Exploring Cyclopentadienone Antiaromaticity: Charge Density Studies of Various Tetracyclones

A systematic study of six tetracyclones
has been carried out using
experimental and theoretical charge density analysis. A three pronged
approach based on quantum theory of atoms in molecules (QTAIM), nucleus
independent chemical shifts (NICS) criterion, and source function
(SF) contributions has been performed to establish the degree of antiaromaticity
of the central five-membered ring in all the derivatives. Electrostatic
potentials mapped on the isodensity surface show that electron withdrawing
substituents turn both C and O atoms of the carbonyl group more electropositive
while retaining the direction of polarity.