The Importance of Large-Amplitude Motions for the Interpretation of Mid-Infrared Vibrational Absorption and Circular Dichroism Spectra: 6,6′-Dibromo-[1,1′-binaphthalene]-2,2′-diol in Dimethyl Sulfoxide

Abstract

Using the 6,6'-dibromo-[1,1'-binaphthalene]-2,2'-diol molecule and its vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra measured in deuterated dimethyl sulfoxide as example, we present a first detailed study of the effects induced in VCD spectra by the large-amplitude motions of solvent molecules loosely bound to a solute molecule. We show that this type of perturbation can induce significant effects in the VA and VCD spectra. We also outline a computational procedure that can effectively model the effects induced in the spectra and at the same time provide detailed structural information regarding the relative orientations of moieties involved in a solute-solvent molecular complex.

Interplay of Exciton Coupling and Large‐Amplitude Motions in the Vibrational Circular Dichroism Spectrum of Dehydroquinidine

“…As can be seen, the Anti-Open and Syn-Open families contain nine conformers each (entries1-9 and1 0-18, respective- www.chemeurj.org ly), the Anti-Closed family contains eight conformers (19)(20)(21)(22)(23)(24)(25)(26), and the Syn-Closed family contains only four conformers (27)(28)(29)(30). The conformers in ag iven family can be grouped further into subfamilies, with the conformers in ag iven subfamily having very similarv alues for the t 1 and t 2 angles andd ifferent values for the t 3 and t 4 angles.…”

“…Our goal in this sectioni st os howt hat the presence/absence of the VCD excitonb ands in the simulated and/or experimental VCD spectra provides important insights into the conformational dynamics occurring in the experimental sample. We start by noting that among the 30 conformers considered, there are ten pairs of pseudo-conformers, that is, (1,3), (2,4), (14,16), (15,17), ( 19,21), (20,22), (23,25), ( 24,26), (27,29) and (28,30). As discussed in the previouss ection, and as can be seen in Ta ble 1, the structures of the pseudo-conformers in ap air differ mostly in the orientation of the hydroxyl group.…”

“…The strong exciton-coupling VCD bands are triggered by coupling of the transition dipole moments associated with the OÀHa nd CÀOb onds, and, as such, cannot occur in cinchonidine, which has no substituent on the quinoline and, thus, lacks the OCH 3 group. Besides providing ac leare xplanation for the contradictoryo bservation mentioned above,t his study provides furthere vidence [19][20][21] for the need to perform vibrational averaging of VCDs pectra.…”

Vibrational circular dichroism of a 2,5‐diketopiperazine (DKP) peptide: Evidence for dimer formation in cyclo LL or LD diphenylalanine in the solid state

“…15,16 Of special interest are the chiroptical methods like vibrational circular dichroism (VCD) [17][18][19][20][21][22] or Raman optical activity (ROA). [23][24][25] VCD is indeed very sensitive to minute conformational changes, 26,27 hence a very good probe of molecular conformation. 28,29 It has been widely applied to peptides, as a powerful tool for determining their secondary structure, in particular in the Amide I (C = O stretch) region.…”

Absolute Configuration Assignment of a Paraconic Acid Derivative via Vibrational Circular Dichroism Spectroscopy and Density Functional Theory Calculation

“…At the DFT level, the stability order and Boltzmann populations turn out to be different when relative equilibrium energies and relative free energies are compared. Since a more refined treatment was clearly outside the scope of the present work, we decided to carry on discarding relative free energies and corresponding Boltzmann populations, as they could be seriously affected by errors due to the large amplitude of the vibrational modes of compound 2a . Then, considering the relative energies for the equilibrium geometries, as reported in the last two columns of Table , where, for the sake of clarity, only conformers with a population factor larger than 1% have been collected, it can be appreciated that the MM rotamer 5 provides the most stable B97‐D/TZ2P conformer and that only the most stable eight conformers provided 87% of the total population.…”