Unit 1 Flashcards
diastereotopic hydrogens
chemically nonequivalent and thus give different chemical shifts in NMR and typically occur in
1.) Chiral molecules (not considered in this course)
2.) Rings
3.) Double Bonds
more electronegative atoms have a () frequency
higher
aldehyde and carboxylic acid chemical shift
9-12 region
aromatic hydrogens
6.5 - 8 region
hydrogens on alkene
4.5 - 6.5 region
how do pi electrons shield protons
magnetic field is going in different directions
what percentage of hydrogens are in an alpha and beta state
50% alpha
50% beta
the alpha state is aligned with () and () in energy
magnetic field, lower
the beta state is aligned () and () in energy
against the magnetic field, higher
splitting when equivalent
(N+N+1)
splitting when nonequivalent
(N+1)(N+1)
what splitting pattern does a doublet of doublet result in
1:1:1:1
aryl
H’s on benzene
axial and equatorial hydrogens are chemically different - why do we only see 1 signal (as a singlet) for cyclohexane
chair conformer innerconversion
wet sample
the exchangeable H appears as a singlet and it no longer splits adjacent H signals
how many resonance structures does benzene have
2 equivalent
how many sp2 hybridized carbons does benzene have
6
what are the criteria for aromaticity
1.) cyclic
2.) planar
3.) continuous ring of p orbitals
4.) (4n+2) pi electrons –> odd number of electron pairs
anytime you see an Sp3, what can can you automatically classify the molecule as
nonaromatic –> not continuous loops of p orbitals
what hybridization is C+
sp2
what do you use to rank pKa
conjugate base of molecules
after 7 carbons in a ring, what happens to the shape
the ring often buckles and are no longer planar
non-aromatic compounds
do not fit the criteria for aromaticity
antiaromatic compounds
fit all the criteria for aromaticity except they have an even number of electron pairs
steps for ranking pKa
1.) draw conjugate base
(as pKa increases, acidity decreases)
2.) look at aromaticity to determine acidity
Most: aromatic
Least: antiaromatic
going downhill to lower energy is more/less feasable
more
Al, B, C+
all sp2
diene
recieves bond
dienophile
give bond
dine and dienophile combine to form what
2 new c-c bonds and a cyclohexane ring
molecular orbitals in diels alder
HOMO of diene overlaps with LUMO of dienophile
order of reactivity of diene molecules in a diels alder rxn
locked cis>trans>cis&trans>locked trans
1-substituted dienes produce what major product
ortho
2-substituted dienes produce what major product
para
diels alder stereochemistry
the stereochemical relationship of groups is retained from reactant to product
ex: groups that are cis on the dienophile are cis in the product
substitution with () on diene speed up the rate of reaction
EDG
substitution with () on dienophile speed up rate of rxn
EWG
