Research article Received: 20 June 2014
Revised: 4 August 2014
Accepted: 7 August 2014
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/mrc.4139
Stereochemical behavior of geminal and vicinal 77Se–13C spin–spin coupling constants studied at the SOPPA(CC2) level taking into account relativistic corrections Yury Yu. Rusakov and Leonid B. Krivdin* A systematic theoretical study of geminal and vicinal 77Se–13C spin–spin coupling constants in the series of the open-chain selenides and selenium-containing heterocycles revealed that relativistic effects play an essential role in the selenium–carbon coupling mechanism, especially when the coupling pathway includes a triple bond, contributing to about 10–15% of their total values and noticeably improving the agreement of the calculated couplings with experiment. Both geminal and vicinal 77 Se–13C spin–spin coupling constants show marked stereochemical behavior as documented by their calculated dihedral angle dependence that could be used as a practical guide in stereochemical studies of organoselenium compounds. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: 77Se NMR; 77Se–13C spin–spin coupling constants; relativistic effects; SOPPA(CC2); open-chain selenides; seleniumcontaining heterocycles
Introduction
Results and Discussion
A good many of papers have been devoted to the stereochemical behavior of 77Se–1H spin–spin coupling constants providing a versatile tool in the stereochemical analysis of the organoselenium compounds, refer to review.[1] Indeed, it has been demonstrated that geminal and vicinal 77Se–1H couplings show a unique stereospecificity with respect to the orientational lone pair effect of selenium together with the geometry of a coupling pathway.[2] No such systematic study has been performed for the geminal and vicinal 77Se–13C spin–spin coupling constants, and present communication fills this gap. The stereochemical behavior of 77Se–1H together with 77Se–13C couplings is of utmost practical interest for the stereochemistry of organoselenium compounds[3] including biologically active selenosugars[4] as well as in view of a pure theoretical interest dealing with a classical semiempirical Karplus dependence,[5] recently revisited theoretically.[6] Also, it was a challenging task to perform the full four-component relativistic calculations of ‘real’ organoselenium compounds of up to 23 atoms including the fourthperiod selenium and to reveal the importance of relativistic corrections for geminal and vicinal 77Se–13C coupling constants. Relativistic effects play a major role in the mechanism of the nucleus spin–spin coupling involving at least one ‘heavy’ nuclei,[7] and we expected that relativistic corrections to 2J(Se,C) and 3J(Se,C) should be far from negligible based on our recent study of the relativistic effects in the one-bond 77Se–13C coupling constants that could result in a contribution of as much as 15–20% of the total values of 1J(Se,C) noticeably improving an agreement of the calculated couplings with their experimental values.[8]
Non-relativistic results
Magn. Reson. Chem. (2014)
Collected in Table 1 are the results of the present calculations of geminal and vicinal 77Se–13C spin–spin coupling constants performed in the series of diverse organoselenium compounds 1–9 in comparison with available experimental data for 1 and 2,[9] 3,[10] 4,[11] 5,[12] 6,[13] 7,[14] 8[15] and 9.[16] In our earlier publication[8] we have studied one-bond 77Se–13C coupling constants in a series of 13 organoselenium compounds including two compounds of the present series (compounds 7 and 9) at the nonrelativistic level using the second-order polarization propagator approach, SOPPA,[17] in combination with the second-order approximate coupled cluster model, SOPPA (CC2),[18] one from the most accurate pure nonempirical family of SOPPA-based methods used to calculate spin–spin coupling constants.[19] The same level of theory is used herewith for the nonrelativistic calculations of geminal and vicinal 77Se–13C spin– spin coupling constants in the present series of 1–9. Four basic Ramsey’s coupling contributions, namely, Fermi contact (FC), spin–dipolar (SD), diamagnetic spin–orbital (DSO), and paramagnetic SO (PSO) terms, were taken into account to contribute to the total values of 2J(Se,C) and 3J(Se,C). Traditionally for this
* Correspondence to: Leonid Krivdin, A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, 664033 Irkutsk, Russia. E-mail: [email protected] A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, 664033, Irkutsk, Russia
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc
Copyright © 2014 John Wiley & Sons, Ltd.
H
CH 3
C≡C
CH 2
Se
Se
H
CH 2
Formula
CH 3
3
3
6
J(Se,C ) 3 J(Se,C ) 3 5 J(Se,C )
2
2
J(Se,C ) J(Se,CH 3-ax) 2 J(Se,CH 3-eq)
2+3
J(Se,C)
2+3
J(Se,C sp)
2
J(Se,CH 2)
3
J(Se,CH 3)
3
J(Se,C)
2
2
J(Se,C-1) J(Se,C-2)
2
J(Se,C)
2
Spin–spin coupling constant
Af Af Af
Af Af Af
Ag
A
0.02 0.03 0.03
0.03 0.02 0.02
0.02
0.08
0.02
0.03 0.03 0.01 0.01
A B C D A
0.00
0.02 0.01 0.01 0.00
J DSO
Af
A B Ae Ae
Conformer
1.50 0.95 1.31
1.85 1.23 0.75
2.06
13.18
0.63
0.33 0.64 0.52 0.03
2.16
1.92 0.50 0.31 2.21
J PSO
0.79 0.05 0.27
0.39 0.12 0.15
3.13
0.90
1.32
0.27 0.40 0.01 0.07
0.28
0.03 0.07 0.14 0.34
J SD
b
All coupling constants, individual coupling contributions and relativistic corrections are in Hz. Relativistic corrections calculated at the DFT-PBE0 level, refer to text for details. c Conformationally averaged total SOPPA(CC2) values including relativistic corrections. d Taken from different sources,[9–16] refer to text for details. Signs in parentheses are assigned based on the present calculations. e Triply degenerated. f Doubly degenerated. g Conformationally rigid.
a
9
8
7
6
5
4
3
2
1
13
Se– C spin–spin coupling constants calculated in the series of 1–9 at the SOPPA(CC2) levela
77
Compound
Table 1.
31.16 0.37 9.46
0.87 5.98 18.40
3.32
16.11
4.16
12.46 4.56 3.31 8.13
11.71
0.34 21.96 28.24 0.68
J FC
30.47 1.4 11.01
3.08 4.65 17.52
2.27
28.47
6.09
12.37 4.29 2.79 8.18
9.83
2.31 21.38 27.80 1.87
J
1.83 0.34 0.63
1.05 0.46 1.47
1.81
9.13
0.40
0.3 0.92 0.1 0.2
0.91
1.12 2.73 3.14 1.26
ΔJ relb
32.30 1.74 11.64
4.13 5.11 18.99
4.08
37.6
5.69
12.07 5.21 2.69 8.38
8.92
3.43 24.11 30.94 3.13
J + ΔJ rel
32.30 1.74 11.64
4.13 12.05
4.08
37.6
5.69
4.33
8.92
8.23
3.46
J calcc
34.0 ( )2.7 11.9
( )3.1 13.7
( )5.7
( )36.3
5.9
5.6
9.7
10.7
4.1
J expd
Y. Y. Rusakov and L. B. Krivdin
Magn. Reson. Chem. (2014)
Stereochemical behavior of geminal and vicinal 77Se–13C spin–spin coupling constants
Figure 1. Equilibrium structures and conformational populations of the true-minimum conformers of 1–9 localized at the MP2/6-311G(d,p) level.
laboratory, the most reliable NMR-oriented Sauer’s basis set augcc-pVTZ-J of triple zeta quality with tight s-functions was used on coupled selenium[20] and carbon[21] atoms, while much more economical Dunning’s cc-pVDZ[22] of double zeta quality was used for the rest of molecules. In this paper, we did not consider either solvent effects or vibrational corrections that are expected to be fairly small as compared with stereoelectronic effects governing the stereochemical behavior of 2J(Se,C) and 3J(Se,C) under scrutiny. Rovibrational effects deserve special scrutiny and require an enormous amount of computations for the molecules of that size, even at the density functional theory (DFT) level.
2
Figure 2. Correlation plot of the conformationally averaged J(Se,C) and 3 J(Se,C) calculated in the series of 1–9 at the SOPPA(CC2) level without relativistic corrections versus experiment.
Magn. Reson. Chem. (2014)
Some of the studied compounds are conformationally labile existing in the equilibrium of several (from two through four) true-minimum conformers. All these conformers were searched for and localized on the potential energy surface and then confirmed by the vibrational harmonic frequency analysis at the second Møller–Plesset perturbation theory MP2/6-311G(d,p) level, and their populations given in Fig. 1 were found from the corresponding Boltzmann factors. Accordingly, all computed 2J(Se,C) and 3J(Se,C) in the conformationally labile compounds were conformationally averaged in accord with the corresponding conformational populations.
2
Figure 3. Correlation plot of the conformationally averaged J(Se,C) and 3 J(Se,C) calculated in the series of 1–9 at the SOPPA(CC2) level taking into account relativistic corrections versus experiment (best result).
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc
Y. Y. Rusakov and L. B. Krivdin Coming back to Table 1, it is seen that basically, the FC term dominates, but in many cases, it is critically small (
Revised: 4 August 2014
Accepted: 7 August 2014
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/mrc.4139
Stereochemical behavior of geminal and vicinal 77Se–13C spin–spin coupling constants studied at the SOPPA(CC2) level taking into account relativistic corrections Yury Yu. Rusakov and Leonid B. Krivdin* A systematic theoretical study of geminal and vicinal 77Se–13C spin–spin coupling constants in the series of the open-chain selenides and selenium-containing heterocycles revealed that relativistic effects play an essential role in the selenium–carbon coupling mechanism, especially when the coupling pathway includes a triple bond, contributing to about 10–15% of their total values and noticeably improving the agreement of the calculated couplings with experiment. Both geminal and vicinal 77 Se–13C spin–spin coupling constants show marked stereochemical behavior as documented by their calculated dihedral angle dependence that could be used as a practical guide in stereochemical studies of organoselenium compounds. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: 77Se NMR; 77Se–13C spin–spin coupling constants; relativistic effects; SOPPA(CC2); open-chain selenides; seleniumcontaining heterocycles
Introduction
Results and Discussion
A good many of papers have been devoted to the stereochemical behavior of 77Se–1H spin–spin coupling constants providing a versatile tool in the stereochemical analysis of the organoselenium compounds, refer to review.[1] Indeed, it has been demonstrated that geminal and vicinal 77Se–1H couplings show a unique stereospecificity with respect to the orientational lone pair effect of selenium together with the geometry of a coupling pathway.[2] No such systematic study has been performed for the geminal and vicinal 77Se–13C spin–spin coupling constants, and present communication fills this gap. The stereochemical behavior of 77Se–1H together with 77Se–13C couplings is of utmost practical interest for the stereochemistry of organoselenium compounds[3] including biologically active selenosugars[4] as well as in view of a pure theoretical interest dealing with a classical semiempirical Karplus dependence,[5] recently revisited theoretically.[6] Also, it was a challenging task to perform the full four-component relativistic calculations of ‘real’ organoselenium compounds of up to 23 atoms including the fourthperiod selenium and to reveal the importance of relativistic corrections for geminal and vicinal 77Se–13C coupling constants. Relativistic effects play a major role in the mechanism of the nucleus spin–spin coupling involving at least one ‘heavy’ nuclei,[7] and we expected that relativistic corrections to 2J(Se,C) and 3J(Se,C) should be far from negligible based on our recent study of the relativistic effects in the one-bond 77Se–13C coupling constants that could result in a contribution of as much as 15–20% of the total values of 1J(Se,C) noticeably improving an agreement of the calculated couplings with their experimental values.[8]
Non-relativistic results
Magn. Reson. Chem. (2014)
Collected in Table 1 are the results of the present calculations of geminal and vicinal 77Se–13C spin–spin coupling constants performed in the series of diverse organoselenium compounds 1–9 in comparison with available experimental data for 1 and 2,[9] 3,[10] 4,[11] 5,[12] 6,[13] 7,[14] 8[15] and 9.[16] In our earlier publication[8] we have studied one-bond 77Se–13C coupling constants in a series of 13 organoselenium compounds including two compounds of the present series (compounds 7 and 9) at the nonrelativistic level using the second-order polarization propagator approach, SOPPA,[17] in combination with the second-order approximate coupled cluster model, SOPPA (CC2),[18] one from the most accurate pure nonempirical family of SOPPA-based methods used to calculate spin–spin coupling constants.[19] The same level of theory is used herewith for the nonrelativistic calculations of geminal and vicinal 77Se–13C spin– spin coupling constants in the present series of 1–9. Four basic Ramsey’s coupling contributions, namely, Fermi contact (FC), spin–dipolar (SD), diamagnetic spin–orbital (DSO), and paramagnetic SO (PSO) terms, were taken into account to contribute to the total values of 2J(Se,C) and 3J(Se,C). Traditionally for this
* Correspondence to: Leonid Krivdin, A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, 664033 Irkutsk, Russia. E-mail: [email protected] A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, 664033, Irkutsk, Russia
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc
Copyright © 2014 John Wiley & Sons, Ltd.
H
CH 3
C≡C
CH 2
Se
Se
H
CH 2
Formula
CH 3
3
3
6
J(Se,C ) 3 J(Se,C ) 3 5 J(Se,C )
2
2
J(Se,C ) J(Se,CH 3-ax) 2 J(Se,CH 3-eq)
2+3
J(Se,C)
2+3
J(Se,C sp)
2
J(Se,CH 2)
3
J(Se,CH 3)
3
J(Se,C)
2
2
J(Se,C-1) J(Se,C-2)
2
J(Se,C)
2
Spin–spin coupling constant
Af Af Af
Af Af Af
Ag
A
0.02 0.03 0.03
0.03 0.02 0.02
0.02
0.08
0.02
0.03 0.03 0.01 0.01
A B C D A
0.00
0.02 0.01 0.01 0.00
J DSO
Af
A B Ae Ae
Conformer
1.50 0.95 1.31
1.85 1.23 0.75
2.06
13.18
0.63
0.33 0.64 0.52 0.03
2.16
1.92 0.50 0.31 2.21
J PSO
0.79 0.05 0.27
0.39 0.12 0.15
3.13
0.90
1.32
0.27 0.40 0.01 0.07
0.28
0.03 0.07 0.14 0.34
J SD
b
All coupling constants, individual coupling contributions and relativistic corrections are in Hz. Relativistic corrections calculated at the DFT-PBE0 level, refer to text for details. c Conformationally averaged total SOPPA(CC2) values including relativistic corrections. d Taken from different sources,[9–16] refer to text for details. Signs in parentheses are assigned based on the present calculations. e Triply degenerated. f Doubly degenerated. g Conformationally rigid.
a
9
8
7
6
5
4
3
2
1
13
Se– C spin–spin coupling constants calculated in the series of 1–9 at the SOPPA(CC2) levela
77
Compound
Table 1.
31.16 0.37 9.46
0.87 5.98 18.40
3.32
16.11
4.16
12.46 4.56 3.31 8.13
11.71
0.34 21.96 28.24 0.68
J FC
30.47 1.4 11.01
3.08 4.65 17.52
2.27
28.47
6.09
12.37 4.29 2.79 8.18
9.83
2.31 21.38 27.80 1.87
J
1.83 0.34 0.63
1.05 0.46 1.47
1.81
9.13
0.40
0.3 0.92 0.1 0.2
0.91
1.12 2.73 3.14 1.26
ΔJ relb
32.30 1.74 11.64
4.13 5.11 18.99
4.08
37.6
5.69
12.07 5.21 2.69 8.38
8.92
3.43 24.11 30.94 3.13
J + ΔJ rel
32.30 1.74 11.64
4.13 12.05
4.08
37.6
5.69
4.33
8.92
8.23
3.46
J calcc
34.0 ( )2.7 11.9
( )3.1 13.7
( )5.7
( )36.3
5.9
5.6
9.7
10.7
4.1
J expd
Y. Y. Rusakov and L. B. Krivdin
Magn. Reson. Chem. (2014)
Stereochemical behavior of geminal and vicinal 77Se–13C spin–spin coupling constants
Figure 1. Equilibrium structures and conformational populations of the true-minimum conformers of 1–9 localized at the MP2/6-311G(d,p) level.
laboratory, the most reliable NMR-oriented Sauer’s basis set augcc-pVTZ-J of triple zeta quality with tight s-functions was used on coupled selenium[20] and carbon[21] atoms, while much more economical Dunning’s cc-pVDZ[22] of double zeta quality was used for the rest of molecules. In this paper, we did not consider either solvent effects or vibrational corrections that are expected to be fairly small as compared with stereoelectronic effects governing the stereochemical behavior of 2J(Se,C) and 3J(Se,C) under scrutiny. Rovibrational effects deserve special scrutiny and require an enormous amount of computations for the molecules of that size, even at the density functional theory (DFT) level.
2
Figure 2. Correlation plot of the conformationally averaged J(Se,C) and 3 J(Se,C) calculated in the series of 1–9 at the SOPPA(CC2) level without relativistic corrections versus experiment.
Magn. Reson. Chem. (2014)
Some of the studied compounds are conformationally labile existing in the equilibrium of several (from two through four) true-minimum conformers. All these conformers were searched for and localized on the potential energy surface and then confirmed by the vibrational harmonic frequency analysis at the second Møller–Plesset perturbation theory MP2/6-311G(d,p) level, and their populations given in Fig. 1 were found from the corresponding Boltzmann factors. Accordingly, all computed 2J(Se,C) and 3J(Se,C) in the conformationally labile compounds were conformationally averaged in accord with the corresponding conformational populations.
2
Figure 3. Correlation plot of the conformationally averaged J(Se,C) and 3 J(Se,C) calculated in the series of 1–9 at the SOPPA(CC2) level taking into account relativistic corrections versus experiment (best result).
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc
Y. Y. Rusakov and L. B. Krivdin Coming back to Table 1, it is seen that basically, the FC term dominates, but in many cases, it is critically small (
