Intermolecular hydrogen-bonding effects on the amide oxygen electric- field-gradient and chemical shielding tensors of benzamide [2]

Full text of DOI:10.1021/ja9939789

J. Am. Chem. Soc. 2000, 122, 4215-4216
Intermolecular Hydrogen-Bonding Effects on the
4215
Amide Oxygen Electric-Field-Gradient and Chemical
Shielding Tensors of Benzamide
,†
†
†
Gang Wu,* Kazuhiko Yamada, Shuan Dong, and
Hiltrud Grondey‡
Department of Chemistry, Queen’s UniVersity
Kingston, Ontario, Canada, K7L 3N6
Department of Chemistry, UniVersity of Toronto
Lash Miller Bldg., 80 St. George Street
Toronto, Ontario, Canada, M5S 3H6
ReceiVed NoVember 12, 1999
ReVised Manuscript ReceiVed February 15, 2000
Recent advances in experimental solid-state nuclear magnetic
resonance (NMR) and computational chemistry have made it
possible to establish the correlation between second-rank NMR
tensors and molecular structure.1 Several studies have demon-
strated the influence of intermolecular interactions on chemical
-5
shielding tensors for 1H, C, and N nuclei.
13
15
6-15
However,
17
relatively little is known about O chemical shielding tensors,
despite the enormous importance of oxygen-containing functional
groups in chemistry and biology. In this contribution we report a
new experimental determination of the 1 O electric-field-gradient
7
(EFG) and chemical shielding (CS) tensors for an amide functional
group. We also demonstrate the importance of including inter-
molecular hydrogen-bonding (HB) interactions in quantum chemi-
Figure 1. Experimental (upper trace) and calculated (lower trace) solid-
state 17O NMR spectra of [ O]benzamide: (A) MAS, 11.75 T, sample
spinning frequency ) 15 kHz, (B) stationary, 11.75 T, and (C) stationary,
9.40 T.
17
1
7
cal calculations of O EFG and CS tensors.
Figure 1 shows the 17O magic-angle spinning (MAS) and
1
7
16
stationary NMR spectra of [ O]benzamide. From the analysis
of the 17O MAS spectrum, we obtained the following NMR
shielding, δ33, is approximately parallel to Vxx, and that the angle
between δ11 and Vzz is 72°. It is important to point out that one
2
parameters: δiso ) 300.0 ( 0.5 ppm, ø ) e QVzz/h ) 8.40 (
17
0.05 MHz, and η
Q
) 0.37, where Vzz is the largest principal
must exercise caution in interpreting stationary O NMR spectra
because, in many cases, multiple solutions may exist. This
component of the EFG tensor, |Vzz| > |Vyy| > |Vxx|, and η
asymmetry parameter defined as η ) (Vxx - Vyy)/Vzz. Following
the standard procedure, we were able to analyze the stationary
Q
is the
1
7
Q
ambiguity is easily removed by obtaining stationary O NMR
spectra at multiple magnetic fields.
17
1
7
It is well-known that analysis of solid-state 17O NMR spectra
yields only the relatiVe orientation between the EFG and CS
tensors. To determine tensor orientations in the molecular frame
of reference, we decided to perform quantum chemical calcula-
tions for the 17O EFG and CS tensors in benzamide. Although
several groups have reported reasonably good agreement between
O NMR spectra shown in Figure 1 and obtain the principal
1
7
components of the O CS tensor: δ11 ) 500 ( 2, δ22 ) 400 (
, and δ33 ) 0 ( 2 ppm, R ) 6 ( 4°, â ) 90 ( 1°, and γ ) 72
1°. These results indicate that the direction of the strongest
2
(
*
Corresponding author. Phone: 613-533-2644. Fax: 613-533-6669. E-
mail: gangwu@chem.queensu.ca.
†
17
18-24
Queen’s University.
University of Toronto.
experimental and calculated O isotropic chemical shifts,
‡
1
7
(
1) Tossell, J. A., Ed. Nuclear Magnetic Shieldings and Molecular
(16) Benzoic acid- O
2
was obtained by reacting 0.3850 g (2.0 mmol) of
1
7
Structure; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1993.
2
R,R,R-trichlorotoluene with 0.0720 g (4.0 mmol) of H O* (50.8% O atom
(
2) Jameson, C. J. In Modeling NMR Chemical Shifts: Gaining Insight
purchased from ISOTEC, Miamisburg, Ohio) in a sealed tube at approximately
120 °C for 15 h. HCl gas was removed after cooling the sealed tube to room
temperature. The remaining white crystalline products were recrystallized from
into Structure and EnVironment; Facelli, J. C., de Dios, A. C., Eds.; ACS
Symp. Ser. No. 732; Oxford University Press: Oxford, 1999.
1
7
(3) Sitkoff, D.; Case, D. A. Prog. Nucl. Magn. Reson. Spectrosc. 1998,
acetone/petroether. Yield: 93%. [ O]Benzoyl chloride was obtained by
17
3
2, 165.
4) Chesnut, D. B. Annu. Rep. NMR Spectrosc. 1989, 21, 51. Chesnut, D.
refluxing thionyl chloride and benzoic acid- O
2
(molar ratio of 1.1:1) for 1
(
h, and subsequently removing the excessive thionyl chloride by distillation.
1
7
B. Annu. Rep. NMR Spectrosc. 1994, 29, 71.
To [ O]benzoyl chloride was added dropwise a cold ammonia-methanol
solution until the temperature was stabilized, and the solution was stirred at
room temperature for 3 h. The solution was then poured into water followed
(
5) Berglund, B.; Vaughan, R. W. J. Chem. Phys. 1980, 73, 2037.
6) Wu, G.; Freure, C. J.; Verdurand, E. J. Am. Chem. Soc. 1998, 120,
(
17
1
3187.
by extraction with diethyl ether. The white product of [ O]benzamide (50.8%
17
(
7) Asakawa, N.; Kameda, T.; Kuroki, S.; Kurosu, H.; Ando, S.; Ando, I.;
O atom) was obtained upon removal of the solvent. The melting point,
solution NMR, and IR results are in agreement with the literature values. Solid-
Shoji, A. Annu. Rep. NMR Spectrosc. 1998, 35, 55 and references therein.
1
7
(
8) de Dios; A. C.; Pearson, J. G.; Oldfield, E. Science 1993, 260, 1491.
9) de Dios, A. C.; Laws, D. D.; Oldfield, E. J. Am. Chem. Soc. 1994,
state O NMR spectra were recorded on Bruker Avance-500 and Avance-
17
(
400 NMR spectrometers. In the static O NMR experiments, a Hahn-echo
sequence was used to eliminate the acoustic ringing of the probe.
(17) (a) Cheng, J. T.; Edwards, J. C.; Ellis, P. D. J. Phys. Chem. 1990, 94,
553. (b) Power, W. P.; Wasylishen, R. E.; Mooibroek, S.; Pettitt, B. A.;
Danchura, W. J. Phys. Chem. 1990, 94, 591.
1
1
1
16, 7784.
(
10) de Dios, A. C.; Oldfield, E. J. Am. Chem. Soc. 1994, 116, 11485-
1488.
(
11) Malkin, V. G.; Malkina, O. L.; Salahub, D. R. J. Am. Chem. Soc.
995, 117, 3294.
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Chem. Soc. 1995, 117, 1851.
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Z.; Facelli, J. C.; Poulter, C. D.; Grant, D. M. J. Phys. Chem. 1995, 99, 10454.
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18, 5488-5489.
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02, 499.
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J. F. J. Chem. Phys. 1996, 104, 2574.
(
1
(
(21) Barszczewicz, A.; Jaszunski, M.; Jackowski, K. Chem. Phys. Lett.
1993, 203, 404.
(
(22) Olah, G. A.; Burrichter, A.; Rasul, G.; Gnann, R.; Christe, K. O.;
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3
1
0.1021/ja9939789 CCC: $19.00 © 2000 American Chemical Society
Published on Web 04/12/2000

4216 J. Am. Chem. Soc., Vol. 122, No. 17, 2000
Communications to the Editor
interactions also cause a more shielded environment at the amide
17
oxygen nucleus (i.e., a smaller isotropic O chemical shift value).
The principal component corresponding to the least shielding, δ11
,
exhibits a remarkable sensitivity (ca. 152 ppm) to the HB
interaction, whereas the change in the most shielded component,
δ
33, is quite small, ca. 25 ppm. Since the changes in δ11 and δ33
17
are of the opposite signs, the span of the O chemical shift tensor
exhibits a change of 177 ppm on going from the isolated molecule
to the trimer. The calculated orientations of the 17O CS and EFG
tensors are depicted in Figure 2B. Interestingly, the calculations
indicate that the orientations of both the 17O EFG and CS tensors
remain unchanged within 5° among the different models. This is
consistent with a previous theoretical study on the hydration of
34
glycylglycine. As also seen from Table 1, the calculated relative
orientation between the 17O EFG and CS tensors is in excellent
agreement with that determined experimentally.
It should be emphasized that the absolute 17O CS tensor
orientation depicted in Figure 2B is quite different from that
reported by Ando and co-workers for amide functional groups.
In particular, based on solid-state O NMR and finite perturbation
theory (FPT) MNDO-PM3 calculations, these authors concluded
Figure 2. (A) Hydrogen-bonding environment in benzamide determined
by a neutron diffraction study.25 (B) Orientations of the O EFG and CS
tensors in benzamide. Both δ33 and Vxx are perpendicular to the amide
plane.
17
3
5
Table 1. Calculated (B3LYP/D95**) and Experimental 17O CS
and EFG Tensors of the Amide Oxygen in Crystalline Benzamide
17
a,b
ø/
R/
â/
γ/
17
that δ11 of the O CS tensor for an amide oxygen is perpendicular
system
isolated
molecule
δ
iso
δ
11
δ
22
δ
33 MHz
η
Q
deg deg deg
to the CdO bond. However, for a carbonyl oxygen atom, the
dominant contribution to the paramagnetic shielding is expected
to be the n T π* mixing. Consequently, the direction along the
CdO bond should give rise to the least shielded environment at
379
674 487 -24 10.19 0.24 7.7 88.7 77.7
linear dimer 351
cyclic dimer 329
608 455 -10 9.75 0.34 4.5 89.0 76.4
573 426 -13 9.17 0.43 6.4 89.0 75.0
17
the oxygen nucleus. For example, a single-crystal O NMR study
trimer
exptl
a
308
522 402
1
8.77 0.53 4.3 89.6 73.3
36
17
by Haeberlen and co-workers showed that δ11 of the O CS
300.0 500 400
0
8.40 0.37 90 72
6
2
tensor in benzophenone, Ph CdO, is along the direction of the
CdO bond. The orientation of the 17O CS tensor for benzamide
reported in this study is also in good agreement with the DFT
calculation for the complex of N-methylacetamide with two water
All chemical shifts are in ppm and relative to liquid water. Errors
in the experimental principal components of the CS tensor are (2 ppm.
The computed absolute shielding values are converted to chemical shifts
1
7
31
b
3
17
using σ( O, H
2
O, liquid, 300 K) ) 307.9 ppm.
The calculated
molecules. We have also performed numerous O chemical
shielding calculations on a number of model amides and dipep-
tides, and all the calculations predict O CS tensor orientations
2
values of Vzz are converted to ø using ø [MHz] ) 2.3496Q[fm ]Vzz[au],
3
2
where Q ) -2.558 as recommended by Pyykk o¨ .
17
similar to that of benzamide. This orientation is further confirmed
most authors did not comment on the accuracy of the calculated
principal components. In the present study, we used several
molecular cluster models in the calculations to evaluate the
influence of intermolecular HB interactions on 17O NMR tensors.
The first cluster model is a linear dimer consisting of Mol1 and
Mol2 as defined in Figure 2A. The second cluster is a cyclic
dimer, Mol1 and Mol3. The third model is a trimer formed by
Mol1, Mol2, and Mol3. The experimental neutron diffraction
13
17
by the results of a C- O dipolar-chemical shift NMR study
13 17
37
on [ C, O]benzamide. All these studies support the tensor
orientation depicted in Figure 2B.
In summary, we have presented new experimental and theoreti-
17
cal results on the magnitude and orientation of the O CS and
EFG tensors in benzamide. We have also demonstrated that it is
important to include a complete HB network in the quantum
17
chemical O NMR calculations. The present study suggests that
25
structure of benzamide was used in all the models.
17
O is a remarkably sensitive nuclear probe to HB interactions,
1
7
26
The calculated O NMR results are summarized in Table 1.
and is therefore potentially useful for structural studies of proteins.
17
The value of ø( O) shows a strong dependence on the HB
17
We are presently investigating the syntheses, solid-state O NMR,
environment. In general, the presence of the CdO‚‚‚H-N
and quantum chemical calculations of model peptides.
17
hydrogen bonds causes a reduction in ø( O). This is in qualitative
agreement with previous 17O NQR studies. The strong HB
33
Acknowledgment. This research was supported by the Natural
Sciences and Engineering Research Council (NSERC) of Canada.
(
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2
7
2
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the Gaussian 98 program. The Dunning/Huzinaga full double-ú basis set
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