Building our Azobenzene Diacid

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Building our Azobenzene Diacid
EtONa, EtOH, Ether
KHCO3 EtOH I2 , reflux 84
KOH, Then HCL
Azobenzene Diacid
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Molecular Modeling
The phenylazobenzene chromophoric moiety is
expected to assume a roughly planar conformation
based on Hartree-Fock calculations
4 Å
Dihedral angle 179.92
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Molecular Modeling
The side chain is expected to be achiral due to
rapid inversion at the nitrogen.
Molecular modeling calculations confirm
achirality. (Note the hydrogen-bond.)
Hydrogen bond
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Proton Spectrum
Starting point Tentatively assigned to CH3
DMSO-d6 solvent peak
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Proton Spectrum-Broad Peaks
OH (possibly due to residual water) 3.8 ppm
Absorption peak observed around 12.7 ppm
suggests presence of COOH
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Proton Spectrum-Aromatic Region
Para Substituted azo/amine system expected to
have large chemical shift separation
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Proton Spectrum-Aromatic Region
Para Substituted azo/amine system expected to
have large chemical shift separation
Para Substituted azo/sulfonic acid system
expected to have smaller separation large
roofing effect
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ROESY- Pinpointing Aromatic Peaks
The multiple ROEs between the 6.8 ppm
Hydrogens and the rest of the molecule suggests
that these Hs are closest in space to the
aliphatic part (H-9 and H-13)
H-9, H-13
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Pinpointing Aromatic Peaks
By Process of elimination H-10 and H-12 may be
determined.
H-10, H-12
H-9, H-13
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HMQC- Aromatic Carbon Assignment
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HMQC Expansion- Aromatic Carbon Assignment
A/S
H-10, H-12
H-9, H-13
We can match the aromatic hydrogens to their
respective carbon systems--azo/amine
azo/sulfonic acid
C-9, C-13
A/S
C-10, C-12
A/S
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Carbon (13C) Spectrum- C-7 Assignment
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Carbon (13C) Spectrum- C-7 Assignment
Notice the peak adjacent to the large solvent
peak
DMSO-d6 Solvent
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HMQC- Methyl Carbon Assignment
C-7
H-7
H-10, H-12
H-9, H-13
A/S
We can tentatively assign C-7 based on HMQC
correlation
C-9, C-13
A/S
C-10, C-12
A/S
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HMBC- Tentative H-6 Assignment
H-10, H-12
H-9, H-13
H-7
H-6
A/S
Having identified C-7, we can ascertain the
identity of H-6 (since it is the only bound
proton expected to show long range heteronuclear
coupling to C-7)
C-7
C-9, C-13
A/S
C-10, C-12
A/S
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COSY- Linking the Aliphatic Chain
H-4
H-5
H-7
H-10, H-12
H-9, H-13
A/S
H-6
H-2
H-6 should only couple to one set of protons
(H-5) H-5 should couple to H-4 and H-6
protons H-4 should couple to H-5 and H-2
protons H-2 Should only Couple to H-4 SO FAR
SO GOOD!
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HMBC Spectrum- Further Confirmation for H
Assignments
H-2
H-7
H-6
H-10, H-12
H-9, H-13
A/S
H-4
H-5
The most deshielded carbon peak likely
represents the two COOH carbons We expect only
two hydrogens to show long range heteronuclear
coupling with the carbonyl carbons
C-7
C-9, C-13
A/S
C-10, C-12
A/S
C-1 C-3
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Proton Spectrum- Spitting Patterns and Chemical
Shift
Due to the ring inversion, we expect H-2 to be
a simple triplet (deshielded) H-6 and H-2 are
expected to exist at low field, while H-4 and H-5
will be at higher field Note Integrals give a
valuable estimate of proton numbers
H-4
H-5
H-2
H-6
H-7
1
3
2
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HMQC- Assigning the Remaining Carbon Peaks
C-4
H-10, H-12
H-9, H-13
H-2
H-6
H-4
H-5
H-7
C-5
A/S
C-7
C-2, C-6 ????
Schmeh!
C-9, C-13
A/S
C-10, C-12
A/S
C-1 C-3
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HMQC- Distinguishing the Signals of C-2 and C-6
C-6
C-2
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HMBC- Finishing Up Carbon Identification
H-2
H-10, H-12
H-9, H-13
H-6
H-4
H-5
H-7
A/S
Interesting long range coupling seems stronger
to meta carbon on the opposite side of the
benzene ring.
C-7
C-9, C-13
A/S
C-10, C-12
A/S
C-8
C-1 C-3
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Rationalizing the Upfield H Peaks
H-4
Gaussian Transform (LB -2, GB .3)
H-5
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ROESY-250- Future Directions
H-10, H-12
A/S
A/S
The possible existance of a ROE between the
inner Hs on the two benzene rings might allow
cis-trans isomerization or protonation studies.
H-10, H-12
??
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Future Directions
Choice of a different solvent might allow
separation of the aromatic peaks Decoupling
experiments would provide clues to the coupling
of the high field H peaks Protonation Study
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Concluding Evidence
Number of Carbons and Hydrogens match up to
spectral assignments Qualitative chemical
shift predictions are fulfilled All coupling
relationships can be rationalized. Reversing
the order of peak assignments leads to
inconsistent results Impurities likely exist
in sample
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