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.

H and 13 C NMR spectra were recorded on a Bruker DRX 500 instrument (BBO probe) at 500.13 and 125.76 MHz, respectively, in steps of 10 K between 210 and 280 K (15 mg of the base form in 600 L CDCl 3 ), between 180 and 280 K (10 mg of the hydrochloride in 600 L [d4]methanol), and 298 K. Temperature calibration was done with a methanol reference sample. 1 H NMR spectra were acquired using a spectral width of 12 kHz, an acquisition time of 5.5 s and 16 scans, zerofilled to 128 k datapoints (0.09 Hz per point) and processed with a 1 Hz exponential decay. 13 C NMR spectra were acquired using a spectral width of 30 kHz, an acquisition time of 1.1 s and 2048 scans in about 1h, zerofilled to 128 k datapoints (0.23 Hz per point) and also processed without apodization. Peaks were fitted to a Lorentzian lineshape using MestreNova 8.0.0 (MestreLab Research S.L.) To increase the signal-to-noise ratio for peaks broadened beyond 20 Hz, the 13 C NMR spectra were reprocessed with a 5 Hz exponential decay. 1 H-EXSY spectra were recorded on a TBI inverse probe at 210 K (both samples), 200 and 190 K (hydrochloride in methanol-d 4 ). The spectra were acquired using a spectral width of 4 kHz, 1024 x 512 complex time domain datapoints, a mixing period of 50 ms (additionally 200 ms at 190 K) and 8 scans in about 4.5 h. The spectra were zerofilled to 2048 x 2048 datapoints and processed with a shifted square sine bell apodization in both dimensions. Populations and exchange rates were obtained from diagonal-and crosspeak integrals using EXSYCalc (MestreLab Research S.L.).

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a b s t r a c tThe complete series of menthol isomers and their corresponding amino derivatives (base and protonated/HCl forms), were investigated using experimental and theoretical data. Our study focused on the conformational and configurational analysis, and revealed that experimental data should be used in combination with calculated data. Furthermore, even in the case of the highly studied member, menthol, discrepancies were found among previously published literature values. We show that the correct determination of the population mix is a must for the correct prediction of the absolute configuration (AC) of neoisomenthol. The neoiso forms are of special interest since a number of structural inconsistences can be found in the literature. We present a stringent proof of the AC of neoisomenthol based on literature information. To the best of our knowledge, the AC of neoisomenthylamine is for the first time shown using experimental and calculated optical rotation data. A correction of a series of publications containing an important error in the assignment of (þ)-menthylamine (correct: (þ)-neomenthylamine) is presented. With 26 data pairs (experimental versus calculated) of optical rotation values a regression is performed. The AC of all 12 compounds, even the most difficult neoiso forms, could be predicted correctly using experimental low-temperature NMR data. Furthermore, if only experimental data with an optical rotation outside the range of À10 < [a] > þ10 are used, all 12 compounds would have been correctly assigned without lowtemperature NMR data as restraints.