Influence of the external pressure on improper character of intramolecular C–H⋯O interactions

The ZZ conformer of 3-methylacrolein is chosen as a model molecule to study the influence of the external pressure on the C–H⋯O intramolecular improper interaction. The effect of the external pressure is modeled by embedding the molecule in helium clusters of variable size. The compression of the molecule encapsulated in the cluster follows from the valence repulsion forces exerted by the helium atoms. Calculations at the level of the MP2/cc-pVTZ approximation show that the improper, blue-shifting, character of the C–H⋯O intramolecular interaction is increased by the compression.