- Email: [email protected]
Additivity in the deuterium quadrupole coupling constants of azines
JOURNAL
OF MOLECULAR
SPECTROSCOPY
Additivity in the Deuterium
138, 3 15-3 17 (1989)
Quadrupole
Coupling Constants
of Azines
A previously developed concept for the calculation of deuterium quadrupole coupling constants using basis sets of local high quality is applied to benzene and related azines. The deuterium quadrupole coupling constant is strongly correlated to the bond length, but in this work the bond length is kept constant to study the additional direct effects of the electronic structure changes in this class of compounds. It is found that the coupling constants of the higher azines can be ~1 ,989 Academic predicted by additive increments obtained from the couplings in pyridine. press. Inc.
As is well known the deuterium quadrupole coupling constants along the bond direction are strongly dependent on the bond length between deuterium and its neighbor. They can be well predicted with a relation given in previous papers ( 1, 2) taking into account the dependence on the bond length and applying an additional small empirical correction utilizing CNDO charge orders ( 1) or electronegativities (2). Here we investigate in more detail these second-order effects. For this purpose we keep the bond length between the deuterium and its neighbor as well as the type of neighboring atom constant and introduce nitrogen atoms in positions further away. This is performed on the following molecules: benzene, pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, and s-tetrazine. In most molecules there are several different positions resulting in 12 different couplings. The differences in the couplings are quite small (the full range being about 10 kHz) but as the compounds are very closely related, the differences in the calculated values are fairly accurate even if we apply only the SCF-level of approximation. The calculations were performed with the basis set given in Ref. ( 1). The concept of basis sets with local high quality allows one to calculate the couplings in these fairly large molecules with the same accuracy as in the smaller ones without prohibitively long computing times. The structure was taken from experiment except for the crucial bond length between the deuterium and its neighbor, which was kept constant at 108.5
TABLE I Calculated
Coupling
Tensors (in kHz, Conversion Factor 672.0 kHz/au). x is Along the Bond. y in the Plane, and z Vertical to the Plane of the Ring
Molecule
xx
Benzene
194.0
-91 .o
Pyridine-2-d,
-90.4
-99.9
-1.4
Pyridine-3-d,
190.3 192.8
-90.0
-102.8
0.2
Pyridine-4-d,
192.1
-92.1
-100.0
YY
zz
xY
-103.0
Pyridazine-3-d,
100.7
-89.4
-99.3
Pyridazine-4-d,
189.9
-91.1
-98.8
Pyrimidine-2-d,
167.0
-90.7
-96.2
Pyrimidine-4-d,
166.5
-91.4
-97.1
Pyrimidine-5-d,
191.7
-89.0
-102.6
Pyrazine
189.0
-89.2
-99.7
s-Triazine
184.8
-91 .o
-93.8
s-Tetrazine
183.2
-86.9
-96.3
4.6 -1.5 2.6 2.7
0022-2852/89 Copyright 0
$3.00
1989 by Academic Press, Inc.
All rights of reproduction in any form m.md
315
316
NOTES TABLE II
Increments for the o, m, and p Positions Relative to a Nitrogen, Obtained from a Linear Regression (in kHz, Conversion Factor 672.0 kHz/au) position
xx
YY
22
ortho
-3.65
0.53
3.13
meta para
-1.49 -2.07
1.20 -1.10
0.30 3.15
pm for reasons given above (for most azines this latter bond length is anyway not very accurately known experimentally). In detail the structures were taken from the following references: benzene (3), pyridine (4)) pyridazine (5), pyrimidine (6)) pyrazine ( 7)) s-triazine (8) and s-tetrazine ( 9). Table I lists the calculated coupling tensors. Although these values cannot be compared directly to experimental values as the crucial bond length is kept constant in the calculation, it may be of interest to give here a few experimental values available {all along the bond or the principal axes of the quadrupole coupling tensor). For benzene van Zijl et al. (10) have published a value of 240 k 20 kHz measured by NMR in the gas phase. This value seems to be far too high. For the same molecule M. Oldani et al. (1 I) determined the gas-phase value of 223 + 12 kHz, which has been corrected to 186.1 + 1.8 kHz in a molecular beam measurement ( 12). Liquid crystal measurements were given by Diehl and Reinhold ( 13) with 190.5 +_ 1.2 kHz for 1,4-C&D* and 192.4 + 1.2 kHz for 1,3,5-CsH,D,. Liquid crystal measurements were also published for pyridine in the ortho position 184.2 ? 1.2 kHz (14) and 183 ? 1 kHz (IS), in the meta position 187.3 -c 1.2 kHz (14) and 185 + 1 kHz (15), and finally in the para position 185.7 + 1 kHz (15) and 188 f 6 kHz (15). There exists only for the paru position a gas-phase value of 196 -C4 kHz (Heineking el al. (16)). As already mentioned we cannot compare these values directly to the calculated ones but at least they show similar trends. From previous comparisons we estimate the absolute error in our calculations to be less than 10 kHz and the relative error less than 1 kHz. The values are close to the Hartree-Fock limit. An analysis of the values in Table I shows that the couplings in the higher azines are additive in increments gained from the shifts in pyridine relative to benzene. Slightly better values obtained from a regression are given in Table II. If these increments are added to the values of benzene (194.0, -9 1.O, and - 103.0 kHz, respectively) the couplings can be predicted with an nns deviation of 0.34 kHz. For s-triazine. e.g., we have to add two ortho increments and one para increment, which yield the values 184.6 (XX), -91 .O (~JJ) and -93.6 (zz) kHz compared to the SCF values of 184.8, -91.0, and -93.8 kHz. Such an additivity is also found for charge orders (in HMO or CNDO calculations) and might not be very surprising. Nevertheless, we think that it may give some orientation to classify experimental values. Although obtained for a constant D-C bond length the values in Table I will be pretty accurate predictions for the class of azines as soon as they can be hooked to an accepted experimental value of one of the compounds. as the few D-C (or better H-C) bond lengths known accurately in these compounds show only small changes. ACKNOWLEDGMENT We are grateful to the CIBA-Stiftung for their financial support of this work. REFERENCES 1. H. HUBER, J. Chem. Phys. 83,4591-4598 (1985). 2. S. GERBERAND H. HUBER, J. Mol. Spectrosc. 134, 168-l 75 ( 1989). 3. R. M. STEVENS,E. SWITKES,E. A. LAWS, AND W. N. LIPSCOMB,J. Amer. Chem. Sot. 93,2603-2609 (1971). 4. F. MATA, M. J. QUINTANA, AND G. 0. SORENSEN,J. Mol. Struct. 42, l-5 ( 1977). 5. W. WERNER, H. DREIZLER,AND H. D. RUDOLF, 2. Naturforsch. A 22, 531-543 (1967); A. ALMENNINGEN,G. BJOERNSEN, T. O~ERSEN, R. SEIP,AND T. G. STRAND,Acta Chem. &and. Ser. A 31, 63-68 (1977).
NOTES 6. 7. 8. 9. 10.
11. 12. 13. 14. 15. 16.
317
L. FERNHOLTAND C. ~MMING, Acta Chem. Stand. Ser. A 32,271-273 (1978). B. J. M. B~RMANS,G. DE WITH, AND F. C. MIJLHOFF,.I. Mol. Struct. 42, 12 I-128 ( 1977). J. E. LANCASTERAND B. P. STOICHEFF. Cunad. J. Phys. 34, 1016-1021 (1956). V. A. JOBAND K. K. INNES, J. Mol. Spectrosc. 71.299-311 ( 1978). P. C. M. VAN ZIJL,C. MACLEAN, C. SKOGLUND,AND A. A. BOTHNER-BY,J Mugn. Res. 65,316-325 (1985). M. OLDANI, T.-K. HA, AND A. BAUDER,Chem. Phys. Lett. 115, 317-320 (1985). S. JANS-BURL],M. OLDANI AND A. BAUDER,Mol. Phvs., submitted for publication. P. DIEHLAND M. REINHOLD,Mol. Phys. 36, 143-149 (1978). J. P. JACOBSEN AND E. J. PEDERSEN. J. Mugn. Res. 44, 101-108 ( 1981). R. AMBROSETTI, D. CATALANO,C. FORTE,AND C. A. VERACINI.Z. Naturforsch. A 41,43 l-435 ( 1986 ) N. HEINEKING,H. DREIZLER,AND R. SCHWARZ.Z. Naturforsch. .4 41, 1210-1213(1986). STEFANGERBER HANSPETERHUBER
Institute of Physical Chemistry Klingelbergstr. 80 4056 Basel, Switzerland Received June I9. I989
OF MOLECULAR
SPECTROSCOPY
Additivity in the Deuterium
138, 3 15-3 17 (1989)
Quadrupole
Coupling Constants
of Azines
A previously developed concept for the calculation of deuterium quadrupole coupling constants using basis sets of local high quality is applied to benzene and related azines. The deuterium quadrupole coupling constant is strongly correlated to the bond length, but in this work the bond length is kept constant to study the additional direct effects of the electronic structure changes in this class of compounds. It is found that the coupling constants of the higher azines can be ~1 ,989 Academic predicted by additive increments obtained from the couplings in pyridine. press. Inc.
As is well known the deuterium quadrupole coupling constants along the bond direction are strongly dependent on the bond length between deuterium and its neighbor. They can be well predicted with a relation given in previous papers ( 1, 2) taking into account the dependence on the bond length and applying an additional small empirical correction utilizing CNDO charge orders ( 1) or electronegativities (2). Here we investigate in more detail these second-order effects. For this purpose we keep the bond length between the deuterium and its neighbor as well as the type of neighboring atom constant and introduce nitrogen atoms in positions further away. This is performed on the following molecules: benzene, pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, and s-tetrazine. In most molecules there are several different positions resulting in 12 different couplings. The differences in the couplings are quite small (the full range being about 10 kHz) but as the compounds are very closely related, the differences in the calculated values are fairly accurate even if we apply only the SCF-level of approximation. The calculations were performed with the basis set given in Ref. ( 1). The concept of basis sets with local high quality allows one to calculate the couplings in these fairly large molecules with the same accuracy as in the smaller ones without prohibitively long computing times. The structure was taken from experiment except for the crucial bond length between the deuterium and its neighbor, which was kept constant at 108.5
TABLE I Calculated
Coupling
Tensors (in kHz, Conversion Factor 672.0 kHz/au). x is Along the Bond. y in the Plane, and z Vertical to the Plane of the Ring
Molecule
xx
Benzene
194.0
-91 .o
Pyridine-2-d,
-90.4
-99.9
-1.4
Pyridine-3-d,
190.3 192.8
-90.0
-102.8
0.2
Pyridine-4-d,
192.1
-92.1
-100.0
YY
zz
xY
-103.0
Pyridazine-3-d,
100.7
-89.4
-99.3
Pyridazine-4-d,
189.9
-91.1
-98.8
Pyrimidine-2-d,
167.0
-90.7
-96.2
Pyrimidine-4-d,
166.5
-91.4
-97.1
Pyrimidine-5-d,
191.7
-89.0
-102.6
Pyrazine
189.0
-89.2
-99.7
s-Triazine
184.8
-91 .o
-93.8
s-Tetrazine
183.2
-86.9
-96.3
4.6 -1.5 2.6 2.7
0022-2852/89 Copyright 0
$3.00
1989 by Academic Press, Inc.
All rights of reproduction in any form m.md
315
316
NOTES TABLE II
Increments for the o, m, and p Positions Relative to a Nitrogen, Obtained from a Linear Regression (in kHz, Conversion Factor 672.0 kHz/au) position
xx
YY
22
ortho
-3.65
0.53
3.13
meta para
-1.49 -2.07
1.20 -1.10
0.30 3.15
pm for reasons given above (for most azines this latter bond length is anyway not very accurately known experimentally). In detail the structures were taken from the following references: benzene (3), pyridine (4)) pyridazine (5), pyrimidine (6)) pyrazine ( 7)) s-triazine (8) and s-tetrazine ( 9). Table I lists the calculated coupling tensors. Although these values cannot be compared directly to experimental values as the crucial bond length is kept constant in the calculation, it may be of interest to give here a few experimental values available {all along the bond or the principal axes of the quadrupole coupling tensor). For benzene van Zijl et al. (10) have published a value of 240 k 20 kHz measured by NMR in the gas phase. This value seems to be far too high. For the same molecule M. Oldani et al. (1 I) determined the gas-phase value of 223 + 12 kHz, which has been corrected to 186.1 + 1.8 kHz in a molecular beam measurement ( 12). Liquid crystal measurements were given by Diehl and Reinhold ( 13) with 190.5 +_ 1.2 kHz for 1,4-C&D* and 192.4 + 1.2 kHz for 1,3,5-CsH,D,. Liquid crystal measurements were also published for pyridine in the ortho position 184.2 ? 1.2 kHz (14) and 183 ? 1 kHz (IS), in the meta position 187.3 -c 1.2 kHz (14) and 185 + 1 kHz (15), and finally in the para position 185.7 + 1 kHz (15) and 188 f 6 kHz (15). There exists only for the paru position a gas-phase value of 196 -C4 kHz (Heineking el al. (16)). As already mentioned we cannot compare these values directly to the calculated ones but at least they show similar trends. From previous comparisons we estimate the absolute error in our calculations to be less than 10 kHz and the relative error less than 1 kHz. The values are close to the Hartree-Fock limit. An analysis of the values in Table I shows that the couplings in the higher azines are additive in increments gained from the shifts in pyridine relative to benzene. Slightly better values obtained from a regression are given in Table II. If these increments are added to the values of benzene (194.0, -9 1.O, and - 103.0 kHz, respectively) the couplings can be predicted with an nns deviation of 0.34 kHz. For s-triazine. e.g., we have to add two ortho increments and one para increment, which yield the values 184.6 (XX), -91 .O (~JJ) and -93.6 (zz) kHz compared to the SCF values of 184.8, -91.0, and -93.8 kHz. Such an additivity is also found for charge orders (in HMO or CNDO calculations) and might not be very surprising. Nevertheless, we think that it may give some orientation to classify experimental values. Although obtained for a constant D-C bond length the values in Table I will be pretty accurate predictions for the class of azines as soon as they can be hooked to an accepted experimental value of one of the compounds. as the few D-C (or better H-C) bond lengths known accurately in these compounds show only small changes. ACKNOWLEDGMENT We are grateful to the CIBA-Stiftung for their financial support of this work. REFERENCES 1. H. HUBER, J. Chem. Phys. 83,4591-4598 (1985). 2. S. GERBERAND H. HUBER, J. Mol. Spectrosc. 134, 168-l 75 ( 1989). 3. R. M. STEVENS,E. SWITKES,E. A. LAWS, AND W. N. LIPSCOMB,J. Amer. Chem. Sot. 93,2603-2609 (1971). 4. F. MATA, M. J. QUINTANA, AND G. 0. SORENSEN,J. Mol. Struct. 42, l-5 ( 1977). 5. W. WERNER, H. DREIZLER,AND H. D. RUDOLF, 2. Naturforsch. A 22, 531-543 (1967); A. ALMENNINGEN,G. BJOERNSEN, T. O~ERSEN, R. SEIP,AND T. G. STRAND,Acta Chem. &and. Ser. A 31, 63-68 (1977).
NOTES 6. 7. 8. 9. 10.
11. 12. 13. 14. 15. 16.
317
L. FERNHOLTAND C. ~MMING, Acta Chem. Stand. Ser. A 32,271-273 (1978). B. J. M. B~RMANS,G. DE WITH, AND F. C. MIJLHOFF,.I. Mol. Struct. 42, 12 I-128 ( 1977). J. E. LANCASTERAND B. P. STOICHEFF. Cunad. J. Phys. 34, 1016-1021 (1956). V. A. JOBAND K. K. INNES, J. Mol. Spectrosc. 71.299-311 ( 1978). P. C. M. VAN ZIJL,C. MACLEAN, C. SKOGLUND,AND A. A. BOTHNER-BY,J Mugn. Res. 65,316-325 (1985). M. OLDANI, T.-K. HA, AND A. BAUDER,Chem. Phys. Lett. 115, 317-320 (1985). S. JANS-BURL],M. OLDANI AND A. BAUDER,Mol. Phvs., submitted for publication. P. DIEHLAND M. REINHOLD,Mol. Phys. 36, 143-149 (1978). J. P. JACOBSEN AND E. J. PEDERSEN. J. Mugn. Res. 44, 101-108 ( 1981). R. AMBROSETTI, D. CATALANO,C. FORTE,AND C. A. VERACINI.Z. Naturforsch. A 41,43 l-435 ( 1986 ) N. HEINEKING,H. DREIZLER,AND R. SCHWARZ.Z. Naturforsch. .4 41, 1210-1213(1986). STEFANGERBER HANSPETERHUBER
Institute of Physical Chemistry Klingelbergstr. 80 4056 Basel, Switzerland Received June I9. I989