Polymer Segments at the Folding Limit: Raman Scattering for the Diglyme Benchmark

Abstract

Methyl-capped polyethers model flexible polar polymer chains. Their intrinsic all-trans conformational preference gives way to folded conformations if the chain is sufficiently long. We find by Raman cryospectroscopy in the gas phase and quantum chemical calculations that diglyme still prefers the stretched state, although folded variants come very close in energy. Three-body dispersion correction or higher-order electron correlation is important to match experiments, despite the polar character of C-O bonds. This turns oligoglymes into challenging benchmark systems for a balanced description of intra-chain torsion and inter-segment van der Waals attraction.

2-Methoxyethanol: harmonic tricks, anharmonic challenges and chirality-sensitive chain aggregation

“…The torsional barriers around both C-O single bonds are sufficiently low to be overcome during the expansion, but the OCCO torsional barrier is too high to be efficiently overcome in a jet expansion. 37,43,44 e.g., interconversion between gG 0 T and its enantiomer is hindered by a barrier in excess of 20 kJ mol À1 . Hence the initial population at room temperature is funnelled into a central T and a central G trapping basin by the cooling collisions and only the lowest conformation of each basin survives.…”