Dicondensed indolinobenzospiropyrans as precursors of thermo- and photochromic spiropyrans. Part II: Assignment of 1H and 13C NMR spectra

Article abstract of DOI:10.1002/mrc.1718

The ¹H and ¹³C NMR spectra of dicondensed indolinobenzospiropyrans as precursors of thermo- and photochromic spiropyrans, DC1-DC5, were completely assigned. Especially, the ¹H assignment and coupling characteristics of the diastereotopic protons at the carbon-3 position of the benzopyran rings were achieved by conducting ¹H-¹H COSY and nOe experiments. The dihedral angles (θ₁, θ₂ and θ₃) calculated from the experimental values of the vicinal coupling constants (³J) of DC5 are in good agreement with the observed values in the solid state. All of the carbons in the DC dye molecules were investigated through a combination of heteronuclear 2D-shift correlation spectroscopy (HETCOR) and DEPT135. Copyright

Full text of DOI:10.1002/mrc.1718

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2006; 44: 90–94
Published online 31 October 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/mrc.1718
Spectral Assignments and Reference Data
on those of other compounds with analogous chemical shifts and
Dicondensed indolinobenzospiropyrans as
precursors of thermo- and photochromic
coupling constants, they were somewhat ambiguous, especially the
1H assignments of the pyran-ring protons.19 Having confirmed the
X-ray crystal structure of the DC molecule (DC5, R COOH), we are
now able to characterize DC molecules spectroscopically in detail.
We, thus, report herein the detailed 1H and 13C NMR spectroscopic
studies of the dicondensed spiropyran derivatives, DC1–DC5.
1
spiropyrans. Part II†: assignment of H and
13C NMR spectra
Sam-Rok Keum,1∗ Su-Mi Ahn,1 Se-Jung Roh,1
Su-Jin Park,1 Sung-Hoon Kim2 and Kwangnak Koh3
RESULTS AND DISCUSSION
1
Department of New Material Chemistry, Korea University, Jochiwon
Synthesis and characterization
339–700, South Korea
2
All dicondensed products (DC1–DC5) described in Scheme 1 are
amorphous solids and are stable at room temperature. The melting
points and yields of compounds DC1–DC5 are listed in Table 1.
Department of Dyeing and Finishing, Kyungpook National University,
Daegu 702–701, South Korea
3
°
When heated slowly to 130 ꢀ140 C, they quantitatively decompose
Department of Pharmacy, Pusan National University, Pusan 609–735,
to the corresponding spiropyran and the FB moiety.10
Structurally, spiropyran dyes consist of two ꢀ heterocyclic sys-
tems linked by a tetrahedral spirocarbon, whereas dicondensed
spiropyrans have three ꢀ components, namely the dihydrobenzopy-
ran ring (A), the indoline ring (B) and the methyleneindoline ring
(C), as shown in Scheme 1. In the solid state,10 the plane formed by
the indoline ring is parallel to the plane formed by the methylenein-
doline ring but orthogonal to the plane of the dihydrobenzopyran
ring.
South Korea
Received 4 July 2005; revised 24 August 2005; accepted 31 August 2005
The 1H and 13C NMR spectra of dicondensed indolino-
benzospiropyrans as precursors of thermo- and photo-
chromic spiropyrans, DC1–DC5, were completely
assigned. Especially, the 1H assignment and coupling
characteristics of the diastereotopic protons at the
carbon-3 position of the benzopyran rings were achieved
by conducting 1H–1H COSY and nOe experiments. The
dihedral angles (q , q and q ) calculated from the exper-
1H NMR assignment of DC1–DC5
The chemical shift values, e.g. H3, H3#, H4 and H200a, of DC1
were previously reported by our research group.19 The dicondensed
molecules DC1–DC5 show N-methyl peaks corresponding to the
indoline and methyleneindoline rings at υ 2.81–2.88 ppm and
3.04–3.08 ppm, respectively. These N-methyl chemical shifts are
comparable with those of 1,2,3,3-tetramethylindoline20 and the FB,
which were reported to be υ 2.70 and 3.15 ppm, respectively. The
excellent separation observed for the geminal dimethyl peaks makes
it possible to assign the resonances using nuclear Overhauser effect
(nOe) experiments.
1
2
3
imental values of the vicinal coupling constants (3J) of
DC5 are in good agreement with the observed values in
the solid state. All of the carbons in the DC dye molecules
were investigated through a combination of heteronu-
clear 2D-shift correlation spectroscopy (HETCOR) and
DEPT135. Copyright  2005 John Wiley & Sons, Ltd.
KEYWORDS: 1H NMR; 13C NMR; 2D NMR; dicondensed
indolinobenzospiropyrans; thermo- and photochromic spiropyrans
C30 is a prochiral center. The geminal 80 and 90-methyl groups
are in pro-S and pro-R positions respectively. Thus, H3 and H3#
are diastereotopic, and these two peaks are well separated at
υ 2.1–2.5 ppm, as reported earlier.19 Trace amounts of stereoisomers
of DC1 were detected without successful isolation. The geminal 80,90-
dimethyl groups of the indolino ring of DC1 appear characteristically
at υ 1.31 and 1.33 ppm, respectively.19 Irradiation of the H3 produced
an observable nOe on the signals at υ 1.33, 3.00 and 4.32 ppm
(90-methyl, H3# and H4, respectively). Irradiation of the 90-methyl
group produced an observable nOe on the signals at υ 2.23 and
4.32 ppm (H3 and H4 in benzopyran ring). H3 is, therefore, likely to
be close in space to the 90-methyl group. This conclusion is supported
by the observed chemical shift of H4 (υ 4.32 ppm), which evidences its
conjugation with both an olefinic bond and an aromatic moiety. The
stereochemistry ofthe enamine double bond canbe established onthe
basis of the observation of a strong nOe between the N-methyl group
of the methyleneindoline ring and the enamine proton H200a. Table 2
summarizes the 300 MHz 1H NMR chemical shifts and coupling
constants for the dicondensed spiropyran compounds examined in
the present study.
INTRODUCTION
Recently, thermo- and photochromic spiropyran dyes have gained
importance because of their potential utility in information record-
ing systems, high-density optical data storage, displays, holographic
devices, optical switches, and so forth.1,2 Spiropyrans are typical
organic photochromic compounds having high extinction coeffi-
cients in the near-infrared region and have been widely studied
from the chemical, physical, and material points of view.3–9
Dicondensed materials [DC, 4-(2-methylene-1,3,3-trimethy-
lindoline-20-yl)-10,30,30-trimethylspiro(3,4-dihydro-2H-1-benzopy-
ran-2,20-indoline)] are formed together with monocondensed materi-
als [SP, 1’,30,30-trimethylspiro(2H-1-benzopyran-2,20-indoline)] from
the condensation reaction of an excess of Fischer base (FB) with
substituted salicylaldehydes, as shown in Scheme 1.
Dicondensed spiropyran molecules are often referred to as
precursors of SP molecules since those DC molecules may transform
to the corresponding SP molecules thermally10 or by acid.11 DC
molecules have thus been used in many practical applications in
various fields, e.g. additives in silver halide emulsion12 and as
components of thermal papers.13,14
The dihedral angles (Â1, Â2 and Â3 in Fig. 1) for DC5 in
CDCl3 were calculated from the experimental values of the vicinal
coupling constants (3J) of DC5 using the Garbisch equation21
which is known as a modified Karplus equation describing the
conformation for vinylic–allylic proton spin couplings. The angles
Â1 and Â2 denote the dihedral angles of H4–C4–C3–H3 and
H4–C4–C3–H3# respectively; Â3 represents the dihedral angles
of H4–C4–C200a–H200a. The Garbisch equation21 is described in
Although these dicondensed products have provoked a consid-
erable amount of discussion in the past,15–18 their structures could
not be assigned unequivocally until our very recent work10 involving
the X-ray crystal analysis of the dicondensed products. Since the pre-
vious NMR assignments of these DC compounds were mainly based
°
Eqn (1) for the cases where  ꢁ 90 and Eqn (2) for the cases where
°
°
90 < Â ꢁ 180 .
ŁCorrespondence to: Sam-Rok Keum, Department of New Material
Chemistry, Korea University, Jochiwon 339–700, South Korea.
E-mail: keum@korea.ac.kr
3
2
2
°
J D 6.6 cos  C 2.6 sin  ꢁ ꢁ 90 ꢂ
ꢁ1ꢂ
ꢁ2ꢂ
3
2
2
°
°
J D 11.6 cos  C 2.6 sin  ꢁ90 <  ꢁ 180 ꢂ
†Part 1: Ref. 10.
Contract/grant sponsor: Basic Research Program of the Korea Science and
Engineering Foundation; Contract/grant number: R01-2003-000-10248-0.
Dihedral angles calculated from the experimental values of the
3
°
°
°
Contract/grant sponsor: Brain Korea 21 project.
vicinal coupling constants ( J) of the DC5 are 51 , 171 and 172 for
Copyright  2005 John Wiley & Sons, Ltd.

91
Spectral Assignments and Reference Data
Scheme 1
Table 1. Characteristics of the DC molecules prepared in this study
°
Melting point ( C)
Analysisd
H
Molecular
weight
Molecular ion m/z
(relative intensity %)
Compound
a
b
Color
Yieldc (%)
82
C
N
DC1
137
176
Yellow
Calculated 75.1 6.71 8.48
Found 74.9 6.80 8.57
Calculated 80.1 6.90 10.1
Found 80.6 6.88 10.2
Calculated 53.0 4.59 3.99
Found
(36.1)e
Calculated 77.8 6.71 12.6
Found 77.6 6.68 12.6
Calculated 77.7 6.93 5.66
Found 77.2 7.10 5.78
495.6
554.7
702.4
555.7
494.6
174 (100), 323 (33.2), 496 (4.13)
174 (100),105 (35.4), 555 (0.46)
174 (100), 214 (45.7), 703 (2.49)
174 (100), 156 (41.0), 556 (4.24)
174 (100), 105 (23.5), 495 (4.39)
DC2
DC3
DC4
DC5
142
148
140
133
170
177
172
167
Yellow
73
90
62
75
Pinkish white
Yellow- green
Light pink
a Temperatures at which DC decomposes to SP and FB before melting.
b Final melting temperatures.
c Yields calculated on the basis of the amounts of salicylaldehydes used.
d Values of DC-1, DC-2 and DC-5 were obtained from Ref. 1.
e Value for the element I.
quarternary carbons carrying the methyl groups, one methylene and
one methine group of the benzopyran ring. DC2 and DC4 have
additional aromatic carbons that belong to the azoaryl group.
Heteronuclear 2D correlation spectra (HETCOR) and DEPT135
were used for the assignment of the 13C spectral data of the DC
molecules.22,23 Pairwise couplings could be identified from the
HETCOR analysis. The seven aromatic and six aliphatic carbons are
coupled with 13 protons assigned previously. Substituent-induced
shift increments23 and DEPT135 spectra were used to assign the
remaining 17 carbons.
The methyl carbons bound to C30 are diastereotopic, since C2,20
and C4 are chiral centers. The 80 and 90 methyl groups are, thus,
expected to have different chemical shifts. The signals of the geminal
methyl groups 90 and 80 appear at υ 21.94 and 26.21 ppm respectively.
Interestingly, the pro-S methyl carbon (C80) resonates in a higher-
frequency region than the pro-R methyl carbon (C90), in contrast
to the 1H NMR signals where the 90 methyl protons resonate at
a higher-frequency region than the 80 methyl protons. It has also
been reported3 that for the S-epimer of 6-nitrospirobenzopyran, the
pro-S methyl group (H80) resonates at υ 1.24 ppm, while the pro-R
methyl group (H90) appears at υ 1.37 ppm in the 1H NMR spectrum.
The values of the N-methyl chemical shifts, υ 29.93 (indoline ring)
and 31.28 ppm (methyleneindoline ring), are slightly shifted toward
higher frequencies from the value of υ 28.69 ppm observed for 1,2,3,3-
tetramethylindoline.22 It turned out that the chemical shifts of C70
and C2,20 were too close to be resolved in the HETCOR spectrum.
However, they were well differentiated in the DEPT135 spectrum,
since C2,20 is a quaternary carbon and, therefore, not present.
Figure 1. Newman projections of DC5.
Â1, Â2 and Â3 respectively. These calculated values are compared with
°
°
°
those (52 , 171 and 172 for Â1, Â2 and Â3 respectively) in the solid
state for DC5 and revealed a good agreement.
13C NMR assignment of DC1–DC5
In the 13C NMR spectra of the DC molecules, 20 strong signals
were observed in the aromatic region of υ 105–161 ppm and one
0
spirocarbon (C2,2 ) resonating at ca υ 104 ppm. The remaining 11
signals in the aliphatic region (υ 21.94–49.55 ppm) belong to the
six methyl groups (four geminal dimethyl and two N-methyl), two
Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2006; 44: 90–94

92
Spectral Assignments and Reference Data
Table 2. 1H NMR spectral data of DC1–DC5, in CDCl3
Ringa
Proton
SPb
FB
DC1
DC2c
DC3
DC4d
DC5
Ring A
H3
H3#
–
6.01
7.20
8.13
8.03
6.83
7.16
6.83
7.12
6.60
1.17
1.28
2.74
–
–
–
2.23
3.00
4.32
8.23
7.96
6.75
7.07
6.83
7.06
6.59
1.31
1.33
2.85
4.15
7.11
6.86
7.09
6.60
1.62
3.05
14.3
13.0
4.9
2.24
2.45
4.37
7.93
7.79
6.82
7.19
6.75
7.08
6.57
1.34
1.38
2.87
4.26
7.22
6.85
7.09
6.57
1.67
3.06
14.2
12.0
4.9
2.12
2.38
4.22
7.52
7.82
–
2.19
2.47
4.37
8.01
7.72
6.84
7.20
6.78
7.10
6.58
1.35
1.39
2.88
4.25
7.21
6.84
7.10
6.58
1.68
3.08
14.1
12.0
4.7
2.19
2.43
4.27
8.06
7.81
6.75
7.18
6.78
7.10
6.56
1.25
1.26
2.85
4.16
7.19
6.86
7.15
6.59
1.56
3.04
14.1
12.0
4.2
H4
–
H5
–
H7
–
H8
H 40
H 50
H 60
–
Ring B
Ring C
J (Hz)
–
7.15
6.77
7.07
6.56
1.31
1.33
2.81
4.10
7.18
6.83
7.07
6.56
1.58
3.04
14.2
12.2
4.9
–
–
H 70
–
Me- 80
Me- 90
N-Me(100)
H200ae
H400
H500
H600
–
–
–
4.00
7.22
6.90
7.26
6.66
1.50
3.15
–
–
–
–
H700
–
Me800 and 900
N-Me(1000)
H3- H3#
H3#-H4
H3-H4
H4-H200a
H3-H4
H5-H7
H7-H8
–
–
–
–
–
–
–
–
–
10.1
–
10.0
–
10.1
–
10.1
–
11.3
–
10.5
2.0
9.0
–
–
2.6
2.0
1.7
2.5
2.4
–
8.8
8.6
–
8.8
8.7
a Rings A, B and C denote the benzopyran, indoline and methyleneindoline ring moieties, respectively.
b Data of SP (60-NO2ꢂ in acetone-d6 taken from Ref. 4.
c 1H chemical shifts of the azophenyl group are υ 7.79 and 7.42 ppm for Ho and Hm,p, respectively.
d 1H chemical shifts of the pyridine side group are υ 8.61, 7.35, 8.04, and 9.07 ppm for H2, H4, H5, and H6, respectively.
e Olefinic proton.
The 13C chemical shifts of the aromatic carbons were calculated
using the incremental shifts reported for OCH3, isopropyl and nitro
substituents.23 The assignments of the aromatic carbons, C4a, C5,
C6, C7 and C8 were made by adding the substituent effects for the
OCH3, isopropyl and nitro substituents to the observed values with
those calculated for DC1 observing a reasonably good agreement
between calculated and observed values. Table 3 summarizes the
13C NMR chemical shifts for all of the DC compounds in the present
study.
melting points and yields of the compounds DC1–DC5 are listed in
Table 1.
NMR spectral measurements
The 1D and 2D 1H and 13C NMR spectra were recorded with a
Varian Mercury 300 NMR spectrometer, operating at 300.07 MHz
for 1H and 75.46 MHz for 13C. The samples were 0.1 M solutions
in DMSO-d6 in 5-mm NMR tubes, and the spectra were recorded
at 298 K. 1H and 13C chemical shifts were referenced to SiMe4
in CDCl3 as internal standard or to the residual solvent signal
in DMSO-d6 (1H, υ 2.50 ppm and 13C, υ 39.52 ppm). The digital
resolution of the 1H and 13C NMR spectra were 0.25 and 0.6 Hz per
point, respectively. Narrower spectral regions of special interest were
measured with smaller spectral widths and larger digital resolutions
(down to 0.2 Hz). The following techniques were used: BB–1H-
EXPERIMENTAL
Materials
Fischer’s base (2-methylene-1,3,3-trimethylindoline) and salicylalde-
hyde were obtained from Aldrich Chemical Co. and used without
further purification.
noise decoupling, attached proton test, 1H–1H COSY and 1H–13
C
HETCOR. The 1H–1H COSY spectra were obtained in the magnitude
mode with 1024 points in the F2 dimension and 256 increments in the
F1 dimension. Each increment was obtained with 16 scans, a spectral
width of 4500 Hz and a relaxation delay of 1 s. The resolutions were
5.4 and 10.7 Hz per point in the F1 and F2 dimensions, respectively.
The 1H–13C HETCOR spectra were measured with the one-bond
13C, 1H coupling constant set to 140 Hz using 2048 points in the F2
dimension and 256 increments in the F1 dimension with a relaxation
delay of 1 s. The spectral width was 20 000 Hz in the F2 and 4500 Hz
Dicondensed compounds DC1–DC5 [6-substituted 4-(2-methy-
lene-1,3,3-trimethylindoline-20-yl)-10,30,30-trimethylspiro [3,4-dihy-
dro-2H-1-benzopyran-2,20-indoline] were obtained from the reaction
of 5 to 10 molar excess of FB and the substituted salicylaldehydes
in absolute ethanol. The yellow precipitate was filtered from the hot
ethanolic solution and washed thoroughly with cold diethyl ether in
order to remove the monocondensed molecule (SP). Purification was
carried out by recrystallization from chloroform/diethylether. The
Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2006; 44: 90–94

93
Spectral Assignments and Reference Data
Table 3. 13C NMR spectral data of DC1–DC5, in CDCl3
13C chemical shift (ppm)
Ringa
Carbon
SPb
FBb
DC1
DC2c
DC3
DC4d
Ring A
C2,20
C3
106.4
121.5
128.2
118.6
125.8
140.9
122.6
115.4
159.8
52.2
136.1
121.6
119.7
127.8
107.0
147.7
25.9
19.9
28.8
–
–
104.8
33.0
103.5
33.5
104.6
33.2
103.8
33.4
–
C4
–
31.1
31.3
31.9
31.3
C4a
–
126.7
125.5
140.8
121.5
119.3
156.3
44.4
126.1
121.1
152.9
120.9
116.9
158.6
44.3
129.3
137.7
86.20
144.8
82.03
155.7
44.3
126.3
123.8
137.2
126.7
117.1
159.3
44.3
C5
–
C6
–
–
C7
C8
–
C8a
C 30
C30a
C 40
C 50
C 60
C 70
C70a
C 80 Me
C 90 Me
C 100 N-Me
C200
C200a
C300
C300a
C400
C500
–
Ring B
–
–
136.9
121.2
118.5
127.9
104.7
148.3
26.2
137.3
121.4
119.0
127.0
104.8
148.7
26.3
137.7
121.0
119.1
121.4
104.9
153.8
26.2
137.5
121.2
119.0
127.0
104.8
148.7
26.2
–
–
–
–
–
–
–
21.9
22.0
22.3
22.0
–
28.2
28.3
28.1
28.3
Ring C
161.8
73.5
43.4
136.7
121.4
118.6
127.3
104.9
145.9
29.5
28.3
161.4
95.1
146.5
96.7
148.6
95.4
155.5
96.4
–
–
49.6
49.4
49.3
49.4
–
137.5
127.9
116.6
124.4
105.1
145.9
29.9
137.8
127.8
118.2
127.0
107.3
146.1
30.1
137.5
127.9
118.4
127.6
107.5
145.9
29.9
146.0
126.7
118.2
127.0
107.3
146.5
30.1
–
–
C600
C700
–
–
C700a
C800 and 900 Me
C1000 N-Me
–
–
–
29.2
29.2
29.2
29.2
a Rings A, B and C denote benzopyran ring, indole, and methyleneindolenine ring, respectively.
b Data for 6-nitroindolinobenzospiropyran taken from Ref. 4.
c 13C chemical shifts are υ 148.1, 147.0, 150.7, 127.8, and 121.4 ppm for the C1 –C2 and C4 –C6 of the
azo-(3)-pyridinyl group, respectively.
d 13C chemical shifts are υ 155.4, 122.5, 128.9, and 130.0 ppm for the Ciso, Cortho, Cbeta and Cpara carbons
of azophenyl group, respectively.
in the F1 dimension. The resulting resolution was 19.53 Hz per
2. Du¨rr H, Bouas-Laurent H (eds). Photochromism: Molecules and
Systems. Elsevier: Amsterdam, 1992.
3. Keum SR, Lee KB, Kazmaier PM, Buncel E. Magn. Reson. Chem.
1992; 30: 1128.
4. Keum SR, Shin JT, Lee SH, Shin ST. Mol. Cryst. Liq. Cryst. 2004;
411: 119.
5. Keum SR, Lee SH, Kang SO. Liq. Cryst. 2004; 31: 1.
6. Keum SR, Choi YK, Lim SS, Kim SH, Koh KN. Magn. Reson.
Chem. 2005; 43: 873.
point in the F2 and 17.6 Hz per point in the F1 dimension. All
two-dimensional experiments were performed by standard pulse
sequences using the Mercury Data System software Version VNMR
6.1B. For proton decoupling, the Waltz 16 modulation was used.
Acknowledgements
This work was supported in part by grant no. R01-2003-000-10248-0
from the Basic Research Program of the Korea Science and
Engineering Foundation and in part by the Brain Korea 21 project in
2003.
7. Meirovitch E, Shvartman FP, Krongauz VA, Zimmermann H. J.
Phys. Chem. 1985; 89: 5522.
8. Irie M, Iwayanagi T, Taniguchi Y. Macromolecules 1985; 18: 2418.
9. Swansberg S, Bunce E, Lemieux RP. J. Am. Chem. Soc. 2000; 122:
6594.
REFERENCES
10. Keum SR, Ku BS, Shin JT, Ko JJ, Buncel E. Tetrahedron 2005; 61:
6720.
11. Yun IK. Thesis of Master of Science. Korea University: Seoul, 1992.
1. Crano JC, Guglielmetti RJ. Organic Photochromic and Ther-
mochromic Compounds. Plenum Press: New York and London,
1999; 11.
Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2006; 44: 90–94

94
Spectral Assignments and Reference Data
12. Baralle RM, Compere MA, Praff ME, Jordi FX, Goumount CG.
Fr. Demande FR 2491638 Al, 1982; CA 95(4): 33421c.
13. Ricoh Co., Ltd. Jpn. Tokkyo Koho JP 55035277, 1980; CA 95:
33421c.
14. Samat A, Guglielmetti R, Metzger J. Fr. Demande, FR 2271938,
1975; CA 85(16): 114776t.
15. Koelsch CF, Workman WR. J. Am. Chem. Soc. 1952; 74: 6288.
16. Schiele C, Arnold G. Tetrahedron Lett. 1968; 245.
17. Hinnen A, Audic C, Gautron R. Bull. Soc. Chim. Fr. 1968; 2066.
18. Balny C, Hinnen A, Mosse M. Tetrahedron Lett. 1968; 5097.
19. Keum SR, Kazmaier PM, Cheon KS, Manderville RA, Buncel E.
Bull. Korean Chem. Soc. 1996; 17: 391.
20. Bertelson RC. J. Org. Chem. 1965; 30: 2875.
21. Garbisch EW Jr. J. Am. Chem. Soc. 1964; 86: 5561.
22. Silverstein RM, Webster FX. Spectrometric Identification of Organic
Compounds (6th edn). Wiley: New York, 1998; 229.
23. Pretsch E, Clerc T, Seibl J, Simon W. Tables of Spectral Data for
Structure Determination of OrganicCompounds(2nd edn). Springer-
Verlag: Berlin, 1989; C120.
Copyright  2005 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2006; 44: 90–94