Study of O─H···O Bonded Cyclic Trimer of (S)–(–)–1–Methyl–2–pyrrolidinemethanol by a Combined Spectroscopic and Computational Approach

Abstract

The O─H···O bonded cyclic trimer model for (S)–(–)–1–Methyl–2–pyrrolidinemethanol (MPM) has been proposed. Based on the experimental IR spectral features, a combined DFT and MD modeling techniques has been applied to obtain the most stable O─H···O bonded cyclic trimer. There are two measured electronic absorption bands at 292 and 329 nm in the UV–Vis region attributed to a self–induced aggregation with J–type alignment of the electronic transition dipole moments with head–to–tail interactions between the monomer species in the cyclic trimer in agreement with the MD simulations in solvent media. The cyclic trimer in chloroform predicted two bands at 242 and 249 nm and corresponds to the broad band at 292 nm. In the observed concentration–dependent ECD spectra, a band at 238 nm shifts to 245 nm with enhanced intensity by a factor of 3. These results establish the cyclic trimer as a basic supramolecular motif where cooperative O─H···O bonding and electron delocalization providing the stability for the trimer structure.