Unformatted text preview: CHE 311 EXAM 2 (Ch. 5-‐10) KEY Answers in BOLD RED Multiple Choice(64%; 2% each) 1. Please mark the letter of the BEST answer to each question clearly on your answer sheet. Thanks! Which of these is 1-‐Bromo-‐6-‐methylcyclohexene? Answer D (others are 3,4 / 1,3 / and 1,2-‐bromo-‐methyl) Br Br Br a.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%b.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%c.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%d.
Br 2. Which of these C6H12 alkenes will release the MOST energy when hydrogenated to form hexane? a. (E)-‐2-‐hexene b. 1-‐hexene c. (Z)-‐2-‐hexene d. (E)-‐3-‐hexene 3. When the alkyl halide 3-‐Bromo-‐3-‐methylpentane is subjected to E2 elimination, the main product will be: a. 3-‐Methyl-‐1-‐pentene b. (Z)-‐3-‐Methyl-‐2-‐pentene c. (E)-‐3-‐Methyl-‐2-‐pentene d. 2-‐Ethyl-‐1-‐butene 4. Methylenecyclohexane (shown at the right) can be made from one specific alkyl bromide by E2 elimination. What alkyl bromide would that be? a. 1-‐Bromo-‐1-‐methylcyclohexane b. 1-‐(bromomethyl)cyclohexane c. 2-‐Bromo-‐1-‐methylcyclohexane d. 1-‐(dibromomethyl)cyclohexane 5. When 2,2-‐dimethyl-‐1-‐hexanol is heated in sulfuric acid, one product is 2-‐methyl-‐2-‐hexene, which must form a. by E1 elimination involving a carbocation rearrangement b. by simple E2 elimination of water c. by E2 elimination involving a carbocation rearrangement d. by simple E1 elimination of water 6. The replacement of all alkane H by D in 2-‐butanol will lead to a ____________ elimination by an _____ mechanism. a. slower ; E2 b. slower ; E1 c. faster ; E2 d. faster ; E1 7. Counting both structural and stereo-‐isomers, how many alkenes yield 2,3-‐dimethylbutane on hydrogenation? a. four b. one c. two d. three 8. 1-‐Butene + HBr + peroxides will give ________________ as the major organic product. a. 2-‐bromobutane b. 2-‐bromo-‐1-‐butanol c. 1-‐bromobutane d. 1-‐bromo-‐2-‐butanol 9. Alkenes can be converted to alcohols by all the following reagents EXCEPT for: a. B2H6 ; then OH–, H2O2 b. dilute aqueous H2SO4 c. O3 in water d. conc. H2SO4 ; then H2O 10. If we react mixed (E)-‐ & (Z)-‐3,4-‐Dimethyl-‐2-‐pentene with Br2 in H2O, the major organic product(s) will be: a. enantiomers of 2-‐bromo-‐3,4-‐dimethyl-‐3-‐pentanol b. enantiomers of 3-‐bromo-‐3,4-‐dimethyl-‐2-‐pentanol c. enantiomers of 2,3-‐dibromo-‐3,4-‐dimethylpentane d. meso 2,3-‐dibromo-‐3,4-‐dimethylpentane 11. What sequence of reactions would allow you to do the conversion shown at the right? Choose the best match that is likely to give reasonably high yields of the desired product. a. KOH in ethanol + heat ; then O3 with Zn in acetic acid b. H2SO4 + heat ; then B2H6; then H2O2 + OH– c. H2SO4 + heat ; then peroxyacetic acid (CH3COOOH) d. KOH in ethanol + heat ; then H3O+ and gentle warming 12. Which of the following species is chiral? a. CH3CHBrCH=CH2 b. CH3CH=CHCH2Br 13. 2,3-‐pentanediol and 2,4-‐pentanediol are isomers; the first has _____ and the second has ______ stereoisomers. a. 2 ; 3 b. 4 ; 4 c. 4 ; 3 d. 4 ; 6 14. The relationship of the two structures shown on the right is that they are… a. enantiomers of one another b. the same structure from two perspectives c. diastereomers (chiral but not enantiomers) d. structural isomers but not stereoisomers O
OH c. ClCH2CH2CH2OH HO H d. ClCH2CH(OH)CH2Cl H OH CHE 311 Exam 2 Page 2 CH2OH 15. Knowing how a Fischer projection represents stereochemistry, what will be the absolute configuration of the substance shown at the right side of this question? a. it is not chiral b. R, R c. S d. R 16. What is the relationship between R and S stereochemistry and the rotation of plane-‐polarized light? a. R enantiomers rotate light to the right b. R & S enantiomers both rotate light to the right c. R enantiomers rotate light to the left d. there is no correlation of R & S with direction of rotation 17. When (R)-‐2-‐bromobutane is treated with NaI in acetone, the major organic product will be a. (S)-‐2-‐iodobutane b. (R)-‐2-‐iodobutane c. racemic 2-‐bromobutane d. no reaction occurs 18. 1-‐, 2-‐, and 3-‐chlorohexane are reacted with NaI in acetone. Which one will react most rapidly? Will this be an SN1 or an SN2 reaction considering the reagent and solvent used? a. 3-‐chlorohexane ; SN1 b. 1-‐chlorohexane ; SN1 c. 1-‐chlorohexane ; SN2 d. 3-‐chlorohexane ; SN2 19. When an alkyl halide is reacted with a reagent and the product(s) have an altered carbon skeleton, the most likely mechanism(s) to be involved in the reaction(s) would be a. E1 or SN1 b. SN1 or SN2 c. E2 or SN2 d. E1 or E2 20. What would be a good way to convert t-‐butyl chloride into isobutyl iodide (1-‐iodo-‐2-‐methylpropane)? a. heat + CH3O–Na+ ; then HI + peroxides b. heat + H2SO4 ; then B2H6 ; then OH–, H2O2 ; then HI + heat c. heat + CH3O–Na+ ; then HBr + peroxides ; then NaI in acetone d. heat + H2SO4 ; then H2O ; then HI + heat 21. (R)-‐2-‐pentanol is treated with 6M HBr, forming a mixture of (R)-‐ and (S)-‐2-‐bromopentanol. What happened? a. SN1 reaction only b. SN2 reaction only c. E2, then addition reaction d. SN1 & SN2 reactions 22. 2-‐Methyl-‐2-‐pentanol is heated in H2SO4. The conditions and lack of a base favor E1 reaction, forming a major organic product of ___________________ and a minor organic product of _____________________. a. 2-‐methyl-‐2-‐pentene ; 2-‐methyl-‐1-‐pentene b. 2-‐methyl-‐2-‐pentene ; trans-‐2-‐hexene c. 2-‐methyl-‐1-‐pentene ; cis-‐2-‐hexene d. 2-‐methyl-‐1-‐pentene ; trans-‐4-‐methyl-‐2-‐pentene 23. Alkylation of acetylide ions has specific limits upon how it may be performed. One of these is that a. the alkyl halide is 3° b. the alkyne must be internal c. H2O is the solvent d. the alkyl halide is 1° or CH3-‐ 24. The best reagent to convert 3-‐hexyne into (Z)-‐3-‐hexene would be a. limited H2 + Pt b. H2 + Lindlar catalyst c. Na in NH3(l) 25. 26. If 2-‐hexyne is reacted with aqueous acid plus Hg2+ salts, two products form. They would be 27. Alkynes which form by elimination reactions can be produced from all the following EXCEPT: a. vicinal dihalides b. geminal dihalides c. cumulated dienes d. vicinal diols 28. A simple conversion of propene into allyl alcohol in good yield would involve a. NBS in warm CCl4 ; then NaOH(aq) b. HBr + peroxides ; then KOH in hot ethanol c. Br2 in CCl4 ; then NaOH(aq) d. Br2 in CCl4 ; then KOH in hot ethanol 29. If we want to convert 1,3-‐butadiene into mostly 3-‐bromo-‐1-‐butene, the best conditions are a. HBr at 5°C b. HBr at 80°C c. Br2 at 5°C d. Br2 at 80°C 30. Diels-‐Alder reactions work best with a dieneophile that has _________________ on it a. only C and H b. electron-‐donating groups c. electron-‐withdrawing d. aromatic 31. For successful cycloaddition reactions to occur thermally, there could be ______ or ______ pi electrons involved a. 4 ; 6 b. 6 ; 8 c. 6 ; 10 d. 6 ; 9 32. The basic principle of the Frontier Orbital approach to explaining reactions is that electrons come from a. dienes b. nonbonding orbitals c. LUMO’s d. HOMO’s a. I and II b. I and III c. I and IV O H3C Br H H CH3 d. B2H6 in diglyme O d. II and III O
I##############################################II#############################################III########################################IV Reaction of 3-‐hexyne with ozone and water gives one major organic product: a. CH3CH=CH2 b. CH3CH2COOH c. CH3CH2CH2OH d. CH3CH2C(=O)H CHE 311 Exam 2 Page 3 Problems (36% ; 12% each) Answer each clearly and completely as requested. Note that it is possible to use somewhat varied reagents for questions I and III and still be correct. I. We discussed TWO major methods of alcohol synthesis in Ch. 6. Using 1-‐butene as your starting material, give the proper reagents and conditions to convert it selectively to 1-‐butanol and also to 2-‐butanol. H3O+
OH II. H
H III. CHO
OH H H (R) HO (S) H H (R) OH OH OH
same)as H HO
OHC OH H CH2OH H2C OH CH2OH Starting with the terminal alkyne and alcohol shown, show how you would combine them to give the product you see as the target. This will require that the alcohol be converted into a sulfonate ester and the alkyne be converted into an acetylide. Give the reagents and steps to do these transformations and the final reaction. and H OH D-‐Xylose, shown below, is a carbohydrate first found in wood. CIRCLE any chiral carbons and label as R or S CHO H2O2-+-OH– B2H6
ether-solvent OH NaNH2%in%NH3(l) H O
OH O O
S + Na+ Cl S –%HCl then...
Na+ O O
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