*3.4. Computational Details*

Molecular mechanics calculations were performed using Macromodel [40] interfaced to the Maestro program [41]. All conformational searches used the MMFFs force field. Twenty-one conformers of **1-I** and six conformers of **1-II** within a relative energy of 2 kcal/mol were found. The geometries of these conformers were subsequently optimized at DFT level with the B3LYP functional and 6-31G(d) basis set using Jaguar [42]. Single point calculations in DMSO with the mPW1PW91 functional and the same basis set were employed using Jaguar [42] to provide the shielding constant of carbon and proton nuclei. Meanwhile, the same procedure was applied on tetramethylsilane (TMS). Final 1H and 13C chemical shifts were obtained as the results of the Boltzmann weighted average. The theoretical chemical shifts were calculated according to a below equation.

$$
\delta\_{\rm calc}^{\rm x} = \sigma\_{\rm TMS} - \sigma^{\rm x} \tag{1}
$$

where δ*<sup>x</sup> calc* is the calculated shift for nucleus *x* (in ppm); <sup>σ</sup>*<sup>x</sup>* is the shielding constant for nucleus *x*; σ*TMS* is the shielding constant for the carbon in TMS σ*TMS* = 194.6867 ppm and for the proton in TMS σ*TMS* = 32.0845 ppm.

Statistical parameters were used to quantify the agreement between experimental and calculated data:

