Do intramolecular halogen bonds exist? Ab initio calculations and crystal structures' evidences

Cl center dot center dot center dot O intramolecular contacts are analysed here. Hence the Cambridge Structural Database (CSD) search was performed to find five-membered Cl-C=C-C=O pseudo-rings closed through Cl center dot center dot center dot O intramolecular contacts. Such rings were analysed and it was found that some of Cl center dot center dot center dot O distances are smaller than the corresponding sum of van der Waals radii. Additionally ab initio MP2/6-311++G(d,p) calculations and AIM analyses were carried out here on 3-chloropropenal and its fluoro derivatives to deepen the nature of intramolecular Cl center dot center dot center dot O interactions, some of findings may indicate that they are attractive and stabilizing ones.