JEE Main - Alkanes conformations Sawhorse and Newman projections and halogenation Online Test (MCQ Quiz)

1. Which conformation of ethane is the most stable?

A) Eclipsed B) Staggered C) Skew D) Partially eclipsed

2. In the Newman projection of ethane, what is the dihedral angle between hydrogens on adjacent carbons in the eclipsed conformation?

A) 0 degrees B) 60 degrees C) 120 degrees D) 180 degrees

3. What is the dihedral angle between hydrogens on adjacent carbons in the staggered conformation of ethane?

A) 0 degrees B) 60 degrees C) 120 degrees D) 180 degrees

4. Which conformation of ethane has the highest potential energy?

A) Staggered B) Eclipsed C) Anti D) Gauche

5. The 'anti' conformation of butane is a type of which broader conformational class?

A) Eclipsed B) Staggered C) Skew D) Fully eclipsed

6. In the Newman projection of butane, which conformation has the two methyl groups positioned 180 degrees apart?

A) Syn-periplanar B) Anticlinic C) Synclinal D) Anticlinal

7. The 'gauche' conformation of butane is a type of which broader conformational class?

A) Eclipsed B) Staggered C) Fully eclipsed D) Syn-periplanar

8. What is the primary reason for the difference in stability between eclipsed and staggered conformations?

A) Hydrogen bonding B) Resonance stabilization C) Steric hindrance and torsional strain D) Aromaticity

9. In a Sawhorse projection, the bonds are viewed from which angle?

A) Head-on B) Side-on C) Top-down D) Bottom-up

10. Which projection method explicitly shows the dihedral angles between substituents on adjacent carbons?

A) Sawhorse projection B) Newman projection C) Fischer projection D) Kekulé structure

11. The eclipsed conformation where the largest groups are directly aligned is called:

A) Staggered B) Syn-periplanar C) Anti-periplanar D) Synclinal

12. The staggered conformation where the largest groups are 180 degrees apart is called:

A) Syn-periplanar B) Anti-periplanar C) Synclinal D) Anticlinic

13. The staggered conformation where the largest groups are 60 degrees apart is called:

A) Syn-periplanar B) Anti-periplanar C) Synclinal (Gauche) D) Anticlinic

14. Which of the following reactions is characteristic of alkanes?

A) Electrophilic addition B) Nucleophilic substitution C) Free radical substitution D) Electrophilic substitution

15. The halogenation of alkanes typically proceeds via which mechanism?

A) SN1 B) SN2 C) Free radical chain mechanism D) Addition-elimination

16. What is required to initiate the free radical halogenation of alkanes?

A) Strong acid catalyst B) Heat or UV light C) High pressure D) Oxidizing agent

17. Which step is the first step in the free radical halogenation of methane with chlorine?

A) Cl• + CH4 → HCl + •CH3 B) Cl2 + UV light → 2Cl• C) •CH3 + Cl2 → CH3Cl + Cl• D) •CH3 + Cl• → CH3Cl

18. Which step is the propagation step in the free radical halogenation of methane?

A) Cl2 + UV light → 2Cl• B) Cl• + CH4 → HCl + •CH3 C) •CH3 + Cl2 → CH3Cl + Cl• D) Cl• + Cl• → Cl2

19. Which step terminates the free radical chain reaction in alkane halogenation?

A) Cl2 + UV light → 2Cl• B) Cl• + CH4 → HCl + •CH3 C) •CH3 + Cl2 → CH3Cl + Cl• D) Combination of any two radicals

20. During the free radical chlorination of methane, what is the relative rate of substitution of hydrogen atoms in the order primary:secondary:tertiary?

A) 1:1:1 B) 1:3:5 C) 5:3:1 D) 1:5:3

21. Which halogen is most reactive in the free radical substitution of alkanes?

A) Fluorine B) Chlorine C) Bromine D) Iodine

22. Which halogen is least reactive and requires more forcing conditions for free radical substitution of alkanes?

A) Fluorine B) Chlorine C) Bromine D) Iodine

23. What is the primary product when propane is chlorinated under UV light?

A) 1-Chloropropane B) 2-Chloropropane C) 1,1-Dichloropropane D) 1,2-Dichloropropane

24. Why is the secondary hydrogen in propane more likely to be substituted than the primary hydrogen during free radical chlorination?

A) Secondary radical is more stable B) Primary radical is more stable C) Secondary radical is more reactive D) Primary radical is more reactive

25. The relative rate of attack on primary, secondary, and tertiary C-H bonds by chlorine radical is approximately:

A) 1:1:1 B) 1:4:5 C) 1:3.8:5.2 D) 5:3:1

26. The relative rate of attack on primary, secondary, and tertiary C-H bonds by bromine radical is approximately:

A) 1:1:1 B) 1:80:1600 C) 1:4:5 D) 5:3:1

27. Why is the selectivity of bromine radicals much higher than chlorine radicals in alkane halogenation?

A) Bromine radical is smaller B) Bromine radical is less reactive and more selective C) Bromine radical is more reactive and less selective D) Activation energy for bromine radical attack is lower

28. What is the main product of the free radical bromination of isobutane?

A) 1-Bromobutane B) 2-Bromobutane C) 2-Bromo-2-methylpropane D) 1-Bromo-2-methylpropane

29. The halogenation of alkanes with iodine is generally not synthetically useful because:

A) Iodine radical is too reactive B) The reaction is reversible and the reverse reaction is favored C) Iodine is too expensive D) No free radical is formed

30. What is the term for the energy difference between different conformations of a molecule?

A) Activation energy B) Reaction energy C) Conformational energy D) Bond energy

31. In the eclipsed conformation of ethane, the electron-electron repulsion between the bonding electrons of adjacent C-H bonds is known as:

A) Steric strain B) Torsional strain C) Angle strain D) Van der Waals strain

32. Which of the following is a synclinal conformation of butane?

A) Anti B) Gauche C) Syn-periplanar D) Fully eclipsed

33. The most stable conformation of cyclohexane is the:

A) Boat conformation B) Twist-boat conformation C) Chair conformation D) Half-chair conformation

34. In the chair conformation of cyclohexane, axial bonds are oriented:

A) Parallel to the ring plane B) Perpendicular to the ring plane C) At an angle to the ring plane D) Along the ring edge

35. In the chair conformation of cyclohexane, equatorial bonds are oriented:

A) Perpendicular to the ring plane B) Parallel to the ring plane C) Along the ring axis D) Vertically upwards

36. The interconversion of chair conformations of cyclohexane is called:

A) Rotation B) Inversion C) Ring flip D) Tautomerization

37. Which group experiences greater 1,3-diaxial strain in cyclohexane?

A) Equatorial methyl group B) Axial methyl group C) Axial hydrogen D) Equatorial hydrogen

38. What is the primary driving force for the formation of free radicals in halogenation?

A) Homolytic cleavage of a covalent bond B) Heterolytic cleavage of a covalent bond C) Nucleophilic attack D) Electrophilic attack

39. Which of the following is a termination step in the free radical chlorination of methane?

A) Cl2 + hv → 2Cl• B) Cl• + CH4 → HCl + •CH3 C) •CH3 + Cl2 → CH3Cl + Cl• D) 2Cl• → Cl2

40. The stability order of alkyl radicals is:

A) Primary > Secondary > Tertiary B) Tertiary > Secondary > Primary C) Secondary > Primary > Tertiary D) Primary > Tertiary > Secondary

41. The stability order of alkyl carbocations is the same as the stability order of:

A) Alkyl radicals B) Alkyl carbanions C) Alkenes D) Alkynes

42. In the free radical halogenation of a symmetrical alkane, how many distinct monohalogenated products are possible?

A) One B) Two C) Three D) Depends on the halogen

43. What is the main product when n-pentane is subjected to free radical chlorination?

A) 1-Chloropentane B) 2-Chloropentane C) 3-Chloropentane D) A mixture of isomers

44. Which conformation of cyclohexane has higher energy due to the steric repulsion between flagpole hydrogens?

A) Chair B) Boat C) Twist-boat D) Half-chair

45. The energy difference between the chair and boat conformations of cyclohexane is approximately:

A) 5-10 kcal/mol B) 10-15 kcal/mol C) 20-30 kcal/mol D) 50-60 kcal/mol

46. What is the term for the conformation where substituents on adjacent carbons are aligned in the same plane?

A) Staggered B) Eclipsed C) Skew D) Anti

47. Which of the following is NOT a type of strain in molecular conformations?

A) Torsional strain B) Steric strain C) Angle strain D) Aromatic strain

48. The free radical halogenation of alkanes is a method for:

A) Introducing unsaturation B) Functionalizing alkanes C) Breaking C-C bonds D) Cyclization

49. Which statement best describes the relative stability of butane conformations?

A) Anti > Gauche > Eclipsed B) Gauche > Anti > Eclipsed C) Eclipsed > Anti > Gauche D) Anti > Eclipsed > Gauche

Alkanes conformations Sawhorse and Newman projections and halogenation - Online Test

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