Reactions of Alkenes: Summary Intermediate: Carbocation Regiochemisty: Markovnikov* Anti-Markovnikov* Addition: Rearrangements? Radical 3-Membered Ring None or Cyclic (concerted) Markovnikov-like N/A Syn & Anti Syn & Anti Anti Syn yes no no no *the reaction goes through the pathway of the most stable intermediate; the more substituents on an electron deficient carbon (carbocation or radical), the greater its stability Stereochemistry: • If the reactants are optically inactive (achiral), the products will be optically inactive (achiral, racemic or meso) • If the reactants are optically active (chiral), the products will be optically active (unequal mixture of enantiomers, unequal mixture of diastereomers, or 1 enantiomer) • Use 2n of the product to predict the maximum number of stereoisomers (if just anti or just syn addition, divide the maximum number of stereoisomers by 2) Predicting the type of intermediate: • Carbocation - H is the electrophile (no lone pair to share with the empty p orbital) • Radical - an initiator with a weak bond (ex. ROOR) and an energy source (heat or light) is present • 3-Membered Ring - the electrophile has a lone pair of electrons available to share with the empty p orbital • None or Cyclic - the electrophile can both accept and donate electrons at the same time HX (X = Br, Cl, I) CH3 heat or light (NOT HCl or HI) Br (X = Br, Cl) (X = Br, Cl) CH3 X X CH3 OH X H3O+, H2O OH CH3 Alkyl halide Radical syn + anti Anti-Markovnikov Vicinal dihalide 3-membered ring anti Markovnikov-like Halohydrin 3-membered ring anti Markovnikov-like Alcohol Carbocation syn + anti Markovnikov Alcohol 3-membered ring anti Markovnikov-like Alcohol None (concerted) syn Anti-Markovnikov H3C 1. Hg(OAc)2, H2O 2. NaBH4 OH H3C 1. BH3, THF CH3 Markovnikov CH3 X2, H2O CH3 syn + anti CH3 X2 CH3 Carbocation H3C HBr, ROOR CH3 Alkyl halide X 2. HOOH, NaOH HO CH3 CH3 1. Hg(OAc )2, MeOH 2. NaBH4 H3 C CHX3, KOH CH3 X C OCH3 Ether 3-membered ring anti CH3 Cyclopropane None (concerted) syn N/A Cyclopropane None (concerted) syn N/A Alkane Heterogeneous syn N/A Epoxide None (concerted) syn N/A trans-1,2-diol 3-membered ring anti N/A trans-1,2-diol None (concerted) anti N/A X CH2I2, Zn(Cu) CH3 H C CH3 H H2, Pd/C CH3 (or H2, PtO2) CH3 RCO3H CH3 O CH3 H3O+, H2O O CH3 HO OH CH3 - OH, H2O O CH3 Markovnikov-like HO CH3 OH Cyclic (concerted) syn Cyclic (concerted) syn Cyclic (concerted) syn Aldehydes and Ketones Cyclic (concerted) syn CH3 Carboxylic acids and Ketones Cyclic (concerted) syn CH3 Carboxylic acids and Ketones Cyclic (concerted) syn 1. OsO4 CH3 2. NaHSO3, H2O (or H2O 2) HO CH3 OH HO CH3 OH KMnO4 (cold, dilute) - OH, H2O CH3 HO CH3 OH HIO4, H2O H CH3 cis-1,2-diol cis-1,2-diol Aldehydes and Ketones O O 1. O3 CH3 + 2. Zn(H3O ) or (CH3)2S 1. O3 CH3 H3O+, H2O CH3 O O HO 2. H2O2 KMnO4 (hot, conc'd) CH3 H O O HO O O