## 2 Results and Discussion
### LSD Analogues, the Applicability of the Results  
The methodology presented in the paper can be applied to similar compounds. It is important to \"mimic\" the experimental conditions throughout the theoretical calculations. For the optimization of the crystallographic structure, common functionals should be applied along with a reasonably large basis set. The IR spectrum should be calculated for an isolated molecule. The UV-VIS and NMR spectra prediction should be performed on structures optimized in a solvent. The practical application depends mainly on the available data for similar compounds. The obtained level of theory is examined on the LSD analogs in this section. In the paper by [PERSON] and coworkers [35], two d-Lysergic acid amides were synthesized, and the single crystal X-ray analysis determined their structure. These analogs differ from LSD in the size of the alkyl group of the amide part (analog 1 (**A1**)--2-pentyl, analog 2 (**A2**)--2-hexyl). The optimized structures of these compounds at the M05-2X/6-311++G(d,p) level of theory are presented in Figure 5, while their bond  
Figure 4: Optimized structures (at M05-2X/6-311++G(d,p) level of theory) of the most abundant fragments in the mass spectrum of LSD.  
lengths and angles are shown in Tables S4-S7. The MAE values for the bond lengths are 0.0176 **(A1)** and 0.0207 A **(A2)**. The bond angles were also well reproduced, with the MAEs equal to 0.83 **(A1)** and 1.08 **(A2)**. Low MAE values for the bond lengths and angles prove that the determined level of theory optimizes crystallographic structure adequately. The spectral characterization is expected to follow the previously discussed procedure, although \({}^{13}\)C NMR spectra were not provided.  
On the other hand, the \({}^{13}\)C NMR spectral prediction was performed for two commonly encountered analogs of LSD, namely 1-propionyl-d-lysergic acid diethylamide (**1P-LSD**) [8] and 1-butanol-d-lysergic acid diethylamide (**1B-LSD**) [29]. The experimental, unscaled, and scaled (by the previously determined factor of 0.848) theoretical chemical shifts are shown in Tables S8 and S9. Optimized structures of **1P-LSD** and **1B-LSD** are also presented in Figure 5. These results show a high correlation coefficient (0.999) between experimental and theoretical values in the case of both LSD analogs. The values of chemical shifts were overestimated with the MAE values of 15.7 (**1P-LSD**) and 14.7 (**1B-LSD**) ppm, similar to the results shown in Table 2. After the correction, the MAE values were lowered significantly to 2.5 (**1P-LSD**) and 2.4 (**1B-LSD**) ppm. The \({}^{13}\)C NMR spectra of these two analogs were similar to those of the LSD base. Propionyl group carbon atoms give rise to signals at 11.6 (CH\({}_{3}\)), 31.8 (CH\({}_{3}\)), and 170.3 (C=O) ppm in the theoretical spectrum. The significant difference in the theoretical chemical shift was calculated for C3 (LSD: 112.4 ppm and **1P-LSD**: 119.7 ppm) due to the presence of the propionyl group, which is consistent with the experimental results [8]. In the case of the butanoyl group, the chemical shifts in the theoretical spectrum are comparable to previously listed ones, 13.8 (CH\({}_{3}\)), 21.9 (CH\({}_{2}\)), 40 (CH\({}_{2}\)), and 169.3 (C=O) ppm. These results prove the assumption that the selected level  
Figure 5: Optimized structures (at M05-2X/6-311++G(d,p) level of theory) of several analogs of LSD.  
of theory, along with the correction factor, can be used to predict the \({}^{13}\)C NMR spectrum of novel LSD analogs.