## 2 Results and Discussion
### Experimental and Theoretical NMR Spectra  
The chemical characterization of compounds through NMR spectra is necessary for structure determination except for when single-crystal XRD measurements are available. Before calculating NMR spectra, optimizing the structure in a solvent used in the experiment is beneficial. Optimizing TMS in the selected model and predicting its NMR spectrum is essential, as the values are shown relative to this compound (analogous to experiments). The theoretical NMR spectra can be computed for any magnetically active nuclei, including \({}^{1}\)H, \({}^{13}\)C, \({}^{15}\)N, and \({}^{17}\)O. The \({}^{1}\)H NMR spectra comparison to theoretical spectra can be ambiguous because of the multiplet structure and second-order effects, mainly if the compound contains aromatic moieties, which is the case with LSD. \({}^{1}\)H NMR spectra can be well reproduced, such as in references [26; 27; 28], but in the following parts, only the \({}^{13}\)C NMR spectrum of LSD will be explained. The proton-decoupled, \({}^{13}\)C[\({}^{1}\)H], NMR spectrum is much easier to reproduce, as only singlets are observed. Table 2 presents experimental, unscaled, and scaled theoretical values of \({}^{13}\)C chemical shifts, relative to TMS of the LSD structure in chloroform. The atom numbering scheme follows Figure 1. The NMR spectrum was acquired, as explained in the Methodology section. The experimental and theoretical results can be compared by calculating the correlation coefficient (R) and MEA value. As can be seen in Table 2, there is a high correlation between experimental and calculated values of \({}^{13}\)C NMR with an MAE value of 14.9 ppm. The \({}^{13}\)C NMR chemical shifts are usually overestimated, and the correction factor should be calculated. The correction factor for the given set of values is 0.848, including the possible solvent effect and rotation of specific bonds. Scaled values of theoretical shifts have the same correlation coefficient as experimental ones. However, the MAE is lowered to 2.0 ppm, which could include the uncertainty due to the solvent, temperature, and concentration dependence. The applicability of this correlation coefficient is probed in the last part of the article for the LSD analogs. A detailed analysis of the positions is not necessary for the prediction. However, it can be beneficial, especially if different substituents are added to the psychoactive substance backbone, and their effects can be followed. The following paragraph outlines some of the prominent carbon positions. The lowest values of chemical shifts were obtained for the terminate carbon atoms in positions 22 and 24 (around 13 ppm in experimental and theoretical spectra). The chemical shift of C4 is reproduced within 0.5 ppm in the theoretical spectrum. CH2 group carbon atoms of diethylamine moiety have higher chemical shifts due to the proximity of nitrogen atoms (39 ppm on average). The same reason leads to the chemical shift of 42 ppm in the experimental and 39 ppm in the theoretical spectrum of the methyl group attached to a nitrogen atom. Carbon atoms in the aromatic core and parts with elongated delocalization have chemical shifts above 100 ppm in both spectra. Due to the similarity in the chemical shifts, the reproduction of this part can be difficult. However, in the case of LSD, the differences between the experiment and prediction were minimal. The highest chemical shift value was calculated for the carbonyl oxygen with a difference of 4 ppm. The same method is applied in this contribution to the LSD analogs to prove the applicability of the selected level of theory.