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Chemistry · Textbook solutions

Organic Chemistry – Some Basic Principles and Techniques

Every solved example, exercise, and miscellaneous question — in the order the textbook teaches them. · 64 questions

Worked Examples

24 q

Solved Examples

Worked · 24
  1. Eg 8.1
    How many σ\sigma and π\pi bonds are present in each of the following molecules? (a) HC≡CCH=CHCH3\text{HC}\equiv\text{CCH}=\text{CHCH}_3 (b) CH2=C=CHCH3\text{CH}_2=\text{C}=\text{CHCH}_3
  2. Eg 8.2
    What is the type of hybridisation of each carbon in the following compounds? (a) CH3Cl\text{CH}_3\text{Cl} (b) (CH3)2CO(\text{CH}_3)_2\text{CO} (c) CH3CN\text{CH}_3\text{CN} (d) HCONH2\text{HCONH}_2 (e) CH3CH=CHCN\text{CH}_3\text{CH}=\text{CHCN}
  3. Eg 8.3
    Write the state of hybridisation of carbon in the following compounds and shapes of each of the molecules. (a) H2C=O\text{H}_2\text{C}=\text{O} (b) CH3F\text{CH}_3\text{F} (c) HC≡N\text{HC}\equiv\text{N}
  4. Eg 8.4
    Expand each of the following condensed formulas into their complete structural formulas. (a) CH3CH2COCH2CH3\text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3 (b) CH3CH=CH(CH2)3CH3\text{CH}_3\text{CH}=\text{CH}(\text{CH}_2)_3\text{CH}_3
  5. Eg 8.5
    For each of the following compounds, write a condensed formula and also their bond-line formula. (a) HOCH2CH2CH2CH(CH3)CH(CH3)CH3\text{HOCH}_2\text{CH}_2\text{CH}_2\text{CH}(\text{CH}_3)\text{CH}(\text{CH}_3)\text{CH}_3 (b) The structure in which a central CH\text{CH} carries an OH\text{OH} group above it and a −C≡N-\text{C}\equiv\text{N} group on each side: N≡C−CH(OH)−C≡N\text{N}\equiv\text{C}-\text{CH}(\text{OH})-\text{C}\equiv\text{N}
  6. Eg 8.6
    Expand each of the following bond-line formulas to show all the atoms including carbon and hydrogen. (a) A cyclohexane ring bearing a branched three-carbon group attached through its middle carbon (an isopropyl substituent). (b) An unbranched eight-vertex zig-zag chain. (c) A chain drawn as HC≡C−CH2−CH(OH)−CH3\text{HC}\equiv\text{C}-\text{CH}_2-\text{CH}(\text{OH})-\text{CH}_3 in bond-line form, the OH\text{OH} written below the fourth vertex. (d) Two CH\text{CH} vertices joined to each other, each carrying two methyl groups.
  7. Eg 8.7
    Structures and IUPAC names of some hydrocarbons are given below. Explain why the names given in the parentheses are incorrect. (a) CH3−CH(CH3)−CH2−CH2−CH(CH3)−CH(CH3)−CH2−CH3\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_2-\text{CH}(\text{CH}_3)-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 2,5,6-Trimethyloctane [and not 3,4,7-Trimethyloctane] (b) CH3−CH2−CH(CH2CH3)−CH2−CH(CH3)−CH2−CH3\text{CH}_3-\text{CH}_2-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 3-Ethyl-5-methylheptane [and not 5-Ethyl-3-methylheptane]
  8. Eg 8.8
    Write the IUPAC names of the compounds i–iv from their given structures. (i) CH3−CH2−CH(OH)−CH2−CH2−CH(CH3)−CH2−CH3\text{CH}_3-\text{CH}_2-\text{CH}(\text{OH})-\text{CH}_2-\text{CH}_2-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 (ii) CH3−CH2−CO−CH2−CO−CH3\text{CH}_3-\text{CH}_2-\text{CO}-\text{CH}_2-\text{CO}-\text{CH}_3 (iii) CH3−CO−CH2−CH2−CH2−COOH\text{CH}_3-\text{CO}-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{COOH} (iv) CH≡C−CH=CH−CH=CH2\text{CH}\equiv\text{C}-\text{CH}=\text{CH}-\text{CH}=\text{CH}_2
  9. Eg 8.9
    Derive the structure of (i) 2-Chlorohexane, (ii) Pent-4-en-2-ol, (iii) 3-Nitrocyclohexene, (iv) Cyclohex-2-en-1-ol, (v) 6-Hydroxyheptanal.
  10. Eg 8.10
    Write the structural formula of: (a) o-Ethylanisole (b) p-Nitroaniline (c) 2,3-Dibromo-1-phenylpentane (d) 4-Ethyl-1-fluoro-2-nitrobenzene
  11. Eg 8.11
    Using curved-arrow notation, show the formation of reactive intermediates when the following covalent bonds undergo heterolytic cleavage. (a) CH3−SCH3\text{CH}_3-\text{SCH}_3 (b) CH3−CN\text{CH}_3-\text{CN} (c) CH3−Cu\text{CH}_3-\text{Cu}
  12. Eg 8.12
    Giving justification, categorise the following molecules/ions as nucleophile or electrophile: HS−\text{HS}^{-}, BF3\text{BF}_3, C2H5O−\text{C}_2\text{H}_5\text{O}^{-}, (CH3)3N ⁣:(\text{CH}_3)_3\text{N}\!:, Cl+\overset{+}{\text{Cl}}, CH3−C+=O\text{CH}_3-\overset{+}{\text{C}}=\text{O}, H2N ⁣:−\text{H}_2\text{N}\!:^{-}, N+O2\overset{+}{\text{N}}\text{O}_2
  13. Eg 8.13
    Identify the electrophilic centre in the following: CH3CH=O\text{CH}_3\text{CH}=\text{O}, CH3CN\text{CH}_3\text{CN}, CH3I\text{CH}_3\text{I}.
  14. Eg 8.14
    Which bond is more polar in the following pairs of molecules: (a) H3C−H\text{H}_3\text{C}-\text{H}, H3C−Br\text{H}_3\text{C}-\text{Br} (b) H3C−NH2\text{H}_3\text{C}-\text{NH}_2, H3C−OH\text{H}_3\text{C}-\text{OH} (c) H3C−OH\text{H}_3\text{C}-\text{OH}, H3C−SH\text{H}_3\text{C}-\text{SH}
  15. Eg 8.15
    In which C−C\text{C}-\text{C} bond of CH3CH2CH2Br\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} is the inductive effect expected to be the least?
  16. Eg 8.16
    Write resonance structures of CH3COO−\text{CH}_3\text{COO}^{-} and show the movement of electrons by curved arrows.
  17. Eg 8.17
    Write resonance structures of CH2=CH−CHO\text{CH}_2=\text{CH}-\text{CHO}. Indicate relative stability of the contributing structures.
  18. Eg 8.18
    Explain why the following two structures, I and II, cannot be the major contributors to the real structure of CH3COOCH3\text{CH}_3\text{COOCH}_3. I: CH3−C+(−O−)−O¨−CH3\text{CH}_3-\overset{+}{\text{C}}(-\text{O}^{-})-\ddot{\text{O}}-\text{CH}_3 II: CH3−C(−O−)=O+−CH3\text{CH}_3-\text{C}(-\text{O}^{-})=\overset{+}{\text{O}}-\text{CH}_3
  19. Eg 8.19
    Explain why (CH3)3C+(\text{CH}_3)_3\overset{+}{\text{C}} is more stable than CH3C+H2\text{CH}_3\overset{+}{\text{C}}\text{H}_2, and C+H3\overset{+}{\text{C}}\text{H}_3 is the least stable cation.
  20. Eg 8.20
    On complete combustion, 0.246 g0.246\,\text{g} of an organic compound gave 0.198 g0.198\,\text{g} of carbon dioxide and 0.1014 g0.1014\,\text{g} of water. Determine the percentage composition of carbon and hydrogen in the compound.
  21. Eg 8.21
    In Dumas' method for estimation of nitrogen, 0.3 g0.3\,\text{g} of an organic compound gave 50 mL50\,\text{mL} of nitrogen collected at 300 K300\,\text{K} temperature and 715 mm715\,\text{mm} pressure. Calculate the percentage composition of nitrogen in the compound. (Aqueous tension at 300 K=15 mm300\,\text{K} = 15\,\text{mm})
  22. Eg 8.22
    During estimation of nitrogen present in an organic compound by Kjeldahl's method, the ammonia evolved from 0.5 g0.5\,\text{g} of the compound in Kjeldahl's estimation of nitrogen neutralized 10 mL10\,\text{mL} of 1 M1\,\text{M} H2SO4\text{H}_2\text{SO}_4. Find out the percentage of nitrogen in the compound.
  23. Eg 8.23
    In Carius method of estimation of halogen, 0.15 g0.15\,\text{g} of an organic compound gave 0.12 g0.12\,\text{g} of AgBr\text{AgBr}. Find out the percentage of bromine in the compound.
  24. Eg 8.24
    In sulphur estimation, 0.157 g0.157\,\text{g} of an organic compound gave 0.4813 g0.4813\,\text{g} of barium sulphate. What is the percentage of sulphur in the compound?

Exercises

40 q
  1. Ex 8.1
    What are hybridisation states of each carbon atom in the following compounds ? CH2=C=O\text{CH}_2=\text{C}=\text{O}, CH3CH=CH2\text{CH}_3\text{CH}=\text{CH}_2, (CH3)2CO(\text{CH}_3)_2\text{CO}, CH2=CHCN\text{CH}_2=\text{CHCN}, C6H6\text{C}_6\text{H}_6
  2. Ex 8.2
    Indicate the σ\sigma and π\pi bonds in the following molecules : C6H6\text{C}_6\text{H}_6, C6H12\text{C}_6\text{H}_{12}, CH2Cl2\text{CH}_2\text{Cl}_2, CH2=C=CH2\text{CH}_2=\text{C}=\text{CH}_2, CH3NO2\text{CH}_3\text{NO}_2, HCONHCH3\text{HCONHCH}_3
  3. Ex 8.3
    Write bond line formulas for : Isopropyl alcohol, 2,3-Dimethylbutanal, Heptan-4-one.
  4. Ex 8.4
    Give the IUPAC names of the following compounds : (a) CH3CH2CH2−C6H5\text{CH}_3\text{CH}_2\text{CH}_2-\text{C}_6\text{H}_5 (b) CH3CH2CH(CH3)CH2CN\text{CH}_3\text{CH}_2\text{CH}(\text{CH}_3)\text{CH}_2\text{CN} (c) CH3CH(CH3)CH2CH2CH(CH3)CH2CH3\text{CH}_3\text{CH}(\text{CH}_3)\text{CH}_2\text{CH}_2\text{CH}(\text{CH}_3)\text{CH}_2\text{CH}_3 (d) CH3CH2C(Cl)(Br)CH2CH2CH2CH3\text{CH}_3\text{CH}_2\text{C}(\text{Cl})(\text{Br})\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3 (e) ClCH2CH2CHO\text{ClCH}_2\text{CH}_2\text{CHO} (f) Cl2CHCH2OH\text{Cl}_2\text{CHCH}_2\text{OH}
  5. Ex 8.5
    Which of the following represents the correct IUPAC name for the compounds concerned ? (a) 2,2-Dimethylpentane or 2-Dimethylpentane (b) 2,4,7-Trimethyloctane or 2,5,7-Trimethyloctane (c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane (d) But-3-yn-1-ol or But-4-ol-1-yne.
  6. Ex 8.6
    Draw formulas for the first five members of each homologous series beginning with the following compounds. (a) H−COOH\text{H}-\text{COOH} (b) CH3COCH3\text{CH}_3\text{COCH}_3 (c) H−CH=CH2\text{H}-\text{CH}=\text{CH}_2
  7. Ex 8.7
    Give condensed and bond line structural formulas and identify the functional group(s) present, if any, for : (a) 2,2,4-Trimethylpentane (b) 2-Hydroxy-1,2,3-propanetricarboxylic acid (c) Hexanedial
  8. Ex 8.8
    Identify the functional groups in the following compounds (a) A benzene ring carrying −CHO-\text{CHO} at C-1, −OMe-\text{OMe} (i.e. −OCH3-\text{OCH}_3) at C-3 and −OH-\text{OH} at C-4. (b) A benzene ring carrying −NH2-\text{NH}_2 at C-4 and −C(=O)−OCH2CH2N(C2H5)2-\text{C}(=\text{O})-\text{OCH}_2\text{CH}_2\text{N}(\text{C}_2\text{H}_5)_2 at C-1. (c) A benzene ring carrying −CH=CHNO2-\text{CH}=\text{CHNO}_2.
  9. Ex 8.9
    Which of the two: O2NCH2CH2O−\text{O}_2\text{NCH}_2\text{CH}_2\text{O}^{-} or CH3CH2O−\text{CH}_3\text{CH}_2\text{O}^{-} is expected to be more stable and why?
  10. Ex 8.10
    Explain why alkyl groups act as electron donors when attached to a π\pi system.
  11. Ex 8.11
    Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. (a) C6H5OH\text{C}_6\text{H}_5\text{OH} (b) C6H5NO2\text{C}_6\text{H}_5\text{NO}_2 (c) CH3CH=CHCHO\text{CH}_3\text{CH}=\text{CHCHO} (d) C6H5−CHO\text{C}_6\text{H}_5-\text{CHO} (e) C6H5−C+H2\text{C}_6\text{H}_5-\overset{+}{\text{C}}\text{H}_2 (f) CH3CH=CH C+H2\text{CH}_3\text{CH}=\text{CH}\,\overset{+}{\text{C}}\text{H}_2
  12. Ex 8.12
    What are electrophiles and nucleophiles ? Explain with examples.
  13. Ex 8.13
    Identify the reagents shown in bold in the following equations as nucleophiles or electrophiles: (a) CH3COOH+HO−→CH3COO−+H2O\text{CH}_3\text{COOH} + \mathbf{\text{HO}^{-}} \rightarrow \text{CH}_3\text{COO}^{-} + \text{H}_2\text{O} (b) CH3COCH3+−CN→(CH3)2C(CN)(OH)\text{CH}_3\text{COCH}_3 + \mathbf{{}^{-}\text{CN}} \rightarrow (\text{CH}_3)_2\text{C}(\text{CN})(\text{OH}) (c) C6H6+CH3C+O→C6H5COCH3\text{C}_6\text{H}_6 + \mathbf{\text{CH}_3\overset{+}{\text{C}}\text{O}} \rightarrow \text{C}_6\text{H}_5\text{COCH}_3
  14. Ex 8.14
    Classify the following reactions in one of the reaction type studied in this unit. (a) CH3CH2Br+HS−→CH3CH2SH+Br−\text{CH}_3\text{CH}_2\text{Br} + \text{HS}^{-} \rightarrow \text{CH}_3\text{CH}_2\text{SH} + \text{Br}^{-} (b) (CH3)2C=CH2+HCl→(CH3)2ClC−CH3(\text{CH}_3)_2\text{C}=\text{CH}_2 + \text{HCl} \rightarrow (\text{CH}_3)_2\text{ClC}-\text{CH}_3 (c) CH3CH2Br+HO−→CH2=CH2+H2O+Br−\text{CH}_3\text{CH}_2\text{Br} + \text{HO}^{-} \rightarrow \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O} + \text{Br}^{-} (d) (CH3)3C−CH2OH+HBr→(CH3)2CBrCH2CH2CH3+H2O(\text{CH}_3)_3\text{C}-\text{CH}_2\text{OH} + \text{HBr} \rightarrow (\text{CH}_3)_2\text{CBrCH}_2\text{CH}_2\text{CH}_3 + \text{H}_2\text{O}
  15. Ex 8.15
    What is the relationship between the members of following pairs of structures ? Are they structural or geometrical isomers or resonance contributors ? (a) CH3CH2−CO−CH2CH3\text{CH}_3\text{CH}_2-\text{CO}-\text{CH}_2\text{CH}_3 and CH3CH2CH2−CO−CH3\text{CH}_3\text{CH}_2\text{CH}_2-\text{CO}-\text{CH}_3 (b) A C=C\text{C}=\text{C} in which the left carbon carries D\text{D} above and H\text{H} below while the right carbon carries H\text{H} above and D\text{D} below; and a C=C\text{C}=\text{C} in which the left carbon carries D\text{D} above and H\text{H} below while the right carbon carries D\text{D} above and H\text{H} below. (c) H−C(=O+H)−OH\text{H}-\text{C}(=\overset{+}{\text{O}}\text{H})-\text{OH} and H−C+(OH)−OH\text{H}-\overset{+}{\text{C}}(\text{OH})-\text{OH}
  16. Ex 8.16
    For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion. (a) CH3O−OCH3→CH3O˙+O˙CH3\text{CH}_3\text{O}-\text{OCH}_3 \rightarrow \text{CH}_3\dot{\text{O}} + \dot{\text{O}}\text{CH}_3 (b) (CH3)2C=O+−OH→−CH2C(CH3)=O+H2O(\text{CH}_3)_2\text{C}=\text{O} + {}^{-}\text{OH} \rightarrow {}^{-}\text{CH}_2\text{C}(\text{CH}_3)=\text{O} + \text{H}_2\text{O} (c) (CH3)3C−Br→(CH3)3C++Br−(\text{CH}_3)_3\text{C}-\text{Br} \rightarrow (\text{CH}_3)_3\overset{+}{\text{C}} + \text{Br}^{-} (d) C6H6+E+→\text{C}_6\text{H}_6 + \text{E}^{+} \rightarrow the cyclohexadienyl cation in which one ring carbon bears E\text{E} and the ring carries a positive charge
  17. Ex 8.17
    Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids? (a) Cl3CCOOH>Cl2CHCOOH>ClCH2COOH\text{Cl}_3\text{CCOOH} > \text{Cl}_2\text{CHCOOH} > \text{ClCH}_2\text{COOH} (b) CH3CH2COOH>(CH3)2CHCOOH>(CH3)3C.COOH\text{CH}_3\text{CH}_2\text{COOH} > (\text{CH}_3)_2\text{CHCOOH} > (\text{CH}_3)_3\text{C.COOH}
  18. Ex 8.18
    Give a brief description of the principles of the following techniques taking an example in each case. (a) Crystallisation (b) Distillation (c) Chromatography
  19. Ex 8.19
    Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.
  20. Ex 8.20
    What is the difference between distillation, distillation under reduced pressure and steam distillation ?
  21. Ex 8.21
    Discuss the chemistry of Lassaigne's test.
  22. Ex 8.22
    Differentiate between the principle of estimation of nitrogen in an organic compound by (i) Dumas method and (ii) Kjeldahl's method.
  23. Ex 8.23
    Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
  24. Ex 8.24
    Explain the principle of paper chromatography.
  25. Ex 8.25
    Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
  26. Ex 8.26
    Explain the reason for the fusion of an organic compound with metallic sodium for testing nitrogen, sulphur and halogens.
  27. Ex 8.27
    Name a suitable technique of separation of the components from a mixture of calcium sulphate and camphor.
  28. Ex 8.28
    Explain, why an organic liquid vaporises at a temperature below its boiling point in its steam distillation ?
  29. Ex 8.29
    Will CCl4\text{CCl}_4 give white precipitate of AgCl\text{AgCl} on heating it with silver nitrate? Give reason for your answer.
  30. Ex 8.30
    Why is a solution of potassium hydroxide used to absorb carbon dioxide evolved during the estimation of carbon present in an organic compound?
  31. Ex 8.31
    Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?
  32. Ex 8.32
    An organic compound contains 69% carbon and 4.8% hydrogen, the remainder being oxygen. Calculate the masses of carbon dioxide and water produced when 0.20 g0.20\,\text{g} of this substance is subjected to complete combustion.
  33. Ex 8.33
    A sample of 0.50 g0.50\,\text{g} of an organic compound was treated according to Kjeldahl's method. The ammonia evolved was absorbed in 50 ml50\,\text{ml} of 0.5 M0.5\,\text{M} H2SO4\text{H}_2\text{SO}_4. The residual acid required 60 mL60\,\text{mL} of 0.5 M0.5\,\text{M} solution of NaOH\text{NaOH} for neutralisation. Find the percentage composition of nitrogen in the compound.
  34. Ex 8.34
    0.3780 g0.3780\,\text{g} of an organic chloro compound gave 0.5740 g0.5740\,\text{g} of silver chloride in Carius estimation. Calculate the percentage of chlorine present in the compound.
  35. Ex 8.35
    In the estimation of sulphur by Carius method, 0.468 g0.468\,\text{g} of an organic sulphur compound afforded 0.668 g0.668\,\text{g} of barium sulphate. Find out the percentage of sulphur in the given compound.
  36. Ex 8.36
    In the organic compound CH2=CH−CH2−CH2−C≡CH\text{CH}_2=\text{CH}-\text{CH}_2-\text{CH}_2-\text{C}\equiv\text{CH}, the pair of hydridised orbitals involved in the formation of: C2−C3\text{C}_2-\text{C}_3 bond is:
    1. A.
      sp−sp2sp - sp^2
    2. B.
      sp−sp3sp - sp^3
    3. C.
      sp2−sp3sp^2 - sp^3
    4. D.
      sp3−sp3sp^3 - sp^3
  37. Ex 8.37
    In the Lassaigne's test for nitrogen in an organic compound, the Prussian blue colour is obtained due to the formation of:
    1. A.
      Na4[Fe(CN)6]\text{Na}_4[\text{Fe}(\text{CN})_6]
    2. B.
      Fe4[Fe(CN)6]3\text{Fe}_4[\text{Fe}(\text{CN})_6]_3
    3. C.
      Fe2[Fe(CN)6]\text{Fe}_2[\text{Fe}(\text{CN})_6]
    4. D.
      Fe3[Fe(CN)6]4\text{Fe}_3[\text{Fe}(\text{CN})_6]_4
  38. Ex 8.38
    Which of the following carbocation is most stable ?
    1. A.
      (CH3)3C. C+H2(\text{CH}_3)_3\text{C}.\,\overset{+}{\text{C}}\text{H}_2
    2. B.
      (CH3)3C+(\text{CH}_3)_3\overset{+}{\text{C}}
    3. C.
      CH3CH2C+H2\text{CH}_3\text{CH}_2\overset{+}{\text{C}}\text{H}_2
    4. D.
      CH3C+H CH2CH3\text{CH}_3\overset{+}{\text{C}}\text{H}\,\text{CH}_2\text{CH}_3
  39. Ex 8.39
    The best and latest technique for isolation, purification and separation of organic compounds is:
    1. A.
      Crystallisation
    2. B.
      Distillation
    3. C.
      Sublimation
    4. D.
      Chromatography
  40. Ex 8.40
    The reaction: CH3CH2I+KOH(aq)→CH3CH2OH+KI\text{CH}_3\text{CH}_2\text{I} + \text{KOH}(\text{aq}) \rightarrow \text{CH}_3\text{CH}_2\text{OH} + \text{KI} is classified as :
    1. A.
      electrophilic substitution
    2. B.
      nucleophilic substitution
    3. C.
      elimination
    4. D.
      addition