Organic Chemistry Alkene Reactions: Reagents, Products, and Stereochemistry

H2SO4, heat (neat) on an alcohol

E1 dehydration. Makes an alkene + H2O. Carbocation intermediate, Zaitsev (trans major). Reversible, heat drives it forward. Rearrangements possible.

NaOEt, EtOH (or NaOMe, OH-) on an alkyl halide

E2 with a small base. Makes the MORE substituted alkene (Zaitsev). Needs anti-coplanar beta H and LG.

KOtBu / tBuOH (or LDA) on an alkyl halide

E2 with a big bulky base. Makes the LESS substituted alkene (Hofmann).

H2, Pd/C (or Pt, Raney Ni)

Hydrogenation. Adds H and H to the alkene. Syn addition. Stereospecific.

HCl, HBr, HI

Markovnikov addition. H goes on the less substituted C, X on the more substituted C. Carbocation, so racemic and rearrangements are possible. Not stereoselective.

H3O+ (or cat. H2SO4, H2O / TsOH)

Hydration. Markovnikov H and OH (OH on the more substituted C). Carbocation, so racemic, rearrangements possible, and alkene isomerization (E1) competes. Low T favors addition, high T favors E1.

Br2, CCl4 (or Cl2, I2; NOT F2)

Adds X and X across the alkene. Anti addition via a cyclic bromonium ion. Stereospecific. Regioselectivity N/A. Product is a dihalide.

Br2, H2O (or X2, H2O)

Halohydrin. Adds X and OH. Anti addition, Markovnikov (OH goes on the more substituted C). Same bromonium ion, water attacks.

Halohydrin + NaNH2

Makes an epoxide. The base deprotonates the OH, then the O- does SN2 on the C-Br carbon.

1) Hg(OAc)2, H2O 2) NaBH4, H2O, NaOH

Oxymercuration-demercuration. Markovnikov H and OH. NO carbocation rearrangements (mercurinium ion). Step 1 is anti, but NaBH4 scrambles the C that held Hg, so overall racemic mix of syn and anti.

1) BH3, THF 2) H2O2, NaOH

Hydroboration-oxidation. Anti-Markovnikov H and OH (OH on the LESS substituted C). Syn addition. No rearrangements. Stereospecific.

mCPBA

Epoxidation. Makes an epoxide. Syn addition of O, racemic.

NaOCl (bleach) + Jacobsen's catalyst

Enantioselective epoxidation. Makes one enantiomer of the epoxide (OA).

Epoxide + H3O+

Epoxide opening. Water attacks from the back. Anti addition, makes an anti-diol. Stereospecific.

Cat. OsO4, H2O2

Dihydroxylation. Adds OH and OH to the same face. Syn addition, makes a syn-diol. Regioselectivity N/A.

1) O3, -78 C 2) Me2S (or NaHSO4)

Ozonolysis, reductive workup. Breaks C=C, replaces with two C=O. Keeps all substituents. H on the alkene C stays as an aldehyde H.

1) O3, -78 C 2) H2O2

Ozonolysis, oxidative workup. Breaks C=C into C=O pieces. Any H on the alkene C turns into OH (aldehyde becomes carboxylic acid).

HBr, ROOR (peroxides)

Anti-Markovnikov HBr addition. Br goes on the LESS substituted C. Radical reaction. Both syn and anti addition.