Normal halogen dependence of ¹³C NMR chemical shifts of halogenomethanes revisited at the four‐component relativistic level

Abstract

The 'Normal Halogen Dependence' of C NMR chemical shifts in the series of halogenomethanes is revisited at the four-component relativistic level. Calculations of C NMR chemical shifts of 70 halogenomethanes have been carried out at the density functional theory (DFT) and MP2 levels with taking into account relativistic effects using the four-component relativistic theory of Dirac-Coulomb within the different computational methods (4RPA, 4OPW91) and hybrid computational schemes (MP2 + 4RPA, MP2 + 4OPW91). The most efficient computational protocols are derived for practical purposes. Relativistic shielding effect reaches as much as several hundreds of ppm for heavy halogenomethanes, and to account for this effect in comparison with experiment at the qualitative level, relativistic Dyall's basis sets of triple-zeta quality or higher are to be used within the framework of the four-component relativistic theory taking into account solvent effects. Relativistic geometrical optimization (as compared with the non-relativistic level) is essential for the molecules containing at least two iodines at one carbon atom. Copyright © 2016 John Wiley & Sons, Ltd.

Relativistic heavy atom effect on 13C NMR chemical shifts initiated by adjacent multiple chalcogens

“…It is interesting to note that both curves on Figures and have rather less slope than the approximate curve of HALA effect on 13 C NMR shielding constants in halogenomethanes . Indeed, as was shown in the work by Samultsev et al ., the relativistic contribution to carbon shielding rapidly increases with the sum of the atomic numbers of substituents (Z) in the series of halogenomethanes, resulting in coefficients of 5.98·10 −5 at the third power of Z.…”

“…To the best of our knowledge, cumulative HALA effect on 13 C NMR chemical shifts was studied only for the case of heavy halogen surrounding . The approximate dependence of magnitude of the relativistic HALA effect on 13 C shielding constant on the sum of the atomic numbers of adjacent chalcogens (cumulative effect) is presented in the current study for the first time.…”

“…As was shown in that paper, [27] due to CDs chemical shifts of α-carbon nuclei commonly move to the higher fields with increasing atomic number of the adjacent chalcogen. Although the CDs obtained for chemical shifts of α-carbons were found to be much less pronounced than the "normal halogen dependences," [13][14][15][16][32][33][34][35] the chalcogen-initiated HALA effect on 13 C NMR chemical shifts is still very important issue to be thoroughly investigated. Moreover, the relativistic influence of several chalcogens, directly bonded with the spectator carbon, is one of the most interesting peculiarities of the HALA effect.…”

On the long‐range relativistic effects in the 15N NMR chemical shifts of halogenated azines

“…The so‐called “Normal Halogen Dependence” (NHD) for the chemical shifts of the NMR nuclei bound directly to halogens was established earlier in a number of papers (see, for example, a series of papers by Kaupp, Malkina et al and other authors) and revisited recently at the four‐component relativistic level for the shielding constants of the carbon nuclei in α and β positions to the heavy p‐elements of the 3–6 periods and for the classical halogenomethanes series . It is well known that due to NHD chemical shifts of carbon nuclei commonly move to higher fields with increasing atomic number of the adjacent halogen.…”

“…The so-called "Normal Halogen Dependence" (NHD) for the chemical shifts of the NMR nuclei bound directly to halogens was established earlier in a number of papers (see, for example, a series of papers by Kaupp, Malkina et al [1][2][3][4] and other authors [5][6][7] ) and revisited recently at the four-component relativistic level for the shielding constants of the carbon nuclei in α and β positions to the heavy p-elements of the 3-6 periods [8] and for the classical halogenomethanes series. [9] It is well known that due to NHD chemical shifts of carbon nuclei commonly move to higher fields with increasing atomic number of the adjacent halogen. These dependencies are well documented for a number of nuclei and are mainly attributed to the relativistic spin-orbital effects caused by the heavy halogens [10] arising as follows: the spin-orbit coupling mixes some triplet character into the closed-shell singlet ground state wave function and thereby spin-polarizes the density distribution in the core and valence shells of the heavy atom (for more details, see the substantial review by Kaupp [11] ).…”