Chapter 16 — Exercises
Fifty problems on the alkene addition toolbox. Drawing required wherever a structure or mechanism is asked for. ∗ marks problems with full worked solutions in Appendix Answers to Selected Exercises.
Section A — Predicting products with each reagent
16.1∗ (routine) Predict the product of 2-methyl-2-butene with each reagent: (a) H₂O / dilute H₂SO₄ (b) Hg(OAc)₂ / H₂O, then NaBH₄ (c) BH₃ · THF, then H₂O₂ / NaOH (d) Br₂ in CCl₄ (e) Br₂ in H₂O (f) mCPBA (g) OsO₄ / NMO (h) O₃, then Zn / HOAc (i) O₃, then H₂O₂ (j) H₂ / Pd / C
16.2 (routine) Repeat 16.1 for cis-2-pentene. Specify stereochemistry where applicable.
16.3∗ (moderate) Predict the product of styrene (PhCH=CH₂) with: (a) H₂O / H⁺ (b) BH₃ / H₂O₂ (c) Br₂ (d) mCPBA (e) OsO₄
16.4 (moderate) Predict the product of cyclohexene with: (a) Br₂ / CCl₄ (b) Br₂ / H₂O (c) mCPBA, then HBr (epoxide opening) (d) OsO₄ (e) O₃ / Zn
16.5 (challenge) A natural product has a tetrasubstituted alkene. Which reagents react with it efficiently? Which fail?
Section B — Choosing the right reagent
16.6∗ (routine) Choose a reagent to make: (a) a Markovnikov alcohol (no rearrangement). (b) an anti-Markovnikov alcohol with syn stereochemistry. (c) a syn-1,2-diol. (d) an anti-1,2-diol. (e) an epoxide. (f) a vicinal dibromide. (g) a saturated alkane.
16.7 (routine) Why is oxymercuration preferred over acid-catalyzed hydration when the substrate has a quaternary carbon nearby?
16.8 (moderate) A substrate has both an alkene and a ketone. Choose hydrogenation conditions that reduce only the alkene, leaving the ketone intact.
16.9 (moderate) A substrate has both an alkene and an ester. Choose oxidation conditions that give a syn-diol without affecting the ester.
16.10 (challenge) Design a synthesis of (R)-1-phenylethanol from styrene using a Sharpless-style asymmetric reaction.
Section C — Mechanism
16.11∗ (routine) Draw the mechanism of acid-catalyzed hydration of propene → 2-propanol. Show each step with arrows.
16.12 (routine) Draw the mercurinium ion intermediate of Hg(OAc)₂ + propene. Why does water attack the more-substituted C?
16.13 (moderate) Draw the four-centered TS of hydroboration of propene with BH₃. Identify which C the B goes to and why.
16.14 (moderate) Draw the bromonium ion intermediate of Br₂ + propene + H₂O → propenebromohydrin. Why does water attack at the more-substituted C?
16.15 (challenge) Draw the cyclic osmate ester intermediate of OsO₄ + propene → diol. Why is the diol cis?
Section D — Stereochemistry
16.16∗ (routine) For each reaction with cyclohexene, predict the stereochemistry: (a) Br₂ → ? (b) BH₃ / H₂O₂ → ? (c) OsO₄ → ? (d) mCPBA → ? (e) H₂ / Pd → ?
16.17 (moderate) Hydroboration-oxidation gives syn addition. Is the OH ending up on the same face as the H, or opposite? Explain.
16.18 (moderate) Why does mCPBA give a stereospecific epoxide (cis-alkene → cis-epoxide; trans → trans)?
16.19 (challenge) A chiral alkene + Br₂ gives a chiral 1,2-dibromide. Use the bromonium-ion mechanism to predict the relationship between alkene and product chirality.
Section E — Halohydrins and epoxides
16.20∗ (routine) Predict the product of: 2-methylpropene + Br₂ + H₂O → ?
16.21 (routine) Convert a halohydrin to an epoxide. What conditions?
16.22 (moderate) Open an epoxide with various nucleophiles: (a) MeOH / H⁺ (b) MeNH₂ (c) NaSH
What product results in each?
16.23 (challenge) Sharpless asymmetric epoxidation: allylic alcohol + TBHP + Ti(OiPr)₄ + chiral DET. Predict the chirality of the epoxide product.
Section F — Diols and asymmetric dihydroxylation
16.24∗ (routine) OsO₄ + NMO + cyclohexene → cis-1,2-cyclohexanediol. Sketch the chair conformation.
16.25 (routine) Sharpless asymmetric dihydroxylation: AD-mix-α gives one enantiomer; AD-mix-β gives the other. Predict the product of: styrene + AD-mix-α.
16.26 (moderate) Compare KMnO₄ (cold, dilute) vs OsO₄ + NMO for syn-dihydroxylation. What are the trade-offs?
16.27 (challenge) Modern catalytic AD uses ~0.1 mol% OsO₄ + chiral ligand + NMO. Why is the substoichiometric Os possible?
Section G — Ozonolysis
16.28∗ (routine) Predict the products of: (a) 2-methyl-2-butene + O₃ + Zn / HOAc → ? (b) (E)-3-hexene + O₃ + Me₂S → ? (c) cyclohexene + O₃ + H₂O₂ → ?
16.29 (moderate) Use ozonolysis to determine the structure of an unknown alkene that gives acetaldehyde + 2-methylpropanal upon reductive workup. Which alkene was it?
16.30 (challenge) Ozonolysis of a 1,3-cyclohexadiene gives a dialdehyde. Sketch the mechanism for both alkenes opening.
Section H — Hydrogenation
16.31∗ (routine) Hydrogenation with H₂/Pd/C reduces: (a) C=C ✓ (b) C≡C ✓ (to alkane) (c) C=O? (depends on conditions; usually no for ketones at low T)
16.32 (routine) Lindlar Pd reduces alkynes to cis-alkenes (Ch 17). Why is the cis selectivity stereospecific?
16.33 (moderate) Compare Pd/C, PtO₂ (Adams), and Raney Ni for reducing alkenes. Which is most aggressive?
16.34 (challenge) Asymmetric hydrogenation: Rh-(R,R)-DiPAMP + α,β-unsaturated acid → chiral acid (Knowles, Nobel 2001). Sketch the principle.
Section I — Multistep synthesis
16.35∗ (routine) Design a synthesis of 2-pentanol from 1-pentene. Use acid-catalyzed hydration.
16.36 (routine) Design a synthesis of 1-pentanol from 1-pentene. Use hydroboration-oxidation.
16.37 (moderate) Design a synthesis of trans-1,2-cyclohexanediol from cyclohexene. (Hint: epoxide + acid hydrolysis.)
16.38 (moderate) Design a synthesis of cis-1,2-cyclohexanediol. (Hint: OsO₄.)
16.39 (challenge) Design a synthesis of cyclohexanecarboxylic acid from cyclohexene via a 3-step route.
16.40 (challenge) Design a synthesis of (R)-3-methylcyclohexan-1-ol from a suitable alkene + asymmetric methods.
Section J — Industrial applications
16.41 (routine) Margarine production: hydrogenation of vegetable oils. Explain the chemistry. Why are trans fats a concern?
16.42 (moderate) Industrial production of ethylene oxide (precursor to ethylene glycol): epoxidation of ethylene + Ag catalyst + O₂. Sketch the chemistry.
16.43 (challenge) Industrial production of glycerol from propylene: 3 steps via allyl chloride + epichlorohydrin + hydrolysis. Sketch each step.
Section K — Spectroscopy
16.44∗ (routine) A reaction starts with an alkene (IR 1640, ¹H NMR 5.2 ppm) and ends with: IR 3300 (broad), ¹H NMR 3.5 (CH-OH). What was the reaction?
16.45 (moderate) A reaction starts with an alkene and ends with a 1,2-dibromide (¹³C peaks at 50-60 for both C-Br carbons). Identify the reagent.
16.46 (challenge) A complex molecule's IR shows a new peak at 870 cm⁻¹. This is diagnostic for an epoxide ring. What was the reagent?
Section L — Open-ended
16.47 (challenge) Compare the alkene addition toolbox to a similar one for alkynes (Ch 17). What's the same? What's different?
16.48 (challenge) Modern asymmetric methods (Sharpless, Jacobsen, Noyori) revolutionized alkene chemistry. Explain how each works in 1-2 sentences.
16.49 (challenge) Design a 5-step synthesis of a complex natural product using only alkene addition reactions from this chapter.
16.50 (challenge) A target has both alkenes and other functional groups. Plan the order of alkene reactions to avoid affecting the other groups. Use chemoselectivity arguments.
Notes for instructors: Common stumbling blocks for Chapter 16: (1) Mismatching reagent with regio/stereo outcome. (2) Forgetting carbocation rearrangements. (3) Confusing syn (OsO₄, BH₃, mCPBA, H₂/Pd) with anti (Br₂, mCPBA + acid hydrolysis). (4) Not appreciating chemoselectivity for complex substrates. Computational exercises: predict the products of various alkene + reagent combinations, then verify with a synthesis textbook.