Crystal and NMR analyses of four precursors of N-(2-pyridyl) thermolabile protecting group (TPG) were carried out. Two torsion angles have been identified as indicators that predict the molecules' thermolabile properties. Conformation that minimizes the N1C8 distance is crucial for thermocyclisation. Nucleophilicity of the pyridyl ring is the driving force for the reaction but it is insufficient for thermocyclisation which is dominated by the molecules' ability to adopt a favourable conformation. The pKa value was recorded for all analyzed N-(2-pyridyl)aminoethylalcohols. However, its effect is small in the determination of thermolability. Based on the analysis that we carried out, N-benzyl N-(2-pyridyl)aminoethyl was selected as a potential precursor of thermolabile carbonate of TPG.