311Exam2Key2015 - CHE 311 EXAM 2 KEY(CH 5-10 Answers in...

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Unformatted text preview: CHE 311 EXAM 2 KEY (CH. 5-­‐10) Answers in BOLD RED MULTIPLE CHOICE (60%; 2% each) Mark the letter of the BEST answer to each question clearly on your answer sheet. Thank you! 1. What is the proper IUPAC name for the alkene shown at the right? A. (Z)-­‐2-­‐methyl-­‐2-­‐pentene B. 1,3-­‐dimethyl-­‐2-­‐pentene C. (E)-­‐1,3-­‐diemthyl-­‐1-­‐butene D. (Z)-­‐3-­‐methyl-­‐2-­‐pentene 2. Which C8H16 isomer should be the most stable one? A. 1-­‐octene B. trans-­‐4-­‐methyl-­‐3-­‐heptene C. cis-­‐3,4-­‐dimethyl-­‐3-­‐hexene D. trans-­‐3-­‐octene 3. Elimination reaction of 2-­‐hexanol (CH3CH(OH)CH2CH2CH2CH3) requires heat and ____________ and gives mostly: A. acid ; 1-­‐hexene B. base ; cis-­‐2-­‐hexene C. base ; trans-­‐2-­‐hexene D. acid ; trans-­‐2-­‐hexene 4. Dehydrohalogenation of alkyl halides using alkoxides occurs by an ______ mechanism and ________ carbocations A. E2 ; involves B. E2 ; does not involve C. E1 ; involves D. E1 ; does not involve 5. Which process is most likely to involve a structural change due to carbocation rearrangement? A. dehydrohalogenation of 2-­‐bromo-­‐3-­‐methylbutane B. dehydrohalogenation of 2-­‐bromopentane C. dehydration reaction of 3-­‐methyl-­‐2-­‐butanol D. dehydration reaction of 2-­‐pentanol 6. Carbocations are formed during which type of alkene reaction? A. hydrogenation B. acidic hydration C. hydroboration-­‐oxidation D. ozonation 7. If we react 1-­‐methylcyclohexene with B2H6 and then aqueous basic H2O2 the major product formed will be C CH3 CH3 CH3 CH3 A.''''''''''''''''''''''''''''''''''''''B.''''''''''''''''''''''''''''''''''''''C.''''''''''''''''''''''''''''''''''''D. OH OH O OH 8. To produce 1-­‐bromobutane from 1-­‐butene, the best route is to react 1-­‐butene with: A. Br2 + H2O2 B. HBr + peroxides C. CH3COOOH; then HBr D. B2H6 + Br2 9. When you react 2-­‐pentene with ozone in the presence of Zn and acetic acid, the products are A. methanol and 1-­‐butanol B. two aldehydes C. an aldehyde + a ketone D. two carboxylic acids 10. The reaction of alkenes with bromine tends to produce only products in which the Br’s added… A. syn B. anti C. all at once D. after forming free radicals The following structures are used in questions 11-­‐14 NH2 C13H27 O OH OH HOH2C H3 C CH2OH O H HOH2C H3C CH3 H CH3 H HO OH OH H H )I)))))))))))))))))))))))))))))))))))))II))))))))))))))))))))))))))))))))III))))))))))))))))))))))))))))))))))))))))))))IV CH 3 11. How many chirality centers are there in structure I? A. none B. 1 C. 3 12. What is the stereochemistry of the rightmost chiral carbon in structure II? A. S B. R 13. How many stereoisomers of structure IV could exist? A. 3 B. 16 C. 6 14. What term most precisely describes the relationship between structures II and III? A. diastereomers B. enantiomers C. optical isomers D. meso forms 15. A polymer is generated which has a repeating [–CH2–CH(CH2CH3)–] structure. If all the methine groups are R, A. it is isotactic B. it is atactic C. it is syndiotactic D. it is mesotactic 16. When attempting a nucleophilic substitution of an alkyl halide using hydroxide, what will be most successful? A. using high temperatures B. using a primary halide C. using excess OH– D. using a tertiary halide D. 2 D. 8 CHE 311 Exam 2 KEY Page 2 17. In contrast to the conditions in question 16, what will produce the highest alkene yield from that reaction? A. using a primary halide B. using high temperatures C. using polar solvent D. using a tertiary halide 18. What category of reaction MOST benefits from the use of polar aprotic solvents with alkyl halides? A. SN1 B. SN2 C. E1 D. E2 19. Which of the following anions is a good nucleophile (Lewis base) but a poor Brønsted-­‐Lowry base? A. OH– B. I– C. CH3O– D. F– 20. If 3-­‐methyl-­‐3-­‐hexanol is treated with HBr and warmed gently, the major reaction type that occurs is: A. SN2 B. SN1 C. E2 D. E1 21. Klein points out basicity and nucleophilicity are not always parallel, but are at times; when are they parallel? A. when the species compared all have the same charge B. when comparing atoms in the same group C. when the species compared are all water soluble D. when comparing atoms in the same period 22. When we wish to convert 3-­‐hexyne into cis-­‐3-­‐hexene, the best reagent(s) to use for the reduction is(are): A. NaNH2 B. Na in NH3(l) C. H2 + Pt D. H2 + Lindlar catalyst 23. Alkenes & alkynes react in essentially identical ways, giving products with the same structural changes, with: A. HBr + peroxides B. ozone C. B2H6; then H2O2+OH– D. H3O+ 24. The major final product formed by the reaction of a terminal alkyne with B2H6; then H2O2+OH– is : A. an alkene B. an aldehyde C. a ketone D. an alcohol 25. Which conditions are NOT able to convert vicinal dihalides into alkynes? a. NaNH2 in NH3(l) B. K+ –O-­‐t-­‐Butyl in DMSO C. 5.0 M KOH(aq) 26. Which diene will give off the LEAST energy when it is reduced using H2 + Pt to form pentane? A. 1,3-­‐pentadiene B. 1,2-­‐pentadiene C. 1,4-­‐pentadiene D. all give off the same energy 27. Dienes undergo electrophilic addition, often forming two different possible products. This can usually be controlled by the use of proper temperature ranges to produce mostly the desired isomer. Under so-­‐called kinetic conditions, the _____________________ product forms, while under thermodynamic conditions it is the ______________________ isomer which is produced. A. higher EACT ; more endothermic ∆Hf B. lower EACT ; more endothermic ∆Hf C. higher EACT ; more exothermic ∆Hf D. lower EACT ; more exothermic ∆Hf 28. In order to produce mostly 3-­‐bromocyclopentene from cyclopentene, react it in a 1:1 molar ratio with A. Br2 in CCl4 B. aqueous HBr C. NBS in CCl4 D. aqueous Br2 29. Diels-­‐Alder reactions are pericyclic reactions, which characterized by all the following EXCEPT they aren’t: A. concerted B. symmetry forbidden C. reactions with cyclic transition states D. one step reactions 30. What is the product of this Diels-­‐Alder reaction? Answer C F F + F D. conc. KOH in hot ethanol F F F F PROBLEMS (40%; 12, 12, and 16%) F F F A$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$B$$$$$$$$$$$$$$$$$$$$$C$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$D I. DRAW OUT THE MECHANISM of the addition of HBr to 1-­‐butene, including the structure of the major product; explain why the major product has the structure that it does, in terms of the mechanism you drew. H Br slow fast Br– The/mechanism/involves/attack/by/the/alkene/π/electrons/on/the/HBr to/form/a/carbocation./In/the/type/of/situation/shown,/the/carbocation formed/will/be/the/most/stable/one/possible/(secondary/here)./This/is the/reason/that/the/product/has/Br/at/the/more/subsitituted/carbon/of the/original/alkene./The/bromide/quickly/adds/to/the/cation. Br CHE 311 Exam 2 KEY Page 3 II. Define what a racemic mixture is, and explain how the use of the term resolution relates to such mixtures. Explain how the process of resolution could be carried out upon a racemic mixture. A racemic mixture is made up of equal amounts of both enantiomers of a chiral molecule. Because the two isomers are present in equal quantities, the overall mixture has no net effect on plane-­‐polarized light, so it appears to be optically inactive. Resolution in this context means the process of separating the two isomers from one another. The usual way this is done is to react both enantiomers with one pure enantiomer of some other substance (for example, if the racemic substances are bases, you use a pure enantiomer of some acid). Because the resulting products have two DIASTEREOMERS as their products, and diastereomers have different physical properties, like solubilities or melting points, they can be separated and the original enantiomers can then be regenerated by reversing the resolving reaction (as, for example, by the basification of the resolution products obtained by the reaction referred to earlier). III. DRAW THE STRUCTURE of each of the products that would come from these alkyne reactions. a. H Hg+2,&H3O+ (a$ketone) O b. 1.#O3 2.#H2O COOH + HOOC CH3 ozonation,of,alkynes,forms,acids c. Na,$NH3(l) Dissolving)metal)reduction gives)the)trans3alkene)product ...
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