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
explain cationic polymerization
acid (lewis or bronsted) + alkene –> C+
another alkene attacks C+
chain continues
conjugate base takes H+ from C+ and alkene forms at end of chain
explain radical polymerization
radical initiator: peroxide ROOR + heat/light –> 2RO-, homolytic cleavage
pi bond attacks radical, giving stabilized radical on C
Next pi bond attacks this radical and so on
chain terminates as an RO- attacks the C radical; RO ends up on both ends of chain
explain anionic polymerization
ester/nitrile (e- withdrawing group)
base catalyzed
anion attacks another substrate to give chain
super glue is an example of which kind of polymerization
anionic
“metathesis”
“change positions”
explain olefin metathesis
2 alkenes are cleaved and recombined
metathesis catalysts
Schrock & Grubbs
3 types of metathesis
1) cross metathesis
2) ring-closing metathesis
3) ring-opening metathesis
type of metathesis involved in polymerization
ring opening method
glycol
1,2-diol
how to form a Grignard?
RX + Mg in ether –> R-Mg-X
Grignard structure
RMgX
Grignard acts as a (C+/C-)
carbanion (Nu)
explain Grignard reaction
Grignard attacks backside of carbonyl
R of Grignard adds to carbon, giving (-) O
acid protonates O to give OH
Grignard rxn with acid chlorides and esters
2 equiv Grignard required
R adds twice
synthesis rxn for organolithiums
RX + 2 Li in Et2O, hexane, etc –> RLi
structure of organolithium
RLi
organolithium acts as (C+/C-)
carbanion
explain organolithium rxn
RLi attacks carbonyl
R attaches to carbon and carbonyl –> alcohol
explan organolithium rxn with acid chloride and ester
reacts twice just like Grignard
long name for Gilman reagent
Lithium dialkylcuprate
formation of Gilman rxn
R RLi + CuI –> R-CuLi-R
how is Gilman written
(R)2CuI
how to get from alkyl halide to Gilman reagent?
1) 2 Li
2) CuI
Gilman rxn with acid chlorides
R replaces X on starting material, giving Ketone, not alcohol
Gilman rxn with ester
none bitch!
Gilman reagents can undergo ____ reactions with alkyl halides
SN2
2 reagents for reduction of carbonyl & strength/use
NaBH4 – weak – ketones, aldehydes, acid chlorides
LAH – strong – ketones, aldehydes, acid chlorides, esters, carboxylic acids
explain hydride reduction of carbonyl
hydride attacks carbonyl
carbonyl becomes alcohol
if there is an acid chloride or an ester, that bitch gets kicked off and an alcohol is made (with LAH)
what is special about raney ni
reduces carbonyls, alkenes and alkynes in SM
6 methods of alcohol oxidation –> carbonyl
1) NaOCl + HOAc
2) NaOCl + TEMPO
3) Chromic acid (Jones reagent)
4) Pyridinium chlorochromate (PCC)
5) Swern oxidation
6) Dess-Martin Periodinate (DMP)
alcohol that cannot be oxidized
tertiary!!! bitch
TEMPO structure
what does TEMPO do to bleach
makes it a milk
VERY strong oxidizer of alcohols
Jones reagent (chromic acid)
2 ways to write Jones reagent (plus other condition in the stuff)
CrO3 + H2SO4
Na2Cr2O7 + H2SO4
3 methods of oxidizing alcohols that do the same damn thing
PCC
Swern
DMP
components of Swern reagent
- DMSO + (COCl)2 + -60°C
- Et3N
why is Swern better than PCC
less toxic for the environment and doesnt cause fucking CANCER like PCC does
DMP reagent structure
yeah memorize that. Bitch.
2° alcohol –> ketone oxidizing methods
6, all of them do this
1° alcohol –> aldehyde oxidizing methods
NaOCl + TEMPO
Swern
DMP
PCC
1° alcohol –> carboxylic acid oxidizing methods
NaOCl excess
Jones reagent
3 methods to convert alcohol to alkyl halide
1) HX method
2) PBr3 method
3) SOCl2 method
method to turn any ° alcohol into an alkyl halide
HX
can only turn 1° or 2 ° alcohol into alkyl halide
PBr3 or SOCl2
explain HX conversion of alcohol to alkyl halide
ROH + HX –> RX
if converting alcohol to alkyl chloride, use ______ reagent
ZnCl2
explain PBr3 rxn with alcohol
ROH + PBr3 –> RBr
inversion of stereochemistry!!
explain PBr3 rxn with alcohol
ROH + PBr3 –> RX
inversion of stereochemistry!!
explain SOCl2 rxn with alcohol
ROH + SOCl2 + pyridine –> RCl
inversion of stereochemistry IF you use pyridine!
formation of sulfonate ester rxn
ROH + TsCl + pyridine –> ROTs
alternatives to tosyl chloride
MsCl
TfCl
why is sulfonate ester reaction really useful
converts OH to OTs, and that’s a bitchin’ leaving group!
substitution or elimination y’all! it’s seriously cool
sulfonate ester rxn with NaOH gives…
an alcohol with a flipped stereochemistry (because SN2 backside attack)
sulfonate ester rxn with NaBr gives…
alkyl halide
sulfonate ester rxn with LAH gives…
alkane (basically taking off the alcohol altogther)
sulfonate ester rxn with NaOCH3 gives…
ether
what do you need for Williamson ether synth?
a 1° alkyl halide
an alcohol that’s been deprotonated
steps to williamson ether synth
1) deprotonate alcohol with strong base (NaOH, NaH)
2) add 1° alkyl halide
boom! you have an ether
how. tomake cyclic ethers???
intermolecular rxn with williamson ether synthesis —- alcohol on one end of a chain, alkyl halide on the other, they come together and smooch O
reagent used for cleavage of ethers
HX, excess
explain HX cleavage. ofethers
the ether is chopped in half at the oxygen. Where the oxygen was on each piece, there is now X
HX cleavage of ether mechanism
ether O attacks H on HX
X- attacks less sub. C+; alcohol leaves, giving product #1
alcohol attacks H on HX again
protonated alcohol leaves; X- attacks C+, giving product #2
2 methods to form epoxides
1) mCPBA (peroxyacid)
2) halohydrin + base
when forming an epoxide it replaces a(n)…
alkene
cis alkene + mCPBA –>
cis epoxide
trans alkene + mCPBA –>
trans epoxide
if we have 2 alkenes in a SM, and we use 1 equiv. mPBCA……
epoxide forms on the most sub. alkene
reagents used in halohydrin method of epoxide formation
- Br2 + H2O
- NaOH + H2O
steps in halohydrin/base formation of epoxide
1) halohydrin forms across alkene
2) base deprotonates OH, and O- attacks adjacent C (on itself!!), kicking off the Br and giving epoxide
epoxide rxns are the addition of a (Nu/El)
nucleophile
2 types of epoxide ring opening
acid-catalyzed
base-catalyzed
how to get trans diol from epoxide
cis epoxide + H3O+ –> trans diol (enantiomers)
difference between acid/base catalyzed ring opening of epoxides
acid: addition on the most sub. C
base: addition on the least sub C
how to add carbons, or H, to epoxide rings?
carbons – use Grignard
hydrogens – use LAH
pinacol
1,2-diol/glycol
reagent used in pinoacol–>pinacolone rxn
H2SO4 in water
pinacol –> pinacolone rxn
one OH attacks hydrogen on sulfuric acid
protonated alcohol leaves
methyl shift on C+; other OH makes double bond to C
OH is deprotonaed by water, giving ketone
