Addition Reactions of Alkenes and Alkynes

electrophile

electron seeking reagent; react with electrons in pi bond; BL and LA acids; proton donor/electron acceptor

order of reactivity of hydrogen halides

HI>HBr>HCl>HF

addition of hydrogen halide to alkene

Markovnikov, RDS step 1; 2 energy maximums; anti addition

Markovnikov's Rule

in the addition of HX to an alkene, the H atom adds to the carbon of the double bond that already has the greater number of hydrogen atoms

Markovnikov's Rule

in the ionic addition of an unsymmetrical reagent to a double bond, the positive portion of the adding reagent attaches itself to a C atom of the DB so as to yield the more stable carbocation as an intermediate

regioselective

reaction that can potentially yield 2 or more constitutional isomers and actually produces 1

anti-Markonikov

alkenes treated with HBr in presence of peroxides; H attaches to C with fewer H atoms; does not occur significantly with HF, HCl, HI

hydration

addition of water

acid-catalyzed hydration

Markovnikov addition; frequent rearrangements; dilute acid needed; lower temperature; H3O+/H2O; forms alcohols

oxymercuration-demercuration

Markovnikov addition; seldom rearrangements; room temp or below; gives high yields of alcohols; 1) Hg(OAc)2/THF-H2O; 2) NaBH4, OH-

solvomercuration-demercuration

solvent molecule acts as nucleophile in oxymercuration step; forms ethers; Hg(O2CC3)2/THF-ROH

hydroboration-oxidation

Anti-Markovnikov addition; syn addition of H and OH; seldom rearrangements; forms alcohols; BH3:THF; steric and electronic factors affect; B and H atom must add to same face of double bond

vicinal dihalides

form when alkenes react with Br or Cl in nonnucleophilic solvents; anti addition

trans -Br->

meso compound

cis -Br->

racemic mix of enantiomers

carbene

group of compounds in which C forms only 2 bonds; highly unstable; fleeting existence; simplest is methylene

methylene

simplest carbene; reacts with alkenes by adding to DB to form cyclopropanes

syn 1,2-dihydroxylation

synthesizes 1,2-diols (glocols); 1) OsO4, pyridine; 2) NaHSO3/H2O; syn addition of O atoms

oxidative cleavage

breaks double bond; KMnO4 for strong, O3 for mild

ozonolysis

cleavage with ozone; most useful method for cleaving alkenes; very cold solution of alkene; 1) O3, CH2Cl2, cold; 2) Me2S; each carbon of the DB becomes doubly bonded to an O atom

addition of HX to alkynes

2 molar eq; forms geminal dihalides; H atom attaches to C that has greater number of H atoms

oxidative cleavage of alkyes

with oxone/HOAc or KMnO4/H3O+; forms carboxylic acids RCO2H + R'CO2H