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

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.