Post Prelim 3 and Final – Flashcards

Unlock all answers in this set

Unlock answers
question
ways to synthesize ethers
answer
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)
question
williams
answer
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)
question
alkoxy mercuration
answer
alkene------ether
alkene (alcohol solvent) 1. Hg(OAc) (racemic) 2. NaBH4, HO- form racemic mixture
question
Ether reactivity
answer
stable to strong bases and nuc
reactive to strong acids
Sn2, Sn1, E1
question
Epoxide synthesis
answer
halohydrin cyclization
Direct epoxidation
question
direct epoxidation
(alkene oxidation by peracids)
answer
peracid + benzene (any alkene)----epoxide
concerted syn addition
5 arrows
question
Halohydrin cyclization
answer
1. alkene + Br2 (in H20)
2. Base (H0- or pyridine)
ANTI (backside attack)
question
Epoxide reactivity
answer
1. Grignard (-MgBr)
question
Sharpless Asymmetric Epoxidation
answer
(uses +OOH, Ti (cat)) yield extremely selective eposide
question
Glycol Synthesis
answer
1. epoxide hydrolysis
2. osmylation of alkenes
3. catalytic osmylation
question
epoxide hydrolysis
answer
epoxide +H2O, H+ yield racemic glycol
question
osmylation of alkenes
answer
OsO4 + alkene---osmate ester--)+H20---glycol (+detox)
concerted syn addition
question
catalytic osmylation
answer
alkene + OsO4 + TMAO in pyrimidine and H20---glycol
question
glycol cleavage rxn
oxidation
answer
Glycol + H5IO6---intermediate cyclic per-iodate ester----aldehydes and ketones
question
nuc sub of epoxides under BASIC conditions
answer
1. nuc sub
2. proton transfer
unsymmetric epoxides nuc react at least sub alkyl groups
inversion of config
question
nuc sub of epoxides under ACIDIC conditions
answer
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
question
IR
answer
stretching and bending of bonds
question
E=
answer
hv=(hc)/lambda
question
transmittance
answer
emmergent/incident light
I/I0
question
3 principles of IR
answer
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)
question
IR limits
answer
must be a change in dipole moment
symmetrical not see IR
question
Region 3600 cm-1 - 1600 cm-1 (left side of IR)
answer
highest E
most stretching
diagnostic characteristic
question
1600cm-1- 600 cm-1 (right side of IR)
answer
fingerprint region
question
electron impact ms
answer
mw
m---m+ (parent ion) use m/z for mw----fragmentation---- ch3+---ch2+
question
CIMS
answer
gentler technique
M+ CH4+---H+----[M-H]+ = CH3 radical
question
for a compound having n carbons in ms
answer
n= (m+1)/m/(1.1)
question
if odd number of N atoms, molecular weight will be
answer
odd
question
electrospray ionization
answer
genetle
all parent ions present
spray mist of droplets, evap, gas phase ions
question
ms frag patterns: alkenes
answer
parent ion even
frag odd
question
ms frag patterns: ethers
answer
inductive cleavage, 2 pathways
question
ms frag patterns: alcohols and ethers: alpha cleavage
answer
frag odd mass (even m/z m+)
question
ms frag patterns: primary alcohol 2 bond fragmentation
answer
exception
even m+, EVEN mass fragment
question
NMR
answer
nuc spin states
HextXhX gyromagnetic ratio
hv = resonant frequency
question
Hnet=
answer
Hext + Hinduced + Hnearby nuc
Hnet<Hext
question
chemical shift Si (in ppm)=
answer
(vi-vtms)/vinstrument
question
homotopic h
answer
always same chem shift
question
enantiopopic h
answer
same chem shift in achiral/racemic medium but may be different in chiral medium
question
diast h
answer
may have different chem shifts in any medium
question
shielding
answer
decreased local mag field by circulation of nearby e-
decreased e-neg--increased shielding
magnetic field of less shielded higher
question
As increase ppm
answer
increase local field at protons
decrease shielding protons
increase proton chem shift
question
increase in chem shift due to (3)
answer
increased e-neg
increased # e-neg groups
decreased distance of e-neg groups
question
when change in chemical shift is greater than J (constant)
answer
n adjacent H give rise to n+1 multiplet
relative intensities are predicted by pascals triangle
question
J magnitude
answer
Highest with H on same carbon (10-20 Hz)
and if double bond-trans
question
NMR can not detect...
answer
alcohol, too rapid chem equil
question
13C NMR
answer
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
question
alkynes
answer
two pi bonds
good lewis bases
question
addition rxns alkynes
answer
HBR
H20
Hydroboration oxidation rxn
question
addition rxns alkynes
answer
HBR
H20
Hydroboration oxidation rxn
question
HBR + alkyne
answer
2 -Br groups
question
H20 addition
answer
with Hg+1, H2SO4
enol- ketone
acid (2 steps)
base (1 step)
question
If unsymmetric alkynes
answer
give mixture of ketones
H20, hydroboration
question
Hydroboration oxidation of alkynes
answer
disamyl borane
concerted cyn additon
antimarkovinikov
enol--- aldeyhyde
question
alkyne reduction reactions
answer
1. hydrogenation
2. lindars
3. Na metal in liquid NH3 reduction
question
alkyne hydrogenation
answer
goes all the way to alkane
unless poisoned by Pb(OAc)2 and with CaCO3 (lindlars) to create CIS alkene only
question
Na Metal in liquid NH3 reduction of an akyne
answer
yield TRANS alkene
question
Substitution reaction of alkynes
answer
Need strong base
NaNH2, LDA, R-MgX
electrophiles:
alkyl halide
toluide

good for extending C networds
Get an explanation on any task
Get unstuck with the help of our AI assistant in seconds
New