Perlin- and Bohlmann-type effects in cyclohexylamine and 1-aminopiperidine derivatives

Spectroscopic phenomena, such as the Perlin effect observed in ¹J_CH coupling constants and the Bohlmann effect in C-H stretching within infrared spectra, provide valuable insights into quantum processes like hyperconjugation and serve as tools to evaluate the conformational properties of compounds. This study investigates a Bohlmann-type effect in the N-H vibrations of piperidines and the Perlin effect in cyclohexylamine and 1-aminopiperidine derivatives. While cyclohexylamine and methyl (cyclohexylamino)acetate display N-H stretching bands typical of amines, 1-aminopiperidine and methyl [(piperidin-1-yl)amino]acetate exhibit a pronounced red shift, which remains unaffected by weak intramolecular hydrogen bonding. The Perlin effect was also observed for the set of compounds studied. Although there is a relationship of this phenomenon with hyperconjugation, contributions from Lewis interactions are shown to be dominant, specifically the stronger steric interactions experienced by σ_CHeq with endocyclic σ_CC, while hyperconjugative interactions have an indirect effect and help modulate the magnitude of the effect. These findings underscore the utility of spectroscopic analysis in uncovering subtle yet significant interactions that govern molecular behavior, offering valuable insights for the nuanced control of molecular design.