A joined theoretical–experimental investigation on the 1H and 13C NMR chemical shifts of chloro-alkenes

Density functional theory study of 13C NMR chemical shift of chlorinated compounds

“…Predictions based on the ab initio Hartree–Fock theory, second‐order Møller–Plesset theory, and density functional theories (DFTs) using different sizes of basis sets yielded good matching between experimental and computed values . Although second‐order Møller–Plesset theory provides excellent results, the DFT methods are more advantageous owing to their accuracy and low computational cost. These properties make DFT more practical and feasible for the computations of large molecules and databases containing a sizable number of molecules.…”

“…The approach is mostly used in cases where several heavy atoms are present [e.g., halomethyl cations CX 3 ‐ ( X = F, Cl, Br, I)]. Champagne et al also concluded that not only electron correlation but also relativistic SO effects have to be considered for computing Cl‐bonded carbons when making predictions for small chloroalkanes and chloroalkenes. Although their studies showed the necessity of adding relativistic SO correction and successfully evaluated the contribution by using quadratic response functions, the accuracy was not sufficient in all cases.…”

“…In Wiitala's optimization, the coefficients of the terms that intensively increase the chemical shift values were minimized in the definition, possibly leading to lower computed values compared with B3LYP. Furthermore, it is known that standard DFT leads to the overestimation of the paramagnetic contribution and to the underestimation of the shielding constants, especially in Cl‐bearing carbon nuclei. The prediction of chlorinated compounds often yields too high chemical shift values.…”

Fingerprints for Structural Defects in Poly(thienylene vinylene) (PTV): A Joint Theoretical–Experimental NMR Study on Model Molecules

“…As shown in recent works for other families of compounds, linear fits between the experimental and theoretical chemical shifts of simple compounds can be used to facilitate the interpretation of spectroscopic data of more complex systems. 39,44 So, in a preliminary step, the linear regression parameters were obtained from the NMR and theoretical data on a series of simple reference thiophene derivatives (2aÀ2h), and they were employed in a subsequent step to correct the calculated values for systematic errors.…”

“…For the PTV trimers, the B97-D/6-31G(d,p) method was used, since it includes a semiempirical treatment of the London dispersion forces. Then, the chemical shifts of all systems were obtained with the B3LYP functional and the 6-311+G(2d,p) basis set together with the GIAO method to ensure origin-independence, following the approach that was employed and tested recently for PVC oligomers 39,40 as well as fluoroionophores. 41,42 No attempt to use the B97-D XC functional for calculating the NMR chemical shift has been made, since there is no reason to believe it would improve over B3LYP and it is beyond the scope of this paper to assess its reliability.…”