Post Prelim 3 and Final

ways to synthesize ethers
williams
alkoxy mercuration/reduction
(alcohol dehydration and alkene addition–not talk about in class-require strong acid and heat and 2 primary alcohols-symmetrical ethers, unsym ethers–3′, dilute strong acid)
williams
alcohol—– ether
alcohol + strong base (with THF) yields strong nuc and primary (or methyl) halide
Sn2 to create ether
-tertiary, secondary alkyl halides can not be used (formed)
alkoxy mercuration
alkene——ether
alkene (alcohol solvent) 1. Hg(OAc) (racemic) 2. NaBH4, HO- form racemic mixture
Ether reactivity
stable to strong bases and nuc
reactive to strong acids
Sn2, Sn1, E1
Epoxide synthesis
halohydrin cyclization
Direct epoxidation
direct epoxidation
(alkene oxidation by peracids)
peracid + benzene (any alkene)—-epoxide
concerted syn addition
5 arrows
Halohydrin cyclization
1. alkene + Br2 (in H20)
2. Base (H0- or pyridine)
ANTI (backside attack)
Epoxide reactivity
1. Grignard (-MgBr)
Sharpless Asymmetric Epoxidation
(uses +OOH, Ti (cat)) yield extremely selective eposide
Glycol Synthesis
1. epoxide hydrolysis
2. osmylation of alkenes
3. catalytic osmylation
epoxide hydrolysis
epoxide +H2O, H+ yield racemic glycol
osmylation of alkenes
OsO4 + alkene—osmate ester–)+H20—glycol (+detox)
concerted syn addition
catalytic osmylation
alkene + OsO4 + TMAO in pyrimidine and H20—glycol
glycol cleavage rxn
oxidation
Glycol + H5IO6—intermediate cyclic per-iodate ester—-aldehydes and ketones
nuc sub of epoxides under BASIC conditions
1. nuc sub
2. proton transfer
unsymmetric epoxides nuc react at least sub alkyl groups
inversion of config
nuc sub of epoxides under ACIDIC conditions
react with most sub alkyl group of epoxide 3′
2′,1′ give mixtures
inversion of configuration

if H20 is used as nuc product is glycol

IR
stretching and bending of bonds
E=
hv=(hc)/lambda
transmittance
emmergent/incident light
I/I0
3 principles of IR
1. bond stretching costs more E than bonding (higher f)
2. longer bonds (to heavier atoms) vibrate more easily than shorter bonds (to lighter atoms) (lower f)
3. single bonds vibrate more easily than multiple bonds (lower f)
IR limits
must be a change in dipole moment
symmetrical not see IR
Region 3600 cm-1 – 1600 cm-1 (left side of IR)
highest E
most stretching
diagnostic characteristic
1600cm-1- 600 cm-1 (right side of IR)
fingerprint region
electron impact ms
mw
m—m+ (parent ion) use m/z for mw—-fragmentation—- ch3+—ch2+
CIMS
gentler technique
M+ CH4+—H+—-[M-H]+ = CH3 radical
for a compound having n carbons in ms
n= (m+1)/m/(1.1)
if odd number of N atoms, molecular weight will be
odd
electrospray ionization
genetle
all parent ions present
spray mist of droplets, evap, gas phase ions
ms frag patterns: alkenes
parent ion even
frag odd
ms frag patterns: ethers
inductive cleavage, 2 pathways
ms frag patterns: alcohols and ethers: alpha cleavage
frag odd mass (even m/z m+)
ms frag patterns: primary alcohol 2 bond fragmentation
exception
even m+, EVEN mass fragment
NMR
nuc spin states
HextXhX gyromagnetic ratio
hv = resonant frequency
Hnet=
Hext + Hinduced + Hnearby nuc
Hnet
chemical shift Si (in ppm)=
(vi-vtms)/vinstrument
homotopic h
always same chem shift
enantiopopic h
same chem shift in achiral/racemic medium but may be different in chiral medium
diast h
may have different chem shifts in any medium
shielding
decreased local mag field by circulation of nearby e-
decreased e-neg–increased shielding
magnetic field of less shielded higher
As increase ppm
increase local field at protons
decrease shielding protons
increase proton chem shift
increase in chem shift due to (3)
increased e-neg
increased # e-neg groups
decreased distance of e-neg groups
when change in chemical shift is greater than J (constant)
n adjacent H give rise to n+1 multiplet
relative intensities are predicted by pascals triangle
J magnitude
Highest with H on same carbon (10-20 Hz)
and if double bond-trans
NMR can not detect…
alcohol, too rapid chem equil
13C NMR
fourier transform technique
-excite all 13C at once
-collect data (intensities over time)
-can transform data into intensities vs frequency
-Bc integrated peak areas are unreliable
-13C has a broad chem shift range
-watch for symmetry
alkynes
two pi bonds
good lewis bases
addition rxns alkynes
HBR
H20
Hydroboration oxidation rxn
addition rxns alkynes
HBR
H20
Hydroboration oxidation rxn
HBR + alkyne
2 -Br groups
H20 addition
with Hg+1, H2SO4
enol- ketone
acid (2 steps)
base (1 step)
If unsymmetric alkynes
give mixture of ketones
H20, hydroboration
Hydroboration oxidation of alkynes
disamyl borane
concerted cyn additon
antimarkovinikov
enol— aldeyhyde
alkyne reduction reactions
1. hydrogenation
2. lindars
3. Na metal in liquid NH3 reduction
alkyne hydrogenation
goes all the way to alkane
unless poisoned by Pb(OAc)2 and with CaCO3 (lindlars) to create CIS alkene only
Na Metal in liquid NH3 reduction of an akyne
yield TRANS alkene
Substitution reaction of alkynes
Need strong base
NaNH2, LDA, R-MgX
electrophiles:
alkyl halide
toluide

good for extending C networds

Tagged In :

Get help with your homework


image
Haven't found the Essay You Want? Get your custom essay sample For Only $13.90/page

Sarah from studyhippoHi there, would you like to get such a paper? How about receiving a customized one?

Check it out