Identification and quantification of cis and trans isomers in aminophenyl double-decker silsesquioxanes using 1H-29Si gHMBC NMR

Article abstract of DOI:10.1002/mrc.3962

Cis and trans isomers of a series of double-decker silsesquioxanes (DDSQ) were characterized by two-dimensional NMR techniques. The ¹H NMR spectra of these species have not previously been assigned to a degree that allows for quantification. Thus, ¹H-²⁹Si HMBC correlations were applied to facilitate ¹H spectral assignment and also to confirm previous ²⁹Si assignments for this class of silsesquioxanes. With the ability to identify all the pertinent resonances of the ¹H NMR spectrum, ²⁹Si NMR is no longer required for quantification and required only for characterization. This not only saves time and material but also provides a more accurate quantification, thus allowing for the ratio of cis and trans isomers present in each compound to be determined. A more accurate measure of the cis/trans ratio enables the investigation of its influence on the physical and chemical properties of DDSQ nanostructured materials. Copyright

Full text of DOI:10.1002/mrc.3962

MRC Letters
Received: 1 March 2013
Revised: 5 April 2013
Accepted: 8 April 2013
Published online in Wiley Online Library: 27 May 2013
(wileyonlinelibrary.com) DOI 10.1002/mrc.3962
Identification and quantification of cis and
trans isomers in aminophenyl double-decker
1
silsesquioxanes using H–29Si gHMBC NMR
B.W. Schoen,a D. Holmesb and A. Leea*
Cis and trans isomers of a series of double-decker silsesquioxanes (DDSQ) were characterized by two-dimensional NMR
techniques. The 1H NMR spectra of these species have not previously been assigned to a degree that allows for quantification.
Thus, 1H–29Si HMBC correlations were applied to facilitate 1H spectral assignment and also to confirm previous 29Si
assignments for this class of silsesquioxanes. With the ability to identify all the pertinent resonances of the 1H NMR spectrum,
29Si NMR is no longer required for quantification and required only for characterization. This not only saves time and material
but also provides a more accurate quantification, thus allowing for the ratio of cis and trans isomers present in each compound
to be determined. A more accurate measure of the cis/trans ratio enables the investigation of its influence on the physical and
chemical properties of DDSQ nanostructured materials. Copyright © 2013 John Wiley & Sons, Ltd.
1
Keywords: NMR; H; 29Si; 2D NMR; 1H–29Si HMBC; double-decker silsesquioxanes; cis/trans isomers
cyclohexylsilyl]-bridged-(phenyl)8-double-decker silsesquioxane,
DDSQ(m-AP)(Cy), are assigned, and their ratios are quantified. In
Introduction
Inorganic–organic nanostructured molecules combine the
thermostability of inorganics with the chemical flexibility of
organics, thereby providing a versatile platform that has attracted
attention over the last two decades.[1–11] A recently developed
platform known as double-decker silsesquioxanes (DDSQ) (e.g. 3)
provides a unique opportunity to investigate the influence
of stereo-configurations on the physical and chemical properties
of silsesquioxanes. DDSQ are composed of two ‘decks’ of
silsesquioxanes stacked on top of one another forming a cage-
like structure.[12–19] Typically, the DDSQ (3) are synthesized through
reacting a dichlorosilane with a tetrasilanol (2a) which generates
both cis and trans isomers. DDSQ with various chemical moieties,
including aminophenyls, and 2-methylpropyl-hydroxyl have been
synthesized, and their cis and trans isomers have been partially
isolated.[14,15] These isomers have been identified using one-
dimensional (1D) 29Si NMR spectroscopy.[14–19] While 29Si NMR does
benefit from large chemical shift dispersion typically leading to
reduced spectral congestion, the technique is not ideal.[20] 29Si
NMR delivers lower relative sensitivity when compared to that of
1H NMR; it also requires a longer recycle delay and experimental
time for quantitative measurements, more concentrated samples,
and a broadband probe with appropriate hardware (i.e. broadband
amplifier, RF filters, and specific capacitor sticks for tuning) for accu-
rate results. These factors make 29Si NMR less desirable when com-
pared to the high sensitivity, shorter relaxation and acquisition
times, more dilute samples, and standard NMR equipment required
for 1H NMR. The ability to identify the isomeric ratio of DDSQ
molecules using 1H NMR spectroscopy would save time and
material and ultimately provide a more accurate quantification of
the isomeric ratio than utilizing 29Si NMR spectroscopy. In this
order to unambiguously assign the proton resonances and use
them for quantitation, two-dimensional (2D) NMR techniques were
necessary. Specifically, proton correlations to the silicon nuclei of
the silsesquioxane core not only facilitated 1H spectral assignment
but also confirmed previous 29Si assignments for this class of DDSQ.
Results and Discussion
DDSQ(m/p-AP)(Me) and DDSQ(m-AP)(Cy) were synthesized
according to a previously described method (Scheme 1, Fig. 1)
and produced a nearly equivalent mixture of cis and trans
isomers.[15] The isomeric mixture of each compound was
1
assessed by 29Si and H NMR, and diagnostic chemical shifts for
each isomer were observed in the spectra.[15] The isomeric mix-
ture of DDSQ(m-AP)(Me) (3a) shows the expected 29Si resonances
at d –30.6, –78.4, –79.4, –79.6, and –79.8 in a ratio of 2:4:1:2:1
(Fig. 2a). Trans DDSQ(m-AP)(Me) (trans 3a) shows characteristic
29Si resonances at d –30.6, –78.4, and –79.6 in the ratio of 2:4:4
(Fig. 2b), and cis DDSQ(m-AP)(Me)-isomer (cis 3a) has 29Si
resonances at d –30.6, –78.4, –79.4, and –79.8 in a ratio of 2:4:2:2
(Fig. 2c).[15] The 29Si resonance at d –30.6 has been assigned to
the D-group silicon atoms (Si-3), silicon atoms bonded to two
oxygen atoms (Fig. 1).[21] The 29Si resonance at d –78.4 has been
*
Correspondence to: A. Lee, Chemical Engineering and Materials Science, Michigan
State University, East Lansing, MI 48824, United States. E-mail: leea@egr.msu.edu
a Chemical Engineering and Materials Science, Michigan State University,
East Lansing, MI, United States
1
work, the H NMR spectra of cis and trans isomers of [(meta- and
para-aminophenyl)methylsilyl]-bridged-(phenyl)8-double-decker
silsesquioxane, DDSQ(m/p-AP)(Me), and [(meta-aminophenyl)
b Chemistry, Michigan State University, East Lansing, MI, United States
Magn. Reson. Chem. 2013, 51, 490–496
Copyright © 2013 John Wiley & Sons, Ltd.

Quantification of cis and trans isomers in double-decker silsesquioxanes
Scheme 1. Synthesis of DDSQ(m/p-AP)(R); X = Cl, Br; R = Me, Cy.
Figure 1. (a) cis/trans 3a: DDSQ(m-AP)(Me), (b) cis/trans 3b: DDSQ(m-AP)(Cy), and (c) cis/trans 3c: DDSQ(pAn)(Me).
assigned to the T-group silicon atoms, silicon atoms bonded to
three oxygen atoms, nearest to the D-group silicon atoms (Si-2).
29Si resonances at d –79.4, –79.6, and –79.8 have been assigned
to the internal T-group silicon atoms, Si-1cR, Si-1t, and Si-1cL,
respectively. Each Si-1t has the same chemical environment with
proximity to one methyl and one aminophenyl group, giving rise
to a single silicon resonance. In contrast, Si-1cR atoms are only
proximal to the methyl group and Si-1cL to the aminophenyl
group, thereby leading to two resonances. The 29Si resonances
for DDSQ(m-AP)(Cy) (3b) and DDSQ(p-AP)(Me) (3c) are nearly
identical: d –34.1, –78.5, –79.32, –79.5, and –79.7 (Fig. 2d), and
d –29.7, –78.2, –79.1, –79.3, and –79.5 in the ratio of 2:4:1:2:1
(Fig. 2e), respectively.
isomers. First, the proton signals belonging to the cyclohexyl
groups are broad, significantly overlapped, and have complicated
coupling patterns for cis and trans isomers. The proton signals
belonging to the methyl groups of each isomer are broad singlets
and overlap, making it difficult to integrate the individual peaks
in this region. Secondly, the 29Si signals associated with both
organic R-groups (Me and Cy), as evidenced by 1H–29Si
gradient-enhanced HMBC (gHMBC) cross-peaks, are isochronous
for cis and trans isomers. This makes it impossible to use the
previously established 29Si shift assignments to determine the
cis and trans proton signals in these regions, even if the signals
were deconvoluted.
The 1H NMR spectra for these DDSQ derivatives reveal that the
proton resonances in the phenyl region (6.5–8 ppm) are the best
candidates for the quantitation of isomeric ratios (Fig. 3). Proton
signals belonging to the R-substituents (Me or Cy) proved to be
ambiguous when attempting to decipher between cis and trans
Compound 3a
The proton resonance at dH 7.54 was assigned to H-2a and H-2a0
(m, 16H) based on the gHMBC three-bond correlation with the
29Si single resonance at dSi –78.4 (Si-2), which is isochronous for
Magn. Reson. Chem. 2013, 51, 490–496
Copyright © 2013 John Wiley & Sons, Ltd.
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B. W. Schoen, D. Holmes and A. Lee
Figure 2. 29Si NMR spectra of (a) cis/trans 3a, (b) majority trans 3a, (c) majority cis 3a, (d) cis/trans 3b, and (e) cis/trans 3c.
1
both cis and trans isomers (Fig. 4a). Whereas the trans isomer
exhibits a single resonance for Si-1t (dSi –79.6), the cis isomer, due
to its asymmetry, has two pairs of Si-1 atoms, labeled Si-1cL (left)
and Si-1cR (right) (dSi –79.4 and –79.8 in a ratio of 2:2). The proton
multiplet at dH 7.48 was assigned to H-1acR and H-1acR´ (cis, m,
4H) as evidenced by the gHMBC correlation with the two Si-1cR
atoms (dSi –79.8). The proton multiplet at dH 7.16 was also assigned
to H-1acL and H-1acL´ (cis, m, 4H) based on the gHMBC correlation
with the two Si-1cL atoms (dSi –79.4). For the trans isomers, the
proton multiplet at dH 7.32 was assigned to H-1at and H-1at´
(trans, m, 8H), which is confirmed by the gHMBC correlation with
the Si-1t atoms (dSi –79.6). Both the cis and trans isomers show
isochronous resonances at dH 6.92 and 7.03 and were assigned to
H-3a and H-3e (m, 4H and m, 4H) based on the gHMBC
correlation with the four Si-3 atoms (dSi –30.5). Analysis of the
1H–1H gradient-enhanced COSY (gCOSY) spectrum revealed
that proton signals at dH 6.67 and 7.08 show correlations with dH
6.92 and 7.03, thereby establishing their assignment as H-3b
and H-3d. Proton multiplets assigned to H-1acL and H-1acL´
(dH 7.16) and H-1at and H-1at´ (dH 7.32) exhibit too much
overlap for accurate quantification. Thus, the proton resonances
assigned to H-1acR and H-1acR´ (dH 7.48) and H-2a and H-2a0
(dH 7.54) are the best candidates for quantification. An equivalent
ratio of the cis to trans isomers would therefore be represented by
a ratio of 1:4 for these resonances. The remaining protons were
identified by 1H–1H gCOSY cross-peaks and coupling patterns
(Table 1a).
Additionally, the 2D H–29Si gHMBC is analogous to that of 3a
(Fig. 3d)
Compound 3c
Similar to compounds 3a and 3b, the proton resonance at dH 7.55
was assigned to H-2a and H-2a0 (m, 16H) based on the correlation
with the 29Si single resonance at dSi –78.2 (Si-2), isochronous
for both cis and trans isomers (Fig. 4b). The proton multiplet at
dH 7.50 was assigned to H-1acR and H-1acR´ (cis, m, 4H),
as evidenced by the gHMBC correlation with the Si-1cR atoms
(dSi –79.5). The proton multiplet at dH 7.19 was also assigned to
H-1acL and H-1acL´ (cis, m, 4H) based on the gHMBC correlation
with the other two Si-1cL atoms (dSi –79.1). For the trans isomers,
the proton multiplet at dH 7.33 was assigned to H-1at and H-1at´
(trans , m, 8H) based on the gHMBC correlation with the Si-1t
atoms (dSi –79.3). The proton multiplet at dH 6.53 (8H) was assigned
to H-3a and H-3a´, as evidenced by the gHMBC correlation with the
four Si-3 atoms, and is isochronous for cis and trans isomers. The
assignment of H-3a and H-3a´ is unique to the para-structure (3c).
All 8 H-3 protons that demonstrate a three-bond gHMBC correlation
with the Si-3 atoms of 3c (H-3a and H-3a´) are represented by a
single multiplet. The same 8H-3 protons of the meta-species
(3a and 3b) are represented by two multiplets (H-3a, 4H and H-3e,
4H), due to the asymmetry inherent to the meta-structure. Analysis
of the 1H–1H gCOSY spectrum reveals that proton signal at dH 6.53
shows correlations with dH 7.47 (H-3b and H-3b´; isochronous for
cis and trans, m, 8H). However, also contrary to the 1H NMR spectra
of the meta-species, the proton multiplet assigned to H-3b and
H-3b´ (dH 7.47) overlaps the proton multiplet assigned to H-1acR
and H-1acR´ (dH 7.50), which was used for quantification of the iso-
meric ratio of the previous two compounds. Similar to compounds
Compound 3b
The 1H and 29Si NMR spectra of 3b show an analogous coupling
pattern to that of 3a with only a slight variation of chemical shifts.
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Magn. Reson. Chem. 2013, 51, 490–496

Quantification of cis and trans isomers in double-decker silsesquioxanes
Figure 3. 1H NMR spectrum of (a) cis/trans 3a, (b) majority trans 3a, (c) majority cis 3a, (d) cis/trans 3b, (e) cis/trans 3c, (f) majority trans 3c, and
(g) majority cis 3c.
3a and 3b, the proton multiplets assigned to H-1acL and H-1acL´ (dH
7.19) and H-1act and H-1act´ (dH 7.33) exhibit too much over-
lap for accurate quantification, and to a much larger extent
than the overlap of proton multiplets assigned to H-3b and
H-3b´ (dH 7.47) and H-1acR and H-1acR´ (dH 7.50) (Fig. 3).
Thus, the proton resonances assigned to H-2a and H-2a0 (dH
7.55) and H-1acR and H-1acR´ (dH 7.50), combined with H-3b
and H-3b´ (dH 7.47), are still the best candidates for quantifi-
cation. An equivalent ratio of the cis to trans isomers is repre-
sented by the proton signals at dH 7.50 and 7.47
integrating to 12H and the proton signal at dH 7.55 integrat-
ing to 16H, a ratio of 3:4. As the ratio of these signals in-
creases, the ratio of isomers in the sample becomes majority
cis 3c (Figs 3e–3g). A ratio of 1:2 would signify an isolated
trans 3c. The remaining protons were identified by 1H–1H gCOSY
cross-peaks and coupling patterns (Table 1b).
All quantitative 1H were run with a sufficient recycle
delay to allow for complete relaxation as determined by T1
analysis. 29Si NMR experiments were run with an empirically
determined recycle delay of 12 s even though the T1
values ranged from 50 to 55 s.[22] Determining the percent-
age of cis isomer present in samples of material 3c was com-
plicated by signal overlap around dH 7.50–7.47. For this
system, it was necessary to subtract the integrated value of
the protons at dH 6.60 (H-3b and H-3b´of cis 3c) from
that of dH 7.50–7.47 in order to determine the percentage of
cis isomer.
For comparative purposes, the percentage of the cis isomer in
various samples of 3a was also determined using 29Si NMR
spectra and compared with their 1H NMR counterparts (Table 3).
Analysis times for 29Si NMR spectra varied from 10 min to 12 h,
while all 1H NMR spectra were acquired in 13 min. Increasing
the time of acquisition for the proton experiment did not lead
to an appreciable change in calculated ratios. Contrariwise, as
the length of analysis time for 29Si NMR spectra was extended,
With the established 1H NMR chemical shift assignments,
integration was possible, and samples containing cis and trans
isomers could be quantified (Table 2).
Magn. Reson. Chem. 2013, 51, 490–496
Copyright © 2013 John Wiley & Sons, Ltd.
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B. W. Schoen, D. Holmes and A. Lee
concentrated, approximately 50 mg in 0.6 ml of solution,
whereas the 1H NMR spectra could be obtained with a con-
centration of < 5 mg in 0.6 ml of solution. Overall, more accu-
rate data was acquired with 1H NMR using less material and
shorter analysis time.
Conclusion
In this study, 1H–29Si gHMBC and 1H–1H gCOSY were used to
assign the chemical shifts of the protons for the cis and trans
isomers of DDSQ(m/p-AP)(Me) and DDSQ(m-AP)(Cy) as well as
to verify the chemical shifts of 29Si NMR. Once the proton
chemical shifts of these compounds were identified, a routine
access methodology to determine the cis and trans isomeric
ratio was developed. The method described herein offers a
more accurate quantification of the isomeric ratio in a shorter
analysis time using standard NMR equipment with less material
required per sample when compared to utilizing 29Si NMR
spectroscopy. With the ability to identify the isomeric ratios,
attempts to isolate the individual isomers can be made, and
the influence of stereo-configurations on the physical and
chemical properties of these hybrid nanostructured chemicals
can be studied and utilized.
Experimental
Solvents and Reagents
Tricycle[7.3.3(3,7)]octasiloxane-5,14,17-tetraol-1,3,5,7,9,11, 14,17-
octaphenyl (Ph8tetrasilanol-POSS) was obtained from Hybrid
Plastics (Hattiesburg, MS). Tetrahydrofuran (THF), hexanes, diethyl
ether, magnesium turnings, triethylamine, trichloromethyl silane,
and 3-[bis(trimethylsilyl)amino]phenyl-magnesium chloride were
obtained from Sigma-Aldrich. The solvents used for synthesis were
distilled under nitrogen and degassed using freeze–pump–thaw
methods for synthetic procedures. All deuterated solvents were
used as supplied by the vendor.
Figure 4. 1H–29Si gHMBC connectivity of (a) cis/trans 3a and (b)
cis/trans 3c.
the percentage of cis isomer determined approached the
percentages determined using the 1H NMR spectra. No
improvement was seen when extending 29Si experiments past
4 h. The limiting factor was the poorer signal-to-noise (S/N) in
the 29Si NMR spectra. This not only made it more difficult to
determine the limits of integration on 29Si NMR spectra as
compared to that of the 1H NMR spectra but also increased
the uncertainty in the former (Fig. 2). Even after 12 h, the
S/N of the 29Si NMR spectrum was not comparable to its
1H NMR spectrum (Table 3), which was run for 13 min. For
example, at 12h, the S/N of the smallest signal integrated was
19:1, and the S/N of the largest integrated signal was 64:1
Synthesis
DDSQ(m/p-AP)(R) was synthesized based on a described method,
except on a larger scale.[15]
Characterization
DDSQ(m/p-AP)(R) was measured at 25 ꢀC on a Varian UNITY-Inova
600 spectrometer equipped with a 5-mm pulsed-field-gradient
(PFG) switchable broadband probe and operating at 599.80 MHz
(1H) and 119.16 MHz (29Si). 1D 1H NMR data were acquired
using a recycle delay of 20 s and 32 scans to ensure accurate
integration. The pulse angle was set to 45ꢀ. The 1H-chemical
shifts were referenced to that of residual protonated solvent
in CDCl3 (7.24 ppm). 1D 29Si{1H} NMR data were acquired
using a recycle delay of 12 s with inverse-gated decoupling.
The pulse angle was set to 90ꢀ. 29Si{1H} spectra were
referenced against the lock solvent using vendor-supplied
lock referencing. All 2D NMR spectra were obtained using
gradient pulses on a 5-mm PFG switchable broadband probe
without sample spinning. Phase-sensitive spectra were
acquired using the hyper-complex States method. Threefold
linear prediction was applied to the F1 dimension as
implemented by standard Varian software. 1H-29Si gHMBC
1
(exp 5-29Si). The lowest and highest S/N for the H NMR spec-
trum of the same material was 49:1 and 239:1, respectively
(exp 5-1H). For mixtures containing predominately one isomer,
it becomes increasingly more difficult to accurately determine
isomeric purity. As an example, after 4 h, the 29Si NMR
spectrum of a sample that is majority cis isomer had an S/N
for the trans isomer signal of 2:1 while the S/N of the cis
isomer signal was 34:1 (exp 4-29Si). The signal representing
the trans isomer could potentially be mistaken for, or hidden
under, noise had the analysis time been shortened, the purity
of the cis isomer increased, or the concentration of the
sample decreased. All 29Si samples had to be heavily
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Magn. Reson. Chem. 2013, 51, 490–496

Quantification of cis and trans isomers in double-decker silsesquioxanes
Table 1. 29Si and 1H resonances of (a) cis/trans 3a and (b) cis/trans 3c
Atom
1H (mult.)
29Si (mult.)
a
1 (Si)
—
–79.4(2 Si)a, –79.6(4 Si)b, –79.8(2 Si)a
1-(C6H5)
-a,a0 (CH)
-b,b0 (CH)
-c (CH)
2 (Si)
—
7.16(m, 4H)a, 7.32(m, 8H)b,7.48(m, 4H)a
—
—
7.31(m, 4H)a, 7.15(m, 8H)b, 7.23(m, 4H)a
—
7.39(m, 4H)c, 7.38(m, 4H)c, 7.25(m, 4H)c, 7.10(m, 4H)c
—
—
–78.4 (8 Si)d
2-(C6H5)
-a,a0 (CH)
-b,b0 (CH)
-c (CH)
3 (Si)
—
—
7.54(m, 16H)d
—
7.24(m, 16H)d
—
7.39(m, 4H)c, 7.38(m, 4H)c, 7.25(m, 4H)c, 7.10(m, 4H)c
—
—
0.51 (s, 12H)c
—
–30.6 (4 Si)d
3-(CH3)
3-(C6H6N)
-a (CH)
-b (NH2)
-c (CH)
-d (CH)
-e (CH)
—
—
—
—
—
—
—
6.92 (m, 4H)
3.16 (s, 8H)d
6.67 (m, 4H)d
7.08 (m, 4H)d
7.03 (m, 4H)d
b
1 (Si)
—
–79.1(2 Si)a, –79.3(4 Si)b, –79.5(2 Si)a
1-(C6H5)
-a,a0 (CH)
-b,b0 (CH)
-c (CH)
2 (Si)
—
7.19(m, 4H)a, 7.33(m, 8H)b,7.50(m, 4H)a
—
—
7.32(m, 4H)a, 7.18(m, 8H)b, 7.20(m, 4H)a
—
7.39(m, 4H)c, 7.38(m, 4H)c, 7.25(m, 4H)c, 7.11(m, 4H)c
—
—
–78.2 (8 Si)d
2-(C6H5)
-a,a0 (CH)
-b,b0 (CH)
-c (CH)
3 (Si)
—
—
7.55(m, 16H)d
—
7.23(m, 16H)d
—
7.39(m, 4H)c, 7.38(m, 4H)c, 7.25(m, 4H)c, 7.10(m, 4H)c
—
—
0.51 (s, 12H)c
—
–29.7 (4 Si)d
3-(CH3)
3-(C6H6N)
-a,a0 (CH)
-b,b0 (CH)
-c (NH2)
—
—
—
—
—
6.53 (m, 8H)d
7.47 (m, 8H)d
3.69 (s, 8H)d
acis.
btrans.
cCannot distinguish between cis and trans.
dIsochronous cis/trans.
spectra were acquired with spectral widths of 6600 Hz and
14 370 Hz for F2 and F1, respectively.[23] The pre-acquisition
delay was set to 1.0 s, and 400 increments with eight
transients per increment containing 1069 data points were
acquired. The three-bond J-filter was set to 7 Hz (Varian
parameter; Jnxh = 7). Unshifted sine-bell windows, which were
matched to the acquisition time, were used for processing
both dimensions. Zero filling to 4096 data points was applied
to F1 prior to 2D Fourier transformation. 1H-1H gCOSY spectra were
obtained using a spectral width of 8000 Hz in both dimensions. The
pre-acquisition delay was set to 1.0 s and 128 increments with four
transients of 1152 data points were acquired. Both F2 and F1 were
multiplied by unshifted sine-bell weighting functions that were
matched to the acquisition or evolution time. Prior to 2D Fourier
transformation, F2 and F1 were zero filled to 2048 and 1024 data
points, respectively.
Table 2. Integrated values of 1H NMR spectra from various mixtures
of 3
Compound
d1
d2
Ratio
% cis
3a
0.05
4.08
16
3.13E–03
0.26
<1
51
99
53
50
27
85
16
16
16
16
16
16
7.91
0.49
3b
3c
4.24
0.27
12.35
10.04
15.77
0.77
0.63
0.99
Integrals are taken at the following d and can be seen in Figure 3.
3a: d1 = 7.48 ppm, d2 = 7.54 ppm.
3b: d1 = 7.48 ppm, d1 = 7.57 ppm.
3a: d1 = 7.50 + 7.47 ppm, d2 = 7.55 ppm.
Magn. Reson. Chem. 2013, 51, 490–496
Copyright © 2013 John Wiley & Sons, Ltd.
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B. W. Schoen, D. Holmes and A. Lee
Table 3. Integrated values of 1H NMR spectra versus 29Si NMR spectra
from various mixtures of 3a
[6] Y. Morimoto, K. Watanabe, N. Ootake, J. Inagaki, K. Yoshida, K. Ohguma,
US 0249103, 2003.
[7] A. Stein, B. J. Melde, R. C. Schroden. Adv. Mater. 2000, 12, 1403–1419.
doi:10.1002/1521-4095(200010)12:19 < 1403::aid-adma1403 > 3.0.
co;2-x.
Exp # Nucleus
Time
Ratio % cis S/N range (low–high)
1
2
3
4
5
29Si
1H
29Si
1H
29Si
1H
29Si
1H
10 min
13 min
30 min
13 min
2 h
0.43
0.26
0.43
0.25
0.48
0.25
0.97
0.49
0.37
0.2
43
51
43
49
48
51
97
99
37
39
6–15
57–183
11–28
52–201
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