Model molecules to classify CH⋯O hydrogen-bonds

We developed a set of conformationally locked molecules each of which makes a single CH⋯O H-bond/short contact and has different electron density at the acceptor oxygen atom. The downfield shift of the ¹H NMR signals due to the hydrogen involved in the CH⋯O H-bond varied from 0.93–1.6 ppm, and the magnitude of Δδ is in correlation with the hybridization state of the acceptor oxygen and with the CH⋯O H-bond strengths quantified using a computational method.