Orgo I: Chapter 8: Alkenes: Reactions and Synthesis

How are alkenes usually prepared

Elimination forming alkene and X-Y

dehydrohalogenation

loss of HX from alkyl halide usually by reaction of an alkyl halide with a strong base like potassium hydroxide

dehydration

loss of water from an alcohol, treatment of an alcohol with a strong acid, in tetrahydrofuran (THF)

halogenation

rapid addition of halogens to alkenes to yield 1,2-dihalides (Br & Cl)

bromonium ion

Intermediate formed during bromination of alkenes. R2Br+

why is trans product formed for halogenation

when the bromonium ion forms, the bromine acts as a shield to one side making the second bromide attach at the opposite side

halohydrin reaction

C=C —> (NBS/DMSO) bromonium ion, h2o added, Br-C-C-OH2+ second h2o forms hydronium leaving halohydrin Br-C-C-OH

What are the usual solvents and reagents for bromohydrin formation?

CH3SOCH3 (DMSO) solvent, N-bromosuccinimide (NBS) reagent is the source of Br2

hydration

C=C —> (H3O+) double bond donates to H, H donates to O +C-C-H —>(H2O) +OH2-C-C-H —> (H2O) O donates to H H donates to O HO-C-C-H + H3O+ (markovnikov)

oxymercuration-demercuration reaction

C=C —> (Hg(OAc)2) Mercurinium ion (HgOAc+) —> (H2O) HO-C-C-HgOAc —> (NaBH4) HO-C-C-H (markovnikov)

hydroboration is the alternative to?

complementary method to oxymercuration-demercuration that produces a non-markonikov alcohol

what are the intermediates in hydroboration?

C=C —> (BH3/THF) --> organoborane intermediate H-C-C-BH2 —> (H2O2/ OH-) --> H-C-C-OH (non-markovnikov’s alcohol)

syn stereochemistry

addition to the same side of the double or triple bond

hydrogenation

C=C —> (H2, PtO2/CH3O2H) H3-C-C-H3 (cis)

epoxide

oxirane, cyclic ether with an oxygen atom in a 3 membered ring

epoxidation reaction

C=C —> (H-O-O-(C=O)-R) Epoxide + H-O-(C=O)

diol formation via epoxide

C=C —> (H-O-O-(C=O)-R) Epoxide (+ H-O-(C=O)) —> (H3O+) Epoxide-H+ —> (H2O) HO-C-C-OH2+ —> HO-C-C-OH (trans)

diol formation with only one intermediate

C=C —> (OsO4) cyclic osmate intermediate —> (NaHSO3/H2O) HO-C-C-OH (cis)

ozonolysis reaction

C=C —> (O3/CH3Cl2) molozonide (clockwise, -O-O-O-C-C-) —> ozonide (clockwise, -O-O-C-O-C-) —> (Zn/CH3CO2H/H2O) C=O C=O

what will potassium manganate produce and how

carboxylic acids and CO2 if H are present H3C-C=C-H2 —> (KMnO4/H3O+) H2C-(C=O)-OH + CO2

HIO4 reaction

simplest way to generate a carbene

treat CHCl3 with strong base like KOH

is the product of the reaction between dichlorocarbene and alkene stereospecific

yes cis with cis and trans with trans