What is the driving force behind molecular triangles and their guests? A quantum chemical perspective about host–guest interactions

The physical nature of host–guest interactions occurring between molecular triangles and linear anions was explored using DFT calculations combined with energy decomposition analyses, nuclear independent chemical shift, and non-covalent interactions.

A theoretical study of the intramolecular proton transfer and calculation of the nucleus independent chemical shift in juglone and some of its derivatives

In the present study, first, the intramolecular proton transfer (IPT) process of juglone and its derivatives were theoretically investigated in the gas phase and the effect of electron-withdrawing and electronreleasing substituents in different positions of the phenyl and benzoquinone rings of juglone on the IPT process was studied in which the geometries, energies and thermodynamic functions of the compounds were obtained using DFT calculations at the B3LYP/6-31+G(2d,p) level. Next, the influence of IPT on changing the aromaticity of the phenyl and benzoquinone rings was investigated. To determine the aromaticity of the rings, nuclear independent chemical shift (NICS) values were calculated for the ground state and transition state structures (GS1,TS,GS2) using the continues set of gauge transformations (CSGT) procedure at the B3LYP/6-311+G(2d,p) level.

Ab initio studies on the aromaticity of mixed tetramer neutral clusters

Ab initio calculations were performed to asses the aromatic behavior of mixed tetramer neutral cluster (Be2N2, Be2P2, Mg2N2, Mg2P2). Harmonic vibrational analysis has been performed to ensure the stability of the optimized geometries. The analysis of structure, vibrational frequencies, and molecular orbitals indicates that all these tetramer favor planar atomic configuration as the lowest energy structure and exhibit the characteristics of aromaticity (planarity and two π- electrons in the delocalized molecular orbital). Other than this, the aromatic character of these clusters has been verified based on established criteria of aromaticity such as chemical (extra stability), and magnetic criteria i.e. by calculating Nuclear Independent Chemical Shift (NICS) at the ring centers. The extra electronic stability of these clusters towards donating or accepting of electrons is also reflected in the calculated large ionization potential and low electron affinity