Final Flashcards
Electromagnetic radiation has properties of ?
particles and waves
product of frequency of wave and wavelength is?
speed of light
energy of each photon is ? to freq
proportional. E = hv
freq and wavelength are ?
inversely proportional
IR gives info about
functional groups
NMR gives info about
C-H chemical env
energy is not a continuum but exists at
discrete energy levels
energy diff between energy levels is
quantized
the molecule absorbs light when the phton has the energy that corresponds
exactly to delta E
functional groups are detected by Ir bc each bond type has a
characteristic delta E between vibrational states based on bond strength and length
Ir spec if a plot showing the
absorption of energy against freq of light
relationship between wave number and mass
lower mass = larger wavenumber or freq
higher mass = lower wavenumber or fre
relationship btwn bond strength and wavenumber
stronger the bond, the higher the force constant so the larger the wavenumber or freq
trend for wavenumbers in general from large to small
X-H then triple bonds then double bonds then single
relationship between wavenumber and hybridization
sp has higher then sp2 then sp3
relationship between wavenumber and ring strain
inc ring strain = larger wavenumber
relationship between wavenumber and conjugated systems
more resonance = lower wavenumber bc more single bond character
what 2 factors impact signal intensity
bond polarity and number of identical bonds present
relationship between dipole moment and signal intensity
more polar = stronger signal
relationship between number of identical bonds and signal intensity
more identical bonds = stronger signal
distribution of O-H bonds give rise to a
broad signal bc of H bonding
secondary amines have how many N-H signals?
1
primary amines have how many N-H signals?
2
mass spec is used to determine the ? of a molecule
molecular weight
e- impact ionization method uses a high energy e- which
strikes a vaporized molecule
Mass spec: energy rich molecule ejects an e- forming a + odd electron species called the
molecular ion (radical cation)
molecular ion passes btwn poles of a magnet and is deflected by the
magnetic field
Mass spec: which molecules get deflected more, smaller or larger?
smaller
intensity of peak is proportional to
percentage of each ion of diff mass in the sample
what is the molecular ion
molecular mass of the molecule minus an e-
what is the base peak
most abundant peak - 100% relative intensity
might not be the molecular ion peak
if base peak = molecular ion peak, then
no fragmentation occurred
what is the (M+1)+. peak
measures C-13
inc intensity w inc number of C
Characteristic ratio for Br on (M+2) peak
1:1
characteristic ratio for cl on (M+2) peak
3:1
NMr involves interaction btwn
EM radiation and nuclei of atoms
nuclei with odd number of protons have an intrinsic
nuclear spin
the nuclear spin creates a
small magnetic moment around the atom
nuclear spins are normally at ? but are aligned by a ?
random orientations, strong external magnetic field
spin state alpha
aligned w magnetic field, lower energy
spin state beta
against magnetic field, higher energy
when Em radiation is applied, nucleus in alpha spin state
absorbs energy of photon and flips to beta state
the difference in energy between alpha and beta spin states
is small and dependent on B0.
inc external magnetic field to
inc delta E between alpha and beta spin states
if a given nuclei has lots of e density, overall affect of b0 is weakened and the nuclei is said to be
shielded
if the nuclei has little e density, the nuceli is more affected by B0 and is
deshielded
downfield =
deshielded = less e- density = feels B0 more
upfield =
shielded = high e- density = feels B0 less
the main contributor to deshielding of vinylic and aryl protons is the induced magnetic field associated with pi electrons. what is this called
anisotropy
does anisotropy reinforce or oppose B0
reinforces
the intensity(not height, but area under signal) of NMR peak is dependent on
the number of chem equiv hydrogens giving rise to that signal
protons on adgacent carbons will interact and split eash other’s singles into
mulitplets
chemical shift of a proton is affected by
magnetic moment of adjacent protons
what is a J value
distance btwn peaks of a split pattern
protons coupled to each other have the same
J value
when does complex splitting occur
when neighbors are not chem equiv.
trans Hs on an alkene has ? J value than cis protons
higher
if OH signal is present in NMR, it is a
bs betweem 0.5 and 5
Does CNMR have spin-spin splitting
no
what does CNMR tell u
ho wmany diff carbon types there are
isolated dienes have
at least 1 sp3C between the alkenes
the single bond beteen 2 conjugated alkenes is relatively
short
there is max orbital overlap and e- delocalization on a conjugated diene if the 2 pi bonds are
coplanar
the two coplanar forms of a conjugated diene are
s-trans and s-cis
for MO diagrams, number of sp2 C
= number of p orbitals and psi`
traits of pericyclic rxns
e- move in loop, aromatic-like TS, concerted
electrocyclic rxns must be
fully conjugated polyene undergoes ring closure
sigmatropic rearrangements
2 db not conjugated
one sigma bond broken, one formed
diels alder rxn
cycloaddition rxn of diene and alkene
alkene is a dienophile
ex of pericylic rxn
4+2 cycloaddition
mediated by heat
the diene must be in the
s-cis conformation to react
cis to diene–>endo–>
anti
trans to diene–>exo–>
syn
endo approach is favored bc of
orbital stabilization of hte TS
endo product has subst. pointing ? relative to longest bridge
down
symmetry allowed
Homo of diene matches with lumo of dienophile
photochemical rxn
promotes HOMO, LUMO stays the same
cope rearrangement
all C
claisen rearrangement
allyl vinyl ethers
favors ketone until a benzene is present
define aromaticity
special stability due to resonance delocalizationm of the pi e- in a cyclic conjugated system/cmpd
huckel’s rule
planar
cyclic
fully conjugated
4n+2 e-
to be aromatic
to be antiaromatic must be
planar
cyclic
fully conjugated
4pi e-
in a frost circle, to be antiaromatic …
singly occupied MO or antibonding MO occupied
benzylic halides react faster than primary and allylic halides bc of
TS stabilization by orbital mixing
In EAS, what acts as the nuc
benzene
what is the intermediatea called for the EAS rxns
cyclohexadienyl cation, or arenium ion or sigma complex
limitations to friedel crafts alkylation
only alkyl halides ccan reaact
benzene can’t have strong EWG (NO2, CN, SO3H, ketones, aldehydes, CA, amides)
anilines do not undergo FCA- must protect with acyl chloride nd pyr
benefits of FC acylation
no ccat. rearrangement
if a subst. for EAS is activating, the rxn goes
faster
halogens are weak deactivators but are
o/p directing
aromatics more deactivated than a monohalobenzene cannot be
acylated or alkylated with FC. Add acyl gruop first
requirements for SNAR
LG, EWG O/P to each other
Benzene is e-phile
what is the intermediate for SNAR called
Meissenheimer called
the rate of SNAR inc w
-inc numbet of EWG
-what LG it is (F>Cl>Br>I)
Elimination addition requirements
LG
intermediate for elimination addition rxn
benzyne
nuc attack at a carbonyl happens at what orbital
pi*
when do imines form
primary amine + carbonyl
when do enamines form
secondary amine + carbonyl
thioacetals have an acidic proton that can be deprotonated with
nBuLi
what is a ylide
dipolar intermediate with opposite formal charges on adjacent atoms
wittig reaction is highly selective for
ketones and aldehydes
what will not react but are tolerated in a rxn with wittigs
esters, lactones, nitriles, amides
what are not tolerated at all with wittigs
acidic groups (alc, amine, CA)
wittig reagents from simple alkyl halides form the
Z alkene (kinetic product)
wittig reagents with adhacent carbonyls form the
E alkene (thermo product)
baeyer-villiger oxidation priority
H>3>2, Ph>1>methyl
grignards react with?
acidic H–> protect free OHs
what reagent selectively reduces CA in the presence of other carbonyls
BH3THF
stabilization of carbonyls depend on
resonance
most reactive CA derivation to least
acyl chloride, anhydrides, esters, amides
what reagent do u use to get single addition of a c nuc to an acyl chloride
gilman
addition of grignard to nitriles gives an
iminium
iminium is hydrolyzed to
ketone
how many equivalents of grignards is added to nitriles
1
keto form is most common, but ? is the reactive species
enol
enol form of carbonyl contributes to reactivity at
alpha c
2 reasons for inc acidity of carbonyls relative to alkanes
1- induction from O
2- after deprotonation, (-) of enolate ion is stabilized by resonance
are enols or enolates more reactive
enolates
what is an aldol addition
addition of one enolate of a carbonyl with a second carbonyl
what is the product of aldol condensation
alpha beta unsaturated ketone/aldehyde
what happens when aldol addition is under heat and acid
aldol condensation
what base to use for directed aldol addition
LDA
what is a claisen condensation rxn
enolate of one ester reacts w a second ester
the alkoxide that is used as a base is the same as the ester group to avoid
trans-esterification
what is dieckmann cyclization
intramolecular claisen condensation
for unsymmetric ketones, use LDA, THF, -78 for
least sterically hindered deprotonation
kinetic product
for unsymmetric ketones, use -OMe, MeOH
for subst. enolate
thermo product
the thermo enolate us formed under ? conditions
reversible, with alkoxide base in protic solvent and rt
kinetic enolate is formed by ? conditions
irreversible, with SB, aprotic solvent and cold
alpha, beta unsaturated ketones and aldehydes are prepared by
- aldol rxns with dehydration of aldol
- alpha halogenation of ketone or aldehyde followed by elimiation
strong basic nucs react at the carbonyl carbon
Grignards and LAH
kinetic favored
less basic nucs react at beta carbom
enolates, gilman, amines, thiolates, cyanide
therm0 favored
what is michael addition
conjugate addition of an enolate to alpha, beta unsaturated ketone
what is robinson annulation
michael addition followed by intramolecular aldol condensation
what is the LG in hoffman elimination
quaternary amine
hoffman elimiation gives what product
least subst. alkene
what is the LG for nitrosation of alkylamines for secondary and tertiary amines
diazonium cation
at C1 of an aldose, the carbonyl is an
aldehyde
if there is a ketone anywhere else besides C1, it is a
ketose
carbs are desugbated as D or L according to the sterochem of the highest numbered
chiral carbon of fischer
what are the 4 stereoisomers of the aldotetroses
D and L erythrose, D and L threose
stereoisomers of aldopentoses
ribose (all right), arabinose is only top. xylose is middle and lyxose is top 2
pneumonic for aldohexoses
all altruists gladly make gum in gallon tanks
numbers for aldohexoses
1 2 1,2, 3 1,3 2,3 1,2,3
aldohexoses
allose altrose glucose mannose gulose idose galactose talose
aldoses contain a ? and ? which react to form cyclic ?
aldehyde, alcohols, hemiacetals
define anomers
carb isomers that differ only in stereochem of anomeric carbon
subst that are right on the Fischer point ? and those on the left point ?
down, up
to go from fischer to pyranose
manipulate so last OH is vertical
what is mutarotation
alpha and beta anomers are in equilibrium and interconvert via open form when react w water
anomeric carbon of pyranose and furanose form of ketose has both a
OH and CH2OH
the anomeric effect stabilizes an EN subst. on the anomeric carbon by
orbital mixing
the axial subst. is stabilized by interaction of a non-bonding e= pair on the ring O with the sigma star orbital which
lowers the energy of the overall molecule
the EN group prefers to be
axial
glycoside formation
anomeric OH is replaced by some other subst.
in fischer glycosidation carbs react with
an alc in the presence of an acid catalyst
fischer glycosidation is thermo controlled and favors formation of
pyranose over furanose
anomeric effect causes ? stereoisomer to predominate over ?
alpha over beta
the glycosol donor…
has a LG and is the e-phile
the glycosol acceptor….
has one free OH and is the nuc
in deoxy sugars a OH group is replaced with
H
amino sugars have an amino group in place of a
OH
amino acids are
amphoteric
what is the pI
pH at which the aa exists largely in a neutral form
when pH < pI
aa is +
when pH > pI
aa is -
the amino group can be protected using
BOC (deprotect w TFA) or FMOC (deprotect w piperidine)
the c terminus is protected using
benzyl bromide (deprotect with H2, Pt)
why use DCC
activates COOH to accelerate amide bond formation
