EVALUATION OF SPIN-DIPOLE AND ORBITAL CONTRIBUTIONS

TO SPIN-SPIN COUPLING INVOLVING THE alp NUCLEUS

R. K. Safiullin, Yu. Yu. Samitov, and R. M. Aminova

UDC 538.27 +539.194

Because of the development of NMR spectroscopy with 13C, I~N, 15N, 170, 19F, 31p, and other nuclei, an evaluation of the spin-dipole and orbital contributions to indirect spin-spin coupling of nuclei of atoms of the second, third, and, in some cases, higher periods is of definite interest. In [1-4], spin-dipole and orbital contributions to spin-spin coupling constants of I~ 13C, 14N, and 19F nuclei were evaluated. For the spin-spin coupling constants IJ13c_i3 C, ~J13c_14 N,

IJl4N_14N, iJl3c_lgF, iJ10B_19 F and iJl~N_19 F, it was shown that the spin-dipole

and orbital contributions are only an insignificant part in comparison with the Fermi contact contribution. These contributions are less than 25% for the con- stant IJ13c_19 F and less than 16% for the remaining spin-spin coupling constants

IJx_F, while for the constants IJIgF_IgF, 2JIgF_C_IgF, 2JIgF_B_19 F and 2jIgF_N_

19 F they were found to be predominant and very large in absolute value (of the

order of hundreds of Hz for IJigF_19 F and of the order of tens of Hz for 2JIgF_

i g F ) .

For contributions to spin-spin coupling constants involving nuclei of atoms of the third and higher periods, we used the MO LCAO method in [5] to obtain equations making it possible to evaluate them numerically. The equations are easy to program, and, when a set of orbital energies and corresponding molecular

TABLE i. Spin-Dipole, Orbital, and Contact Contri- butions to Spin-Spin Coupling Constants (SSCC), Hz

Spin- I Orbital Contact con- Type of SSCC Molecule dl~ole con- contribution tribution

tnbution

tJ~C__S, p

tj31p_~6cl

:~J,ac_17 0

zJ~O_abCl

CH3PH2

(CHa)2PH (CH3)3PO CHaP (O) C12

(CHa)3PO

CH3P (O) C12

CHsP(O) Ct2

(CHa)3PO

CH3P(O)CI2

0,11 (a) 0,14 (b)

0,05 (a) --0,06 (b)

0,03 (0 0,03 (b)

--0,17 (a) +0,10 (b) --0,21 (a) --0,07 (b)

0,01 (a) 0,01 (b)

--0,01 (a) +0,04 (b)

+0,03 (b)

--0,29 (a) --0,47 (b)

--0,35 (a) --0,12 (b) --0,27 (a) --0,68 (b)

--0,51 (a) --0,38 (b) --0,41 (a) --0,72 (b)

--0,25 (a) o,oo (b)

--0,09 (a) --0,11 (b)

--O, lO (b)

+24,65 (b)

+65,12 (b)

+86,29 (b)

--58,04 (b)

--79,84 (b)

+2,55 O)

Kazan State University. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. I0, No. 6, pp. 828-829, November-December, 1974. Original article submitted December 24, 1973.

�9 76 Plenum Publishing Corporation, 22 7 West 17th Street, New York, N. Y. 10011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $15.00.

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orbitals is available, the calculation time on an M-220 computer does not exceed 2.5 min. The results of calculations carried out in CNDO/SP (a) [6] and extended H~ckel method (b) approximations for CH3PH2, (CH3)2PH, (CH3)3PO, and CH3P(O)CI2 molecules are given in Table I.

It should be noted that the experimentally measured value of the spin-spin coupling constant 1J13c_31p in the compound CH3P(O)CI2 was found to be +104 Hz

[7]. On the basis of the data of Table I, it can be concluded that the spin-di- pole and orbital contributions to indirect spin-spin coupling involving nuclei of third-period atoms in the extended H~ckel method and CNDO/SP approximations are infinitesimal. An argument in favor of such an evaluation is the fact that both these contributions in the approximations are proportional to the value of yAYB <r-3>A~r-a>B, where the average values of (r-3> are taken according to the 2p valence orbitals for second-period atoms and according to 3p and 3d orbitals for third-period atoms. Therefore, the proportionality coefficient, for example, for F-F coupling exceeds the proportionality coefficients for P-C, P-O, P-C1, P-P, 0-0, O-C, and C-C coupling 800, -520, 4700, 2230, 120, -190, and 290 times, re- spectively. It is evident that for quantitative evaluation of the spin-dipole and orbital contributions to the spin-spin coupling constants involving nuclei of atoms of the third and higher periods, it is also necessary to take into account the inner 2p orbitals, i.e., to use the extended basis of the atomic orbitals. In this case, in the obtained equations, the values of (r-3>3p should be replaced

by those of <r-3~2p.

From a comparison of our calculated contributions to the enumerated spin- spin coupling constants and the experimental data given in [7], it is evident that the spin-spin coupling of P-C, P-O, P-P, and P-C1 is mainly due to a contact Fermi mechanism.

The authors are very grateful to G. M. Zhidomirov and N. D. Chuvylkin for making it possible to carry out the calculation according to the CNDO/SP program.

LITERATURE CITED

I. H. Nakatsuji, K. Hirao, H. Kato, and T. Yonezawa, Chem. Phys. Lett., 6, 541 (1970).

2. A. C. Blizzard and D. P. Santry, Chem. Commun., 1085 (1970). 3. D. C. Towl and K. Schaumburg, Mol. Phys., 22, 49 (1971). 4. C. Barbier, H. Faucher, and G. Berthier, T~-eor. Chim. Acta, 2__1, 105 (1971). 5. R.K. Safiullin, Yu. Yu. Samitov, and R. M. Aminova, Collection of Graduate-

Student Papers, Kazan State University, Kazan (1974). 6. G. M. Zhidomirov and N. D. Chuvylkin, Chem. Phys. Lett., 14, 52 (1972); N. D.

Chuvylkin and G. M. Zhidomirov, Zh. Strukt. Khim., 14, 14~--(1973). 7. I. V. Zakharov, Candidate's Dissertation, Leningrad-~1973).

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