inductomeric effect.
6. Why is fluorination faster than chorination of alkane?
7. What is aromaticity? Explain with an example.
8. Why does maleic acid give anhydride readily and fumaric acid gives its anhydride only on heating?
9. Specify the E and Z notation to the following compounds:

 

 

 

9. What are the two alkyl halides formed on the addition of HCl to 3-methyl-1-butene?
10. What are polynuclear aromatic compounds? Give two examples.

 

PART – B

Answer any Eight questions                                                   (4 x 5 = 20)

11. Write various possible structural formulae of alkanes with molecular formula, C₆H₁₄ and write their IUPAC names.
12. Discuss the different factors affecting the stability of free radicals (primary, secondary and tertiary).
13. Explain Baeyer’s strain theory and theory of strainless ring.
14. Write short notes on i)Wurtz synthesis of hydrocarbons ii) Dieckmann’s synthesis of cycloalkanes.
15. What are the different conformers of cyclohexane? Give the structures and discuss which structure is more stable.
16. How is ethylene prepared in the laboratory? How does it react with i)bromine water ii) Con.H₂SO₄ iii) HCl iv) acidified KMnO₄ v) hypochlorous acid vi) ozone
17. Explain the mechanism of electrophilic substitution of (i) Friedal-Crafts  acylation (ii) sulphonation of benzene.
18. What is tautomerism? Explain keto-enol tautomerism in detail.
19. Why carboxyl group is meta orienting and carboxylate ion is ortho and para directing?
20. How will you prepare the following:

• n-propanol from propene (ii) Glycol from ethylene.

21. Explain the mechanism of markownikoff and antimarkownikoff addition of propene.
22. Write the structure of the product in the reaction of

 

Naphthalene                          H₂/Ni

Naphthalene               con.H₂SO₄/HgSO₄

2-pentyne                    Alkaline. KMnO₄

2-butyne                           O₃/hydrolysis

Naphthalene                         CH₂O+HCl

 

PART – C

 

Answer any FOUR questions                                            (4 x 10 = 40)

 

23. Explain the mode of hybridization of carbon in methane, ethylene and acetylene. Explain why aliphatic amines are more basic than aromatic amines.
24. Explain the mechanism of halogenation of alkanes and what are the factors affecting the rate of the reaction.
25. a) Why does the electrophilic substitution reaction of naphthalene take place in the carbon1(α) rather than on carbon 2 (β)
26. b) Explain the 1,4- and 1,2- addition reactions of dien in detail.
27. On reduction of compound C₆H₁₀(A) gives first C₆H₁₂(B) and finally C₆H₁₄(C). On ozonolysis followed by reduction (A) gives two aldehydes C₂H₄O (D) and C₂H₂O₂ (E). Oxidation of B with acidified potassium permanganate gives the acid C₃H₆O₂(F), Identify the compounds A to F and express the various reactions involved by means of equations.
28. a) What is orientation effect? Explain with examples.
29. b) Write short notes on i)Diels – Alder reaction ii) Hydroboration reaction.
30. Write the Newman projection formulae of comparatively stable conformation of butane. Which one of them is preferred conformation?

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 7

SECOND SEMESTER – APRIL 2008

CH 2502 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

 

Date : 23/04/2008                Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

 

PART – A

Answer ALL the questions                                                                            (10 x 2 = 20 marks)

 

1. Define homolytic cleavage with an example.
2. Explain why nitromethane is soluble and nitrobenzene is insoluble in NaOH.
3. How would you covert n-butane into isobutane?
4. Arrange the following alkanes in the increasing order of their boiling points

n– hexane, n-pentane, 2-methyl pentane.

1. Name the products obtained when 2-methyl -2- butene is subjected to ozonolysis.
2. Explain why is the chair form of cyclohexane more stable than the boat form.
3. Among ortho, meta and para-dichlorobenzenes, which isomer has the highest dipole moment?  Why?
4. Write down the combustion reaction of benzene.
5. Write the E, Z notation of the following compounds.

 

 

1. Mention any two differences between tautomerism and resonance.

 

                                                                        PART – B

Answer any EIGHT questions                                                                 (8 x 5 = 40 marks)

 

1. What are the requirements for a compound to be aromatic?
2. Discuss keto-enol tautomerism with an example.
3. Explain Dieckmann’s ring closure reaction.
4. Discuss Baeyer’s strain theory of ring compounds.
5. Discuss on the relative stability of dienes.
6. Explain the Saytzeff’s rule in elimination reactions.
7. How is acetylene prepared?  How does it react with   a) HCN   b) Excess of HBr

1. c) Acetic acid

1. Give the preparation, properties and uses of naphthalene.
2. Explain why – OH group is activating and o, p-directing where as -No₂ group is deactivating and m-directing.
3. Discuss the conformations of n-butane.
4. What are geometrical isomers?  How do the two isomers differ in their physical and chemical properties?
5. What are conformers?  How many conformers are possible for ethane?  Comment on their relative stabilities.

PART – C

Answer any FOUR questions                                                                  (4 x 10 = 40 marks)

 

1. a) Compare the basicities of 1^o, 2^o and 3^o amines with that of NH₃.  Give reason.           (6)

 

1. b) Arrange primary, secondary and tertiary carbocations in the increasing order of their

stabilities and explain.                                                                                                   (4)

 

1. a) How are alkanes prepared by Wurtz and House – Corey methods?                             (4)

 

1. b) How are the following conversions effected? (6)
   1. n-hexane into benzene
   2. methane into nitromethane

• propene into n-propyl bromide

1. Ethylene into ethylene glycol.

 

1. Write notes on the following:

1. Markownikoff’s rule
2. Allylic bromination by NBS

• Hydroboration

1. Diels – Alder reaction

 

1. a) How is benzene prepared and purified in the laboratory?                                             (6)

1. b) Starting form benzene how are the following compounds prepared?
2. i) Acetophenone
3. ii) 1,3,5-Trinitrobenzene                              (4)

 

1. Explain the following with examples

1. Addition polymerization        (3)
2. Zeigler – Natta polymerization        (4)

• Dehydrohalogenation        (3)

 

1. Discuss on the conformers of disubstituted cyclohexane and explain 1,2 and 1,3 interactions.

 

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       LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

WD 06

B.Sc. DEGREE EXAMINATION – CHEMISTRY

SECOND SEMESTER – April 2009

CH 2504 / 2502 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

 

Date & Time: 23/04/2009 / 1:00 – 4:00 Dept. No.                                                   Max. : 100 Marks

 

 

PART – A

Answer ALL the questions:                                                             (10 x 2 = 20)

 

1. Write the structural formula for the following compounds.
2. 3,3-Dimethyl-1-butene; b) But-2-en-1-ol.
3. Classify the following into +M and –M group

₂ ,   ₂ ,   ,

3. What happends when ethylchloride reacts with sodium metal.
4. What is aromaticity Explain with an example?
5. Specify the E and Z notation to the following compounds.
6. a) b)

 

6. What alkyl halide would yield each of the following pure alkene up on dehydro halogenation by a strong base. a) Isobutylene b) 3-methyl-l-butene.
7. In Fridel-craft’s alkylation of benzene using n-propyl chloride gave only Isopropyl benzene rather than n-propyl benzene. Explain.
8. Indicate which ring you would expect undergo nitration in phenylbenzoate.
9. Write the structure of (i) Cis-4-tert-butylmethyl cyclohexane.                           (ii) cis-1, 2-dimethyl cyclohexane
10. What are polynuclear aromatic compounds? Give two examples.

 

PART – B

Answer any EIGHT questions:                                                                   (8 x 5 = 40)

 

11. Write various possible structural formula of alkanes with molecular formula, C₅H₁₂ and write their IUPAC names.
12. Discuss the different factors affecting the stabilities of carbocation (1^o, 2^o and 3^o)
13. Explain Bayer’s strain theory.
14. How will you prepare cyclopentane using Dieckmann’s Synthesis.
15. What are different conformation of cyclohexane. Draw their structure and explain the stabilities.
16. How is ethylene prepared in the laboratroy? How does it react with
17. i) Bromine water ii) Conc. H₂SO₄ iii) HCl                                                            (2+3)
18. Explain the mechanism of Nitration of benzene.
19. What is tautomerism. Explain mitro-acinitro tautomerism exhibited by Nitroethane.
20. Explain by resonance structure that NO₂ is meta directing, where as –OH group is Ortho-para directing towards electrophillic aromatic substitution.
21. Explain the mechanism of Markownikoff’s Propene.

 

21. i) How will you differentiate 1-butyne from 2-butyne.
22. ii) Explain the mechanism of Hydroboration of propene.
23. Write the structure of the product for the following reaction.
24. Napthalene
25. Napthalene

• 2-butene

1. Nitrobenzene
2. Phenol

PART – C

Answer any FOUR questions:                                                                     (4 x 10 = 40)

 

23. a) Explain the type of hybridisation in the following
24. i) Benzene ii) 1, 3 – buta-diene iii) cyclohexane                       iv) l-butyne.
25. Which is more basic ethylamine or Aniline Explain.
26. a) Explain Hyper conjugation.
27. Arrange the compound in the increasing order of acid strength and Explain.
28. CCl₃ COOH ii) CH₃ COOH,           iii) CH₃ CH₂ CH₂ COOH       iv)CH₂Cl OOH
29. A hydrocarbon ‘A’ adds one mole of hydrogen in the presences of a platinum catalyst to form n-hexane. When A is oxidised vigourously with KMnO₄, a single carboxylic acid containing three carbon atoms is isolated. Give the structure and name of A. Show your reasoning including equation for all reactions.
30. i) Explain 1,2 – and 1,4 – addition of HBr with 1,3-butadiene.
31. Write the mechanism Fridel – Craft’s Acylation
32. i) Predict the product of Bromination of
33. Acetanilide b) cinnamic acid
34. Explain Diel’s Alder reaction taking suitable example.
35. Draw various possible conformation of n-butane explain their stabilities based on energy level diagram?

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

SECOND SEMESTER – APRIL 2011

CH 2504/CH 2502/CH 2500 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

 

Date : 08-04-2011              Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

PART – A

Answer ALL the questions.                                                                                        (10 x 2 = 20 marks)

 

1. Prove that naphthalene is aromatic using Huckel’s rule.
2. Draw the structure corresponding to the following IUPAC name.

     Hex-3-ene-5-yne.

3. What happens when ethyl chloride is treated with sodium metal?
4. How does cyclopropane react with HI.

     Write the product formed.

5. What is saytzeff’s rule?
6. Write the products obtained when propyne reacts with NaNH₂.
7. Complete the following reactions.

       

 

8. Explain why phenol is nitrated more readily than benzene.
9. Assign E or Z configuration to each of the following compounds.
10.           ii.

                            

 

10. What is meant by 1,3 diaxial interaction in methyl cyclohexane?

 

PART – B

Answer any EIGHT questions                                                                                       (8 x 5 = 40 marks)

 

11. Explain why benzyl carbonium ion is more stable than ethyl carbonium ion.
12. What is Hybridization?Explain why four covalent bonds in methane are equivalent.
13. Explain the free radical mechanism of chlorination of methane.
14. What is meant by Anti Markonikov addition. Give its mechanism.
15. What is hydroboration?Explain with an example.
16. How will you synthesize 1,3 butadiene from 1-butene.
17. Discuss the molecular orbital structure of benzene.
18. Although chlorine atom is an electron withdrawing group,it is ortho-para directing

     group.  Explain.

 

 

 

19. Explain Haworth’s synthesis of Naphthalene.
20. Define geometrical isomerism.Describe any one method of distinguishing between cis and

      trans isomers.

21. Discuss the relative stabilities of chair and boat conformations of cyclohexane.
22. Explain Baeyer’s strain theory?Why is it not applicable to cyclohexane.

 

PART – C

Answer any FOUR questions.                                                                                 (4 x 10 =40 marks)

 

23. a) Explain resonance with suitable examples.  (4)
24. b) Describe homolytic and heterolytic fission of a covalent bond.How carbonium ions,

          carbanions and free radicals are obtained.                                                                                 (6)

 

24. a) How will you synthesize cyclopentane using Dieckmann’s synthesis.       (4)
25. b) What is refining of petroleum?What different fractions are obtained on refining. (6)
26. Predict the products of the following reactions.   (10)                                                              

                 

             

 

26. a) Write a note on “stability of conjugated dienes”. (5)
27. b) Explain the mechanism of Nitration of benzene.       (5)
28. a) Explain Diel’s Alder reaction using suitable examples.       (4)
29. b) Predict the products of the following reactions.                                                                       (6)

 

       

 

28. Explain the various conformations of n-butane and discuss their stabilities based on the

      energy diagram.                                                                                                                                (10)

 

 

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

SECOND SEMESTER – APRIL 2012

CH 2504/CH 2502 – HYDROCARBONS AND STEREOCHEMISTRY

 

 

 

Date : 16-04-2012              Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

PART – A

 

ANSWER ALL THE QUESTIONS:                                                                      (10 x 2 = 20 marks)

 

1. Give the IUPAC name of CH₃-(CH₂) ₃-CH=CH-(CH₂) ₃-CH₃
2. What is hyper conjugation effect?
3. How will you prepare n-butane from ethyl chloride?
4. Draw the structures of isopentane and neopentane.
5. How does ethylene react with chlorine in water?
6. What happens when propene is treated with HBr?
7. Mention the electrophiles in the sulphonation and Friedel- Craft’s acylation reactions.
8. Name the products obtained when naphthalene is reduced in presence of Ni.
9. Draw any two conformational isomers for ethane and name them.
10. How does conformation differ from configuration?

 

PART – B

Answer any EIGHT Questions:                                                                            (8 x 5 = 40 marks)

 

11. What is meant by inductive effect? Explain the stabilities of 10, 20 and 30 carbocations using inductive effect.
12. Discus the type of hybridizations ethane, ethene and ethyne.
13. What is meant by a) aromatization and b) cracking.
14. Explain Dieckmann’s cyclization reaction.
15. What are the two alkenes obtained when neopentyl alcohol is dehydrated? Which of them is the major product and why?
16. What is peroxide effect? Explain why peroxide effect is observed in the addition of HBr only and not HCl & HI.
17. Explain ozonolysis reaction with an example.
18. Explain why OH group is activating and o, p-directing an aromatic electrophilic substitution reaction.
19. Discuss the mechanism of nitration of benzene.
20. Discuss the conformational analysis of n-butane.
21. What is geometrical isomerism? Discuss any two methods of differentiating geometric isomers.
22. Discuss the relative stabilities of chair and boad conformations of cyclohexane.

 

PART – C

Answer any FOUR Questions:                                                                            (4 x 10 = 40 marks)

 

23. a) Explain keto-enol tautomerism by taking acetoacetic ester as an example
24. b) Write the mechanism of keto-enol tautomerism. (5+5)
25. a) Expalin the mechanism of halogenations of alkanes.
26. b) Explain Baeyer’s strain theory. (5+5)
27. a) What is meant by allylic substitution? Give the mechanism of the reaction.
28. b) Comapre the acid strengths of ethane. Ethylene and acetylene. (5+5)
29. a) Explain Diels-Alder reaction and mention its synthetic applications.
30. b) Explain aromaticity of benzene using Huckel’s rule. (5+5)
31. a) Outline Haworth’s synthesis of naphthalene.
32. b) Name the products obtained when naphthalene is oxidized with
33. i) KMnO₄      ii) V₂O₅ iii) CrO₃                                                                                                             (5+5)
34. a) Explain why equatiorial conformation of methylcyclohexane is more stable than the

corresponding axial conformation.

1. b) What is 1,3-diaxial interaction? (7+3)

 

 

 

 

 

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