Chapter 12 Organic Chemistry: Some Basic Principles And Techniques

Question 1. Which of the following is the correct IUPAC name?

(i) 3-Ethyl-4, 4-dimethylheptane

(ii) 4,4-Dimethyl-3-ethylheptane

(iii) 5-Ethyl-4, 4-dimethylheptane

(iv) 4,4-Bis(methyl)-3-ethylheptane

Question 2. The IUPAC name for

(i) 1-hydroxypentane-1,4-dione

(ii) 1,4-dioxopentanol

(iii) 1-carboxybutan-3-one

(iv) 4-oxopentanoic acid

Question 3. The IUPAC name for

(i) 1-Chloro-2-nitro-4-methylbenzene

(ii) 1-Chloro-4-methyl-2-nitrobenzene

(iii) 2-Chloro-1-nitro-5-methylbenzene

(iv) m-Nitro-p-chlorotoluene

Question 4. Electronegativity of carbon atoms depends upon their state of hybridisation. In which of the following compounds, the carbon marked with asterisk is most electronegative?

(i) $CH_3 – CH_2 – *CH_2 –CH_3$

(ii) $CH_3 – *CH = CH – CH_3$

(iii) $CH_3 – CH_2 – C \equiv *CH$

(iv) $CH_3 – CH_2 – CH = *CH_2$

Question 5. In which of the following, functional group isomerism is not possible?

(i) Alcohols

(ii) Aldehydes

(iii) Alkyl halides

(iv) Cyanides

Question 6. The fragrance of flowers is due to the presence of some steam volatile organic compounds called essential oils. These are generally insoluble in water at room temperature but are miscible with water vapour in vapour phase. A suitable method for the extraction of these oils from the flowers is:

(i) Distillation

(ii) Crystallisation

(iii) Distillation under reduced pressure

(iv) Steam distillation

Question 7. During hearing of a court case, the judge suspected that some changes in the documents had been carried out. He asked the forensic department to check the ink used at two different places. According to you which technique can give the best results?

(i) Column chromatography

(ii) Solvent extraction

(iii) Distillation

(iv) Thin layer chromatography

Question 8. The principle involved in paper chromatography is

(i) Adsorption

(ii) Partition

(iii) Solubility

(iv) Volatility

Question 9. What is the correct order of decreasing stability of the following cations.

I.

II.

III.

(i) II > I > III

(ii) II > III > I

(iii) III > I > II

(iv) I > II > III

Question 10. Correct IUPAC name for

(i) 2- ethyl-3-methylpentane

(ii) 3,4- dimethylhexane

(iii) 2-sec-butylbutane

(iv) 2,3-dimethylbutane

Question 11. In which of the following compounds the carbon marked with asterisk is expected to have greatest positive charge?

(i) $*CH_3—CH_2—Cl$

(ii) $*CH_3—CH_2—Mg^+Cl^–$

(iii) $*CH_3—CH_2—Br$

(iv) $*CH_3—CH_2—CH_3$

Question 12. Ionic species are stabilised by the dispersal of charge. Which of the following carboxylate ion is the most stable?

(i)

(ii)

(iii)

(iv)

Question 13. Electrophilic addition reactions proceed in two steps. The first step involves the addition of an electrophile. Name the type of intermediate formed in the first step of the following addition reaction.

$H_3C—HC = CH_2 + H^+ \rightarrow ?$

(i) 2° Carbanion

(ii) 1° Carbocation

(iii) 2° Carbocation

(iv) 1° Carbanion

Question 14. Covalent bond can undergo fission in two different ways. The correct representation involving a heterolytic fission of $CH_3—Br$ is

(i)

(ii)

(iii)

(iv)

Question 15. The addition of HCl to an alkene proceeds in two steps. The first step is the attack of $H^+$ ion to C=C portion which can be shown as

(i)

(ii)

(iii)

(iv) All of these are possible

Question 16. Which of the following compounds contain all the carbon atoms in the same hybridisation state?

(i) $H—C \equiv C—C \equiv C—H$

(ii) $CH_3—C \equiv C—CH_3$

(iii) $CH_2 = C = CH_2$

(iv) $CH_2 = CH—CH = CH_2$

Question 17. In which of the following representations given below spatial arrangement of group/ atom different from that given in structure ‘A’?

(A)

(i)

(ii)

(iii)

(iv)

Question 18. Electrophiles are electron seeking species. Which of the following groups contain only electrophiles?

(i) $BF_3, NH_3, H_2O$

(ii) $AlCl_3, SO_3, NO_2^+$

(iii) $NO_2^+, CH_3^+, CH_3—C^+=O$

(iv) $C_2H_5^–, C_2H_5^+$

Question 19. Which of the following pairs are position isomers?

(i) I and II

(ii) II and III

(iii) II and IV

(iv) III and IV

Question 20. Which of the following pairs are not functional group isomers?

(i) II and III

(ii) II and IV

(iii) I and IV

(iv) I and II

Question 21. Nucleophile is a species that should have

(i) a pair of electrons to donate

(ii) positive charge

(iii) negative charge

(iv) electron deficient species

Question 22. Hyperconjugation involves delocalisation of ___________.

(i) electrons of carbon-hydrogen $\sigma$ bond of an alkyl group directly attached to an atom of unsaturated system.

(ii) electrons of carbon-hydrogen $\sigma$ bond of alkyl group directly attached to the positively charged carbon atom.

(iii) $\pi$-electrons of carbon-carbon bond

(iv) lone pair of electrons

Question 23. Which of the above compounds form pairs of metamers?

Question 24. Identify the pairs of compounds which are functional group isomers.

Question 25. Identify the pairs of compounds that represents position isomerism.

Question 26. Identify the pairs of compounds that represents chain isomerism.

Question 27. For testing halogens in an organic compound with $AgNO_3$ solution, sodium extract (Lassaigne’s test) is acidified with dilute $HNO_3$. What will happen if a student acidifies the extract with dilute $H_2SO_4$ in place of dilute $HNO_3$?

Question 28. What is the hybridisation of each carbon in $H_2C = C = CH_2$.

Question 29. Explain, how is the electronegativity of carbon atoms related to their state of hybridisation in an organic compound?

Question 30. Show the polarisation of carbon-magnesium bond in the following structure.

$CH_3—CH_2—CH_2—CH_2—Mg—X$

Question 31. Compounds with same molecular formula but differing in their structures are said to be structural isomers. What type of structural isomerism is shown by

$CH_3—S—CH_2—CH_2—CH_3$ and

Question 32. Which of the following selected chains is correct to name the given compound according to IUPAC system.

Question 33. In DNA and RNA, nitrogen atom is present in the ring system. Can Kjeldahl method be used for the estimation of nitrogen present in these? Give reasons.

Question 34. If a liquid compound decomposes at its boiling point, which method (s) can you choose for its purification. It is known that the compound is stable at low pressure, steam volatile and insoluble in water.

Question 35. Draw the possible resonance structures for

Question 36. Which of the following ions is more stable? Use resonance to explain your answer.

Question 37. The structure of triphenylmethyl cation is given below. This is very stable and some of its salts can be stored for months. Explain the cause of high stability of this cation.

Question 38. Write structures of various carbocations that can be obtained from 2-methylbutane. Arrange these carbocations in order of increasing stability.

Question 39. Three students, Manish, Ramesh and Rajni were determining the extra elements present in an organic compound given by their teacher. They prepared the Lassaigne’s extract (L.E.) independently by the fusion of the compound with sodium metal. Then they added solid $FeSO_4$ and dilute sulphuric acid to a part of Lassaigne’s extract. Manish and Rajni obtained prussian blue colour but Ramesh got red colour. Ramesh repeated the test with the same Lassaigne’s extract, but again got red colour only. They were surprised and went to their teacher and told him about their observation. Teacher asked them to think over the reason for this. Can you help them by giving the reason for this observation. Also, write the chemical equations to explain the formation of compounds of different colours.

Question 40. Name the compounds whose line formulae are given below :

(i)

(ii)

Question 41. Write structural formulae for compounds named as-

(a) 1-Bromoheptane

(b) 5-Bromoheptanoic acid

Question 42. Draw the resonance structures of the following compounds;

(i)

(ii) $CH_2 = CH—CH = CH_2$

(iii)

Question 43. Identify the most stable species in the following set of ions giving reasons :

(i) $\overset{+}{C}H_3, \quad \overset{+}{C}H_2Br, \quad \overset{+}{C}HBr_2, \quad \overset{+}{C}Br_3$

(ii) $CH_3\overset{+}{C}H_2, \quad CH_3CH_2\overset{+}{C}H_2$

Question 44. Give three points of differences between inductive effect and resonance effect.

Question 45. Which of the following compounds will not exist as resonance hybrid. Give reason for your answer :

(i) $CH_3OH$

(ii) $R—CONH_2$

(iii) $CH_3CH = CHCH_2NH_2$

Question 46. Why does $SO_3$ act as an electrophile?

Question 47. Resonance structures of propenal are given below. Which of these resonating structures is more stable? Give reason for your answer.

I: $\overset{+}{C}H_2-CH=CH-\overset{-}{O}$

II: $CH_2=CH-\overset{-}{C}H-\overset{+}{O}$

Question 48. By mistake, an alcohol (boiling point 97°C) was mixed with a hydrocarbon (boiling point 68°C). Suggest a suitable method to separate the two compounds. Explain the reason for your choice.

Question 49. Which of the two structures (A) and (B) given below is more stabilised by resonance? Explain.

$CH_3COOH$ and $CH_3COO^–$

(A) (B)

Question 50. Match the type of mixture of compounds in Column I with the technique of separation/purification given in Column II.

Column I

(i) Two solids which have different solubilities in a solvent and which do not undergo reaction when dissolved in it.

(ii) Liquid that decomposes at its boiling point

(iii) Steam volatile liquid

(iv) Two liquids which have boiling points close to each other

(v) Two liquids with large difference in boiling points.

Column II

(a) Steam distillation

(b) Fractional distillation

(c) Simple distillation

(d) Distillation under reduced pressure

(e) Crystallisation

Question 51. Match the terms mentioned in Column I with the terms in Column II.

Column I

(i) Carbocation

(ii) Nucleophile

(iii) Hyperconjugation

(iv) Isomers

(v) sp hybridisation

(vi) Electrophile

Column II

(a) Cyclohexane and 1- hexene

(b) Conjugation of electrons of C–H $\sigma$ bond with empty p-orbital present at adjacent positively charged carbon.

(c) $sp^2$ hybridised carbon with empty p-orbital

(d) Ethyne

(e) Species that can receive a pair of electrons

(f) Species that can supply a pair of electrons

Question 52. Match Column I with Column II.

Column I

(i) Dumas method

(ii) Kjeldahl’s method

(iii) Carius method

(iv) Chromatography

(v) Homolysis

Column II

(a) $AgNO_3$

(b) Silica gel

(c) Nitrogen gas

(d) Free radicals

(e) Ammonium sulphate

Question 53. Match the intermediates given in Column I with their probable structure in Column II.

Column I

(i) Free radical

(ii) Carbocation

(iii) Carbanion

Column II

(a) Trigonal planar

(b) Pyramidal

(c) Linear

Question 54. Match the ions given in Column I with their nature given in Column II.

Column I

(i)

(ii)

(iii)

(iv)

Column II

(a) Stable due to resonance

(b) Destabilised due to inductive effect

(c) Stabilised by hyperconjugation

(d) A secondary carbocation

Question 55. Assertion (A) : Simple distillation can help in separating a mixture of propan-1-ol (boiling point 97°C) and propanone (boiling point 56°C).

Reason (R) : Liquids with a difference of more than 20°C in their boiling points can be separated by simple distillation.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.

Question 56. Assertion (A) : Energy of resonance hybrid is equal to the average of energies of all canonical forms.

Reason (R) : Resonance hybrid cannot be presented by a single structure.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.

Question 57. Assertion (A) : Pent- 1- ene and pent- 2- ene are position isomers.

Reason (R) : Position isomers differ in the position of functional group or a substituent.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.

Question 58. Assertion (A) : All the carbon atoms in $H_2C = C = CH_2$ are $sp^2$ hybridised

Reason (R) : In this molecule all the carbon atoms are attached to each other by double bonds.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.

Question 59. Assertion (A) : Sulphur present in an organic compound can be estimated quantitatively by Carius method.

Reason (R) : Sulphur is separated easily from other atoms in the molecule and gets precipitated as light yellow solid.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.

Question 60. Assertion (A): Components of a mixture of red and blue inks can be separated by distributing the components between stationary and mobile phases in paper chromatography.

Reason (R) : The coloured components of inks migrate at different rates because paper selectively retains different components according to the difference in their partition between the two phases.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.

Question 61. What is meant by hybridisation? Compound $CH_2 = C = CH_2$ contains sp or $sp^2$ hybridised carbon atoms. Will it be a planar molecule?

Question 62. Benzoic acid is a organic compound. Its crude sample can be purified by crystallisation from hot water. What characteristic differences in the properties of benzoic acid and the impurity make this process of purification suitable?

Question 63. Two liquids (A) and (B) can be separated by the method of fractional distillation. The boiling point of liquid (A) is less than boiling point of liquid (B). Which of the liquids do you expect to come out first in the distillate? Explain.

Question 64. You have a mixture of three liquids A, B and C. There is a large difference in the boiling points of A and rest of the two liquids i.e., B and C. Boiling point of liquids B and C are quite close. Liquid A boils at a higher temperature than B and C and boiling point of B is lower than C. How will you separate the components of the mixture. Draw a diagram showing set up of the apparatus for the process.

Question 65. Draw a diagram of bubble plate type fractionating column. When do we require such type of a column for separating two liquids. Explain the principle involved in the separation of components of a mixture of liquids by using fractionating column. What industrial applications does this process have?

Question 66. A liquid with high boiling point decomposes on simple distillation but it can be steam distilled for its purification. Explain how is it possible?