text: Similar to hydrogen bonds, a C–H···O interaction involves interactions of dipoles and therefore has directionality. The directionality of a C–H···O interaction is usually defined by the angle α between the С, Н and О atoms, and the distance d between the O and C atoms. In a С–Н···О interaction, the angle α is in the range between 90 and 180°, and the distance d is usually smaller than 3.2 Å. Bond strength is less than 1 kcal/mol. In the case of aromatic C–H donors, C–H···O interactions are not linear due to influence of aromatic ring substituents near the interacting C-H group. If aromatic molecules involved in С–Н···О interaction belong to the group of  polycyclic aromatic hydrocarbons, the strength of C–H···O interactions increases with the number of aromatic rings.
  C–H···O interactions can be important in drug design, being present in structures of therapeutic proteins, and nucleic acids.  
  O-H···C and N-H···C type interactions could also play a significant role and were first analyzed in 1993.