Experimental and theoretical study of intramolecular O•••O interaction in structurally rigid β-keto carboxylic esters

Here we report the crystal structures of quinolone carboxylate and bisethoxycarbonylvinylaniline derivates containing an O center dot center dot center dot O distance shorter than the sum of their van der Waals radii, which can be ascribed to their steric demand per se, which provide unequivocal evidence of intramolecular 1,5-closed shell type interaction. Theoretical studies including Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analysis are employed to characterize the nature of the closed shell O center dot center dot center dot O interaction. We found that the lone pair electrons on the interacting oxygens undergo stabilization due to negative hyperconjugation and maintains the otherwise repulsive O center dot center dot center dot O close contact.