Stereochemical behavior of geminal and vicinal ⁷⁷Se–¹³C spin–spin coupling constants studied at the SOPPA(CC2) level taking into account relativistic corrections

Abstract

A systematic theoretical study of geminal and vicinal (77)Se-(13)C 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-(13)C 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.

New pecJ-n (n = 1, 2) Basis Sets for Selenium Atom Purposed for the Calculations of NMR Spin–Spin Coupling Constants Involving Selenium

“…It is worth mentioning once again that, in the current case, we considered only the FC terms of the selenium SSCCs. In this sense, it could be said that we have developed the pecJ-n basis sets for the FC-dominating selenium SSCCs, covering by that the majority of cases [32,47,48,50,112]. It is also very important that all exponents in all shells were varied during the optimization process, which is different from what was conducted in our first work on the PEC method [98], where for the nonhydrogen atoms of the second period, only the s-, d-, and f -shells were varied to converge the target FC term to the ideal value.…”

“…In this respect, a delicate approach is required for the calculation of the indirect nuclear spin-spin coupling constants (SSCCs) involving selenium [29][30][31][32] because the calculation of the SSCCs with heavy chalcogens from the fourth period and below, in general, represents a challenging task [33][34][35][36][37][38][39][40][41] due to the complexity of the electronic structure of such systems and the need to pay special attention to the relativistic effects [42][43][44][45]. Accurate computation of the selenium SSCCs covers a wide range of applicability, representing, in the first place, a powerful tool of the stereochemical studies of organoselenium compounds [46][47][48][49][50][51][52][53][54]. Indeed, it should be emphasized that Se-H and Se-C SSCCs manifest a pronounced stereochemical 2 of 18 behavior basically governed by the orientational lone-pair effect of selenium [48,55].…”

“…Accurate computation of the selenium SSCCs covers a wide range of applicability, representing, in the first place, a powerful tool of the stereochemical studies of organoselenium compounds [46][47][48][49][50][51][52][53][54]. Indeed, it should be emphasized that Se-H and Se-C SSCCs manifest a pronounced stereochemical 2 of 18 behavior basically governed by the orientational lone-pair effect of selenium [48,55]. For example, large and, in some cases, even dramatic differences between geminal and vicinal Se-H SSCCs involving diastereotopic protons allowed making unambiguous diastereotopic assignments of signals in the 77 Se-1 H HMBC spectra of the series of selenium-containing four-, five-, and six-membered heterocycles, including the derivatives of thiaselenetane, selenasilole, thiaselenole, thiaselenolane, and dihydrothiaselenine [54].…”

Quantum chemical calculations of77Se and125Te nuclear magnetic resonance spectral parameters and their structural applications

“…A systematic theoretical study of the relativistic effects on selenium SSCCs started from the series of works by Rusakov et al, [ 368,369 ] where the manifestation of relativistic effects was investigated on the example of 77 Se‐ 13 C SSCCs. In a previous work, [ 368 ] one‐bond 77 Se‐ 13 C SSCCs were calculated in the series of open‐chain selenides, MeSeH ( 51 ), SeMe 2 ( 52 ), i PrSeH ( 53 ), PhSeMe ( 54 ), several selenium heterocycles, 19 , 20 , 23 , 25 , and other compounds, shown in Chart 9.…”

“…The QC calculations of geminal and vicinal 77 Se– 13 C SSCCs in the series of the open‐chain selenides and selenium‐containing heterocycles were performed at SOPPA(CC2) level taking into account relativistic corrections evaluated at the four‐component DFT(PBE0) level in Rusakov and Krivdin. [ 369 ] Relativistic effects were shown to play an essential role in the selenium‐carbon coupling mechanism, especially when the coupling pathway includes a triple bond. In the latter case, the relativistic contributions were found to be of 10–15% of the total values of 77 Se– 13 C SSCCs and to noticeably improve the agreement of the calculated couplings with the experiment.…”