Quantitative description of bond lengths alternation for caffeine−effects of ionization, proton-transfer, and noncovalent interaction

摘要: Abstract Effects of positive and negative ionization, deprotonation protonation, cationization with the simplest metal cation (Li+), hydrogen-bond formation acid (HF) on bond lengths alternation have been studied for psychoactive stimulant caffeine by quantum-chemical methods. For investigations, recently extended geometry-based HOMED (harmonic oscillator model electron delocalization) descriptor has applied to n-π π-π conjugated monocyclic bicyclic fragments caffeine. This structural index quantitatively describes variations delocalization when proceeding from neutral ionized, deprotonated, protonated, cationized, H-bonded forms. Ionization directly affects number electrons delocalized in cause greatest variations. Deprotonation protonation moderately change alternation. Noncovalent interactions, particular cationization, only slightly influence caffeine-aromaticity. Investigations H-bonding show additionally that favored basicity site is not always same this polyfunctional alkaloid.