O2
O3
X2
H2O2
NaOCl
CrO3 or any Cr2
PCC
KMnO4
OsO4
Ag2O
HClO4
HIO4
Reducing Agents
H2
Li
Na
K
NaBH4
LiAlH4
Reduction of alkynes to trans alkenes
Na and liq. NH3 (sometimes with EtOH)
Two Hs added to opposite sides of alkene
Reduction of Alkynes to Cis alkenes
H2 and Lindlar's catalyst (Pd, quinoline, CaCO3, Pb(OAC)2)
Two Hs added to same side of alkene
Alkynes are more reactive than alkenes and Lindlar’s is too weak for alkenes
Reduction of alkenes to alkanes (Catalytic Hydrogenation)
H2 excess, catalyst (Ni, Pd, Pt, Pd/C)
Exothermic
Always syn addition of Hs
Reduction of alkynes to alkanes (Catalytic Hydrogenation)
H2 excess, catalyst (Ni, Pd, Pt)
4 Hs added
Stability of Alkenes
More substituted is more stable
Trans is more stable than cis
Reduction of alkyl halides to alkanes w/LAH
Also written LiAlH4
SN2 rxn
X is substituted with H
X = I > Br > Cl (not F)
Rate of rxn : Me > 1 > 2 (not 3)
Epoxidation of alkenes w/ Peracids
Alkene forms epoxide
Rxn is stereospecific (if it starts cis the epoxide ends in cis)
Weakest O-H bond from peroxide moves
1 step rxn no intermediate
Common peracids: MCPBA and MMPP
Oxidative Cleavage of Alkenes
O3
H2O, CH3SCH3, PPh3
Cut in half at alkene and add =O to make aldehyde or ketones
Oxidative cleavage of Alkynes (Ozonolysis)
O3
H2O, CH3SCH3, PPh3
Internal Alkyne: cut in half and make two carboxylic acids
Terminal Alkyne: cut in half and make carboxylic acid and CO2
PCC Oxidation (Pyridinium chlorochromate)
Soluble in organic solvent
Stops at aldehyde and doesn't go to COOH even with primary OH
O becomes double bonded and H attaches to C
Oxidation of Alcohols
Primary [O] aldehyde [O] carboxylic acid
Secondary [O] ketone
Tertiary [O] no rxn
[O] conditions:
Na2Cr2O7 or K2Cr2O7 over H2SO4, H2O
And H2CrO4 over acetone (jones reagent)
Anti - 1,2 - dihydroxylation
Peracid
H+ or OH- in H2O
OH added to opposite sides of C-C bond
First peracid makes an epoxide where R1 and R3 stay cis so dashed
Then second step opens ring with OH on straight bonds
If cyclo then racemic mixture of OH on dashed and wedged
Syn - 1,2 - dihydroxylation
3 conditions:
Cold KMnO4 over OH- and H2O
Cat OsO4, NMO 2) NaHSO3, H2O
OsO4 2) NaHSO3, H2O
OH added to straight bonds on same side of C-C bond
Needs to be rotated 180 for final product where OH is across from each other
Chapter 13
Breaking into radicals : homolytic cleavage and endothermic
Radicals are sp3, trigonal planar, 120, empty p-orbital
Most stable to least stable: 3 > 2 > 1 > methyl
Why? Hyperconjugation (R groups stabilize radical C)
Induction (electrons flow from sp3 C to sp2 C)
How do radicals react
Radicals attack sigma bonds: radical hits bond and takes H
Radicals attack pi bonds: radical hits bond and attaches to C
Radicals attack radicals: coupling exothermic
Alkanes w/ Halogens
Exothermic
R-H + X2 with light and heat makes R-X + HX
X2 is either Cl or Br
Alkane w/ Cl2
Initiation: Cl-Cl breaks to two Cl rad
Propagation:
Cl rad + alkane making Cl-H and alkane rad
Alkane rad + Cl-Cl making alkane with one less H and Cl attached
Chlorination of Higher Alkanes
Cl2 with light heat
# of signals is types of products
Not very regioselectivity
Bromination of Higher Alkanes
Br2 with light heat
Very regioselective Br goes to most sub C
Radical Stability
Allylic radical > 3 > 2 > 1 > me > vinyl =.
Stereochemistry of radical Halogen
Cl rad + alkane
Cl & Br can be added to top or bottom on straight bond creating enantiomers or diasteromers
Allylic Substitution
If it is alkene + X2 at high concentration, low temp over a non polar solvent then it is a vicinal dihalide ( X to both previous alkene Cs)
If it is alkene + X2 at low concentration, high temp then one X subs on sp3 C attached to double bond and the bond stays and HX is made
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