Stereochemical analysis of (+)-limonene using theoretical and experimental NMR and chiroptical data

Abstract

a b s t r a c tUsing limonene as test molecule, the success and the limitations of three chiroptical methods (optical rotatory dispersion (ORD), electronic and vibrational circular dichroism, ECD and VCD) could be demonstrated. At quite low levels of theory (mpw1pw91/cc-pvdz, IEFPCM (integral equation formalism polarizable continuum model)) the experimental ORD values differ by less than 10 units from the calculated values. The modelling in the condensed phase still represents a challenge so that experimental NMR data were used to test for aggregation and solventesolute interactions. After establishing a reasonable structural model, only the ECD spectra prediction showed a decisive dependence on the basis set: only augmented (in the case of Dunning's basis sets) or diffuse (in the case of Pople's basis sets) basis sets predicted the position and shape of the ECD bands correctly. Based on these result we propose a procedure to assign the absolute configuration (AC) of an unknown compound using the comparison between experimental and calculated chiroptical data.

Good Computational Practice in the Assignment of Absolute Configurations by TDDFT Calculations of ECD Spectra

“…As for the basis set, we recommend Ahlrichs’ def2‐SVP or def2‐TZVP, or, more in general, basis sets of double or triple‐ζ quality with a sufficiently wide set of polarization functions. Diffuse functions may be necessary whenever Rydberg states contribute substantially to the ECD spectrum . The basis set convergence may be easily verified by using one of the two methods discussed in the paragraph “Choice of the TDDFT Basis Set” below.…”

“…Diffuse functions may be necessary whenever Rydberg states contribute substantially to the ECD spectrum. 37 The basis set convergence may be easily verified by using one of the two methods discussed in the paragraph "Choice of the TDDFT Basis Set" below. In general, the weaker the computed (and experimental) ECD spectrum, the stronger will be its dependence on the calculation method, including functional, basis set, input geometry, and solvation model.…”

Tempo-spatial chirogenesis. Limonene-induced mirror symmetry breaking of Si Si bond polymers during aggregation in chiral fluidic media

“…Firstly, the UV-vis and CD spectra of nBuPS aggregates produced in a mixture of [62]. Although vibrational circular dichroism (VCD) experiment followed by population analysis of neat (S)-limonene was not reported by the same research groups [62,63], these results prompted us to investigate the g abs value of nBuPS aggregates in detail. Noting that (R)-limonene is a naturally abundant terpene, while (S)-limonene is not.…”

“…Possibly, each dot weakly emits the CPL signal because of the CPL-active nBuPS aggregates. The g abs value of nBuPS aggregates vs (R)-and (S)-limonene fractions in tersolvents Recent knowledge and understanding of the conformational structure indicated that (R)-limonene mainly exists as a mixture of three stable rotational isomers with the quasi-equatorial orientation of the isopropenyl group on the cyclohexene ring[62,63]. Minor rotational isomers are three unstable isomers with the quasi-axial orientation of the isopropenyl group on the cyclohexene ring…”

Assigning the stereochemistry of syn and anti β-trimethylsiloxy-α-trimethylsilyl alkanoic acid silyl esters using GIAO 1H NMR chemical shift calculations

“…Since a few decades, ab initio NMR chemical shift calculations have been used to interpret experimental spectroscopic data and therefore to assign the structures, the stereostructures, as well as the conformations of complex molecules, including, to name a few, supramolecular host-guest compounds [1], elatenyne [2], eightmembered benzoannulated lactams [3], hexahydrobenzazocines [4], strychnine [5], heparin trisaccharide [6], triterpenes [7], dimeric indole alkaloids [8], thiazole and selenazole derivatives [9], (þ)-limonene [10], darcyribeirine [11]. This approach has also helped to analyze the signatures of stereochemistry in poly(vinyl chloride) (PVC) oligomers and to highlight the signatures of their unsaturated and branched defects [12,13].…”