Hindered rotational barriers in conjugated donor–acceptor substituted systems: calculations vs. experiments

Mark Sigalov (1) , Vladimir Lokshin (2) , Nina Larina (2) , Vladimir Khodorkovsky (2)

1 BGU - Ben-Gurion University of the Negev
2 CINaM - Centre Interdisciplinaire de Nanoscience de Marseille

Quantum mechanical calculations of barriers to rotation within push-pull p-conjugated molecules involving strong electron donors (D) and acceptors (A) using the generally accepted approach fail to reproduce the experimental barriers determined by temperature-dependent NMR spectra. On the examples of seven derivatives of this type with substituents of varying electron donating and accepting strength, we find that determination of one of the rotational barriers, for instance, that of the acceptor substituent, requires not only the energy calculation of the respective transition state of this substituent, but also the transition state of the donor and the transition state involving both donor and acceptor substituents. Calculations of the rotation barriers using B3LYP and APFD functionals considering three transition states produce the results with mean absolute deviations from experimental 10 barriers of 0.28-0.19 kcal/mol depending on the basis set.

Domaines: Chimie théorique et/ou physique

Mark Sigalov, Vladimir Lokshin, Nina Larina, Vladimir Khodorkovsky. Hindered rotational barriers in conjugated donor–acceptor substituted systems: calculations vs. experiments. Physical Chemistry Chemical Physics, 2020, 22 (3), pp.1214-1221. ⟨10.1039/c9cp06234c⟩. ⟨hal-02909943⟩