1000 Multiple-Choice Questions in Organic Chemistry   Multiple choice questions usually include a phrase or stem followed by three to five options/choices. Test strategies : • Read the directions carefully • Know if you are penalized for guessing • Answer easy questions first Answering options : • Improve your odds, think critically • Hide the options, read the stem, and try to answer Select the option that most closely matches your answer • Read the stem with each option Treat each option as a true-false question, and choose the “most true” Strategies to answer difficult questions : • Eliminate options you know to be incorrect • Question options that are totally unfamiliar to you • Question options that contain negative or absolute words • “All of the above” If you know two of the three options seem correct, “all of the above” is a strong possibility • Number answers : Toss out the high and low and consider the middle range numbers • “Look alike options” Probably one is correct; choose the best but eliminate choices that mean basically the same thing, and thus cancel each other out • Echo options : If two options are opposite each other , chances are one of them is correct • If two alternatives seem correct, compare them for differences, then refer to the stem to find your best answer Guessing : • Always guess when there is no penalty for guessing or you can eliminate options • Don’t guess if you are penalized for guessing and if you have no basis for your choice • Don’t change your answer unless you are sure of the correction When taking a test you are demonstrating your ability to understand your course material. Successful test taking avoids carelessness. Stay relaxed and confident. Remind yourself that you are well-prepared and going to do well. If you find yourself anxious, take several slow, deep breaths to relax. Don’t talk about the tests to other students just before it; anxiety is contagious. This unit includes 1000 multiple choice questions. The purpose is to assess the breadth of student’s knowledge and understanding of the basic concepts of organic chemistry. Remember that the multiple choice questions : 1. are not simply definitions. 2. require application of recalled information, not simple recall. 3. require fine distinctions between correct and nearly- correct statements. 4. emphasize conceptual understanding   These questions have been especially designed to cover all the important concepts of organic chemistry. Solve them carefully. You will be glad that you did ! 1. Which of the following is not a characteristic of organic compounds? (a) They usually have low melting points. (b) They usually are only slightly soluble or insoluble in water. (c) If water soluble they seldom conduct an electric current. (d) Bonds which bind the atoms together are nearly always ionic. Answer. (d) 2. The element least likely to be found in an organic compound is (a) oxygen (b) sulfur (c) nitrogen (d) silicon Answer. (d) 3. One of the major sources of organic compounds is (a) Natural gas (b) Fermentation (c) Sea water (d) Atmosphere Answer. (a) 4. Catenation is a property of the carbon atom which describes its ability to (a) bond with other carbon atoms (b) form double and triple bonds (c) exist in plant and animal form (d) form bonds in its ground state Answer. (a) 5. In stable organic compounds, carbon will always form (a) 2 bonds (b) 4 bonds (c) 3 bonds (d) 5 bonds Answer. (b) 6. Carbon-carbon double bonds consist of : (a) one σ bond, one π bond (b) two σ bonds, one π bond (c) one σ bond, two π bonds (d) two σ bonds, two π bonds Answer. (a) 7. Acetylene has a total of : (a) one σ bond, two π bonds (b) two σ bonds, four π bonds (c) three σ bonds, two π bonds (d) one σ bond, four π bonds Answer. (c) 8. In propene there are (a) eight σ bonds and one π bond (b) seven σ bonds and two π bonds (c) six σ bonds and three π bonds (d) nine σ bonds Answer. (a) 9. In propyne there are (a) six σ bonds and two π bonds (b) seven σ bonds and one π bond (c) six σ bonds and one π bond (d) eight σ bonds Answer. (a) 10. 1-Buten-3-yne has (a) six σ and four π bonds (b) seven σ and three π bonds (c) eight σ and two π bonds (d) nine σ and one π bond Answer. (b) 11. Compound in which carbons use only sp3 hybrid orbitals for bond formation is (a) CH CH CH 3 2 3 (b) CH C≡CH 3 (c) CH CH=CH 3 2 (d) CH =CH—CH=CH 2 2 Answer. (a) 12. Compound in which carbon uses sp3 hybrid orbitals for bond formation is (a) (b) (c) (d) (CH ) COH 3 3 Answer. (d) 13. When the carbon atom is sp2 hybridized in a compound, it is bonded to (a) 2 other atoms (b) 4 other atoms (c) 3 other atoms (d) 5 other atoms Answer. (c) 14. Compound in which carbons use only sp2 hybrid orbitals for bond formation is (a) (b) (c) CH =CH–CH=CH 2 2 (d) CH CH=C=CH 3 2 Answer. (c) 15. Which of the following is a planar molecule? (a) Formaldehyde (b) Acetone (c) Formic acid (d) Acetic acid Answer. (a) 16. What is bond angle between the hybrid orbitals in methane? (a) 180° (b) 120° (c) 109.5° (d) 115.5° Answer. (c) 17. The H–C–C bond angle in ethane is (a) 60° (b) 109.5° (c) 120° (d) 118°28′ Answer. (b) 18. The H–C–H bond angle in ethylene is (a) 60° (b) 120° (c) 90° (d) 180° Answer. (b) 19. What is the bond length of a carbon-carbon double bond? (a) 1.20 Å (b) 1.34 Å (c) 1.54 Å (d) 1.68 Å Answer. (b) 20. The carbon-carbon bond lengths in rank of increasing bond length is : (a) triple, double, single (b) single, double, triple (c) single, triple, double (d) triple, single, double Answer. (a) 21. Which of the following is the correct order of bond lengths : (a) C–C < C=C < C≡C (b) C–C > C≡C > C=C (c) C≡C > C–C > C=C (d) C≡C < C–C > C=C Answer. (a) 22. Which of the following hydrocarbons has the shortest C– C bond length? (a) CH =CH 2 2 (b) CH CH 3 3 (c) HC≡CH (d) Answer. (c) 23. The carbon-carbon bond length is maximum in (a) CH =CH 2 2 (b) CH CH 3 3 (c) HC≡CH (d) Answer. (b) 24. What is the hybridization of the carbon atoms numbered 1 and 2 respectively in the following structure? (a) sp3, sp2 (b) sp2, sp2 (c) sp, sp (d) sp2, sp Answer. (d) 25. How many atoms are attached to an atom having a sp hybridization? (a) 0 (b) 1 (c) 2 (d) 3 Answer. (c) 26. Which statement is true? (a) Resonance hybrids are inherently unstable. (b) Resonance hybrids are more stable than any individual resonance form. (c) Resonance hybrids are averages of all resonance forms resembling the less stable forms. (d) Resonance hybrids are averages of all resonance forms resembling the more stable forms. Answer. (d) 27. Resonance structures of a molecule have (a) same arrangement of atoms (b) different arrangement of atoms (c) same number of paired electrons (d) different number of paired electrons Answer. (a) and (c) 28. Which of the following compounds have planar molecules? (a) ethyl alcohol (b) formaldehyde (c) diethyl ether (d) 1,3-butadiene Answer. (b) and (d) 29. Which of the following compounds will show dipole moment? (a) cis-1,2-dichloroethylene (b) o-dichlorobenzene (c) trans-1,2-dichloroethylene (d) p-dichlorobenzene Answer. (a) and (b) 30. Which molecule has a nonzero dipole moment? (a) Cl 2 (b) CO 2 (c) CCl 4 (d) CHCl 3 Answer. (d) 31. Which of the following compounds have lowest dipole moment? (a) carbon tetrachloride (b) chloromethane (c) dichloromethane (d) chloroform Answer. (a) 32. Which molecule has the greatest dipole moment (a) CH Cl 3 (b) CH Br 3 (c) CH F 3 (d) CH I 3 Answer. (c) 33. Which of the following compounds have highest dipole moment? (a) dichloromethane (b) chloroform (c) chloromethane (d) carbon tetrachloride Answer. (a) 34. Homolytic fission of C–C bond leads to the formation of : (a) Free radicals (b) Carbonium ions (c) Carbanions (d) None of these Answer. (a) 35. Homolytic fission of covalent bond between carbon atoms will produce : (a) Two carbonium ions (b) Two molecules (c) Free radicals (d) Carbonium ion and carbanion Answer. (c) 36. The order of stability of carbonium ions is (a) tertiary > secondary > primary (b) secondary > tertiary > primary (c) primary > secondary > tertiary (d) primary > tertiary > secondary Answer. (a)