Post Prelim 3 and Final

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ways to synthesize ethers
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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)
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williams
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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)
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alkoxy mercuration
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alkene——ether
alkene (alcohol solvent) 1. Hg(OAc) (racemic) 2. NaBH4, HO- form racemic mixture
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Ether reactivity
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stable to strong bases and nuc
reactive to strong acids
Sn2, Sn1, E1
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Epoxide synthesis
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halohydrin cyclization
Direct epoxidation
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direct epoxidation
(alkene oxidation by peracids)
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peracid + benzene (any alkene)—-epoxide
concerted syn addition
5 arrows
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Halohydrin cyclization
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1. alkene + Br2 (in H20)
2. Base (H0- or pyridine)
ANTI (backside attack)
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Epoxide reactivity
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1. Grignard (-MgBr)
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Sharpless Asymmetric Epoxidation
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(uses +OOH, Ti (cat)) yield extremely selective eposide
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Glycol Synthesis
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1. epoxide hydrolysis
2. osmylation of alkenes
3. catalytic osmylation
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epoxide hydrolysis
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epoxide +H2O, H+ yield racemic glycol
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osmylation of alkenes
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OsO4 + alkene—osmate ester–)+H20—glycol (+detox)
concerted syn addition
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catalytic osmylation
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alkene + OsO4 + TMAO in pyrimidine and H20—glycol
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glycol cleavage rxn
oxidation
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Glycol + H5IO6—intermediate cyclic per-iodate ester—-aldehydes and ketones
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nuc sub of epoxides under BASIC conditions
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1. nuc sub
2. proton transfer
unsymmetric epoxides nuc react at least sub alkyl groups
inversion of config
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nuc sub of epoxides under ACIDIC conditions
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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

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

good for extending C networds

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