Combined Experimental and Quantum Chemical Investigation of Chiroptical Properties of Nicotinamide Derivatives with and without Intramolecular Cation−π Interactions

Abstract

The circular dichroism (CD) spectra of neutral and cationic nicotinamide derivatives were experimentally examined in solution and in the solid state to show dramatic differences in the two phases and appreciable dependence on temperature and solvent. The CD spectrum of neutral nicotinamide 1 in solution was reproduced theoretically by averaging the theoretical spectra calculated for all of the extended and folded conformers (s-trans-G(+), s-cis-G(+), s-trans-T, and s-cis-T) weighted by their population. The preference for the folded, over the extended, conformers in less polar solvent was indicated by the calculation and confirmed experimentally by the analysis of specific rotations. Theoretical CD spectrum calculated for the conformer found in the X-ray structural analysis (s-cis-T) well reproduced the experimental CD spectrum measured in the solid state. Introducing cation-pi interactions by N-methylation of 1 to give 1-Me(+) led to dramatic changes in CD spectrum. Nevertheless, the experimental CD spectrum of 1-Me(+) was well reproduced by averaging the theoretical spectra calculated for a pair of most stable conformers (s-cis-G(+) and s-trans-G(+)) of 1-Me(+). The CD spectrum calculated for the s-trans-G(+) conformer, which was found in the X-ray crystallographic analysis, did not agree with the experimental one. The theoretical spectra were better reproduced in general by the more sophisticated RI-CC2 method, but the conventional TD-DFT method also gave acceptable results. This allowed us to successfully calculate the larger derivative 2-Me(+), for which the RI-CC2 method was not practically applicable. These results show that the structure/conformation may vary with the conditions employed (e.g., by altering the solvent or phase) and thus the experimental analysis under the identical condition is essential for a serious structural study. The present study on a series of nicotinamide derivatives 1, 1-Me(+), and 2-Me(+) with and without cation-pi interactions demonstrates that the combination of experimental and theoretical chiroptical methods is capable of providing reliable structural/conformational information in solution phase, which is complementary to the X-ray crystallographic structure in the solid state.

Issue Information

“…In addition, we found that when one of the terminal benzene moiety was kept at a fixed angle of 52° and the other was rotated, it was possible to reach the minimal barrier (14.3 kcal mol −1 ) for the conformation transfer. Under these conditions, the potential energy can be plotted as a function of the single dihedral angle and additionally according to the energy level a Boltzmann distribution at 25 °C can be obtained (see Figure S1 in the Supporting Information) 60. In agreement with the crystal measurements, 80 % of free molecules take the chair conformation at 25 °C, and in comparison the population of the boat conformer is less than 5 %.…”

Hydride ion-carrier ability in Rh(i) complexes of a nicotinamide-functionalised N-heterocyclic carbene ligand

“…E p -E p/2 (Fc/Fc + ) = 70 mV (theoretically E p -E p/2 is 59/n mV where n is the number of electrons transferred in the redox reaction)] and peak current [almost 3¥ that for the Fc/Fc + couple at the same concentration (i p scales with n 3/2 )] are indicative of a two-electron reduction, and consistent with the formal addition of hydride ion to the nicotinamide cation ring, eqn (1). [13][14][15][16][17] The return sweep shows a broad peak at +0.51 V for re-oxidation of the dihydronicotinamide reduction product, i.e. the reverse of eqn (1).…”

“…Electrocatalysis of hydrogen evolution is a characteristic of NAD + /H models. [13][14][15][16][17] The CVs of 1 to positive potentials are considerably complicated by oxidation processes arising from the dissociation of the iodide ion (see the ESI †). The electronic spectrum of 2 in the visible region is dominated by an interesting broad band centred at 466 nm (1650 M -1 cm -1 ).…”

Experimental and theoretical investigations of circular dichroism of donor–acceptor 1,1′‐binaphthyls: Influence of substitution on the coupling amplitude and cotton effect of the charge‐transfer band

“…The spectra were shifted by 0.1 eV to better match with the experimental main‐band couplet. Further computational details are found elsewhere 33, 34…”