Reactions of Alkenes: Strategies and Mechanisms
The excerpt provides detailed insights into reactions of alkenes, emphasizing main reaction classes, key characteristics, intermediate states, and specific mechanisms like bridgehead halohydrin. It covers important concepts such as carbocation addition, free radical addition, and organometallic/redox reactions with examples and essential reaction conditions. Additionally, it discusses terms like anti-addition and Markovnikoff addition, highlighting the diverse pathways alkenes can undergo in chemical reactions.
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Presentation Transcript
Drill and practice with reactions of alkenes The 4 main classes of reactions of alkene are: (U-Pick) a) elimination, substitution, allylic addition, rearrangement b) SN1, SN2, E1 and E2 c) Carbocation addition, bridgehead addition, free radical addition and organometallic/redox reactions d) Radical substitution, SN1, E2 and allylic rearrangement In a carbocation addition, addition proceeds: a) To make rearranged alkene b) Anti-Markovnikoff, inverted c) Markovnikoff, inverted d) Markovnikoff, racemic Which class of reactions of alkenes always involves Br2 in CCl4 or ether ?Bridgehead (halohydrin) mechanism
Free radical additions are characterized by: a) Absence of peroxides and markovnikoff addition b) Formation of rings and unsaturated produces c) Presence of peroxides and markovnikoff substitution d) Presence of peroxides and anti-markovnikoff substitution Key intermediate state in halohydrin reactions : a) Sp2 Carbocation b) Free radical c) 3-atom semi-carbocation d) 5-coordinate complex Which reaction class(es) can produce larger dimers, trimers polymers d) carbocation c) radical a) bridgehead b) Organometallic /redox Which reaction class includes reactions that aren t additions ? Organometallic (ozonolysis and allylic substitutions)
Term Anti addition Reaction class Bridgehead (halohydrin) Anti Markovnikoff addition Radical addition Syn and anti; H.C. Brown, peroxy acids and NBS Organometallic/redox Dimers and trimers; industrial route to ethanol carbocation Polymerization; carbene insertion; freon additions Radical addition carbocation Markovnikoff addition
CCl4 wet OH + Br2 Br H+/reflux OH + H2O Hg(OAc)2 in THF NaBH4 /OH- OH >95% yield 100% Mark.
Product name ? OH OH cold KMnO4 Syn diol H peroxide, HBr in acetic acid Br peroxide/ light Etc
Br ethanol + KOH + major minor Run an ozonolysis O Zn/H+ O3 O Run the anti-Markovnikoff Brown 2 step preparation of alcohols H B2H6 neat H2O2 with OH- OH
ether Solvent ??? + H Br no peroxides H Br What s my common name ? CH2 uv light CH2 + + N N N N Cu diazomethane H Cl Cl + -+ Cl C Cl Cl H O
I ether Zn(Cu) + + CH2I2 + Zn I Organic halide Metal amalgam Simmons-Smith insertion What s my reaction name? Cl Cl Cl peroxide + C Cl Cl C Cl Cl Cl Pt, Pd, Rh, or Ni +H2
O H O H H H2O/H+ NaOH/H2O Wet CCl4 H + Br Br H OH An epoxide Anti-diol Industrial route to isopropanol ??? conc. H2SO4 H2O H O Besides cold KMnO4, what other reagent allows us to make a syn diol ? OsO4
Anti diol wet CCl4 H+ KOH + H O O Cl Cl OH Final product above is . Peroxide/formic acid (makes hydroperoxide) OH A different route to anti diol OH Starting from any alkene, make 3-bromo-1-butene in one step Br NBS light in ether
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