Exam 4 Flashcards
explain what is necessary for hydrogenation of alkenes/alkynes
H2
a catalyst
solvent
heat
pressure
2 equiv. if taking alkyne to alkane
hydrogenation is (reduction/oxidation)
reduction
heterogenous hydrogenation catalysts
Pd, Pt, Ni
Wilkinson’s catalyst:
- formula
- type of catalyst
Rh(PPH3)3Cl
homogeneous hydrogenation catalyst
homogeneous hydrogenation catalyst
Wilkinson’s
hydrogenation with a metal catalyst is (anti/syn)
syn
How to accomplish cis partial hydrogenation of alkyne?
Lindlar’s catalyst
P-2 catalyst
Lindlar’s catalyst:
- formula
- use
Pd/CaCO3 + quinoline
used to hydrogenate alkyne to cis alkene
P-2 catalyst:
- formula
- use
Ni2B
used to hydrogenate alkyne to cis alkene
How to accomplish trans partial hydrogenation of alkyne?
metal ammonia —Li, Na, or K + NH3 or RNH2
what is dissolving metal reduction?
partial hydrogenation of alkyne to give trans alkene
temp needed for dissolving metal reduction
cold
hydrogenation using radical mechanism
dissolving metal reduction; metal has one electron; attacks twice
sodium borohydride reduction —solvents
water
alcohol
ethers
LAH reduction —solvents you cannot use
water
alcohols
(reacts explosively)
carbene structure
carbene acts as (Nu/El)
either one!
3 methods of carbene addition
1) diazomethane
2) SImmons-Smith
3) Alpha elimination
Diazomethane reagent
diazomethane conditions required
heat or light
problems with diazomethane
very explosive & toxic
carbene can also insert into C-H bonds
Simmons-Smith reagent
ICH2ZnI
“figure 8” transition state
Simmons-Smith
Alpha elimination reagent
haloform (CHX3)
OH-
gives cyclopropane with 2 halogens
alpha elimination carbene addition
carbene adds to ___ bond
double
byproduct of diazomethane reaction
N2
explain syn 1,2-dihydroxylation
addition of 2 OH across C=C bond to give diol
2 methods of syn 1,2-dihydroxylation
1) KMnO4 + OH- + H2O + cold
2) OsO4 + pyridine; NaHSO3 + H2O
KMnO4 in COLD
syn 1,2-dihydroxylation
KMnO4 in HEAT
oxidative cleavage of alkenes
syn 1,2-dihydroxylation TS & relationship to stereochem of product
5-membered ring structure - must be cis - therefore product is trans
problems with KMnO4 method of syn 1,2-dihydroxylation
lower yield
byproducts due to overoxidation in any heat
problems with OsO4 method of syn 1,2-dihydroxylation
extremely toxic, but yield is higher
in the syn 1,2-dihydroxylation reaction, a trans alkene gives _________; a cis alkene gives _________
trans: 2 enantiomers
cis: meso
2 methods of oxidative cleavage of alkenes
1) KMnO4 + OH- + heat
2) ozonolysis
different types of alkenes & products with KMnO4 oxidative cleavage
unsubstituted: gives carbonyl product + CO2
monosubstituted: gives carboxylic acid (when tx with H3O+)
disubstituted: gives ketone
different types of alkenes & products with ozonolysis
unsubstituted: gives formaldehyde
monosubstituted: gives aldehyde
disubstituted: gives ketone
more useful reagent for oxidative alkene cleavage
ozone
name of ozonolysis mechanism
1,3-dipolar cycloaddition
ozonolysis conditions
anhydrous
difference between KMnO4 and ozonolysis in oxidative cleavage of alkynes
there is none!
internal alkyne gives 2 ___________ upon oxidative cleavage
carboxylic acids
alkyne + KMnO4 + heat + neutral conditions –>
diketone
diketone formation TS
tetrahydroxy
reagents used to turn alkene into an alkyne
X2
2 mol NaNH2
double dehydrohalogenation involved in…
synthesis of alkyne from alkene by elimination
steps in synthesis of alkyne from alkene
alkene + X2 –> vicinal dihalide
+ 2 mol NaNH2 –> alkyne + 2 NH3 + 2 NaX
steps in synthesis of acetylene
geminal dihalide + 3 mol NaNH2 –> acetylide ion
+ acid –> acetylene
used to deprotonate acetylene
NaNH2
3 methods of polymerization
1) cationic
2) radical
3) anionic (rare)
3 steps for any method of polymerization
1) chain initiation
2) chain propagation
3) chain termination