Organic Chemistry Solved Lab Questions, Lab Reports of Organic Chemistry

Download Organic Chemistry Solved Lab Questions and more Lab Reports Organic Chemistry in PDF only on Docsity! Organic Chemistry 32-235 Practice Questions for Exam #2 Part 1: (Circle only ONE choice, circling more than one will be counted as wrong!) 4 points each 1. The correct IUPAC name for the following compound is: (A) (1R, 3R)-1-chloro-3-methylcyclohexane (B) (1R, 3S)-1-chloro-3-methylcyclohexane (C) (1S, 3S)-1-chloro-3-methylcyclohexane (D) (1S, 3R)-1-chloro-3-methylcyclohexane (E) None of the above. The Key here is to determine the configuration R or S for each chiral carbon. The answer here is 1S, 2S. 2. Consider the SN1 reaction of tert-butyl chloride with iodide ion: (CH3)3C Cl + I (CH3)3C I Cl+ If the concentration of iodide ion is doubled, the rate of forming tert-butyl iodide will: (hint: consider mechanism, i.e. how is the product formed?) (A) Double. (B) Increase 4 times. (C) Remain the same. (D) Decrease. (E) None of the above. In SN1 reaction, the rate is independent of the nucleophile involved since the nucleophile is not involved in the rate determining step. Thus the anwer is C. 3. The relationship between the following two structures is: (A) enantiomers (B) diastereomers (C) structural isomers (D) identical (E) none of the above The key here is to know the definition of all terms and then determine R or S configuration for each chiral carbon. The answer is (B) (by definition) 4. The specific rotation of pure (R)-2-butanol is -13.5°. What % of a mixture of the two enantiomeric forms is (S)-2-butanol if the specific rotation of this mixture is −5.4° ? (A) 40% (B) 30% (C) 60% (D) 70% (E) None of the above The answer is B since e.e. is 40% favoring R. (5.4/13.5=40%) CH3H Cl H CH3 H OH OHH CH3 CH3 HO H OHH CH3 Page 2/9 5. Which of the following alkyl halides would undergo SN2 reaction most rapidly? (A) CH3CH2-Br (B) CH3CH2- Cl (C) CH3CH2-I (D) CH3CH2-F (E) they react at the same rate In Sn2 reaction, the nucleophile attacks from the back of the leaving group. The better the leaving group, the easier it is to leave (faster rate). The answer is C since iodide ion is the best leaving group. 6. Which of the following molecules is chiral ? CH3 CH3 H H CH3 H H CH3 OH CH3 (A) (B) (C) C C CH3 H CH3 H C C H CH3 CH3 H (D) (E) Go by definition or look for plane of symmetry/point of inversion. The answer is B. 7. The relationship between (A) and (B) structures in the previous question is: A) identical B) structural isomers C) diastereomers D) enantiomers E) None of the above Again need to know terms and how to apply them. The answer is C. Page 5/9 15. Which is the least stable in these structures if the radical carbon is changed to a carbanion? (answer is A, pay attention to sign of charge!) 16. The major monobromination product in the following reaction is (CH3)3CCH2CH3 + Br2 products hν (CH3)3CCH2CH2Br (CH3)3CCHCH3 Br (CH3)2CCH2CH3 Br (CH3)2CCH2CH3 CH2Br(a) (b) (c) (d) (e) none of the above The answer is (C) because selectivity is high for bromination which prefers to attach the weaker C-H bond. 17. According to the following energy profile, the rate of reaction from A to B is determined by E reaction coordinate A B C (a) the energy of A only (b) the energy of B only (c) the energy difference between C and A (d) the energy difference between B and A (e) the energy of C only The answer is C (activation energy) Page 6/9 18. The bond dissociation energy is the amount of energy required to break a bond a) so as to produce the more stable pair of ions b) heterolytically c) homolytically d) via hydrogenation e) none of the above Definition: homolytically 19. Given the bond dissociation energies below (in kcal/mol), calculate the overall ∆H° for the following reaction: (CH3)3CH + Br2 (CH3)3CBr + HBr (CH3)3C-H 91 (CH3)3C-Br 65 Br-Br 46 H-Br 88 CH3-Br 70 ∆H° = -16 kcal/mol Write chain propagation steps for the above bromination reaction. (CH3)3CH + Br (CH3)3CBr + Br (CH3)3C + HBr (CH3)3C + Br2 End of Part 1 Page 7/9 Part 2: 1. (14 pt) Draw the organic product expected from each of the following reactions. Be sure to indicate stereochemistry where appropriate and to include stereoisomers if any. In case two or more stereoisomers are formed, label their relationship as diastereomers, enantiomers, structural isomers, or conformers. 2. (10 pt) (A) Draw Fisher projections for (2R, 3S)-2-bromo-3-chlorobutane and (2S, 3R)-2-bromo- 3-chlorobutane, with the carbon chain on the vertical line. Label each structure as (2R, 3S) or (2S, 3R). (B) Assume that you have a mixture of equal amount of each of the above compounds. Can they be separated into two containers based on physical properties such as b.p., m.p., etc.? If yes, which technique would you use? If no, briefly explain why not. The two compounds as drawn are enantiomers which have identical b.p. and other physical properties (different only towards plane polarized light). Therefore they can't be separated based on physical properties alone. I + NaO C O CH3 SN2(A) CH3 O CO C Cl H CH3 D + NaOCH3 SN2 (B) CCH3O H CH3 D C I CH3CH2 CH3 CH3CH2CH2 H2O + SN1 (C) C OH CH3CH2 CH3 CH3CH2CH2 CHO CH3CH2 CH3 CH3CH2CH2 + about 50% of each CH3 H Br ClH CH3 2S, 3R CH3 HBr Cl H CH3 2R, 3S