Evaluation of small Gaussian basis sets and analysis of substituent effects in monosubstituted benzenes and phenols

Assessing the Efficacy of Nonsteroidal Anti-Inflammatory Drugs Through the Quantum Computation of Molecular Ionization Energies

“…Inclusion of electron correlation through density functional theory substantially enhanced the statistical correlation between the IEs and the activities, especially when the IEs were estimated by Koopman's theorem. Previous studies, [2][3][4] performed before the development of modern density functional theory, examined the relation between IEs and activities by a simpler molecular orbital theory in a minimal basis set while a more recent study 5 computes IEs of larger NSAIDS by an empirical theory. The present work shows that (i) a significant statistical correlation between IE and activity persists when more accurate electronic structure methods, namely density functional theories, are employed, and (ii) the inclusion of electron correlation by the density functionals (B3LYP or PBEPBE) improves upon the statistical correlation obtained by the Hartree-Fock method.…”

“…Ionization energies were computed by two approaches: (i) Koopman's Theorem, which observes that the absolute value of the energy of the highest occupied molecular orbital (HOMO) is approximately equal to the ionization energy, and (ii) the difference (Δ E ) between the total energy of the molecule and the total energy of its corresponding anion, i.e., the energy difference due to removing an electron (a direct measure of the ionization energy). To facilitate comparison with earlier work of Mehler and Gerhards, − we use a common set of molecules and pharmacological data.…”

General and Theoretical Aspects of Phenols

“…A direct consequence of the lower stability of the meta-X-phenol ions is the higher IE a of the corresponding neutral molecules whereas the para-X-phenols, on the contrary, exhibit the smallest IE a . The IE a s of the series of mono-halophenols are evaluated as follows (bearing in mind that the relevant value for the parent phenol is actually 8.48 eV): The observed changes in both quantities could partly be rationalized in classical terms of electron-donating and electron-withdrawing effects 439,440 .…”

Substituent electronic descriptors for fast QSAR/QSPR

“…Therefore, there is a great demand to develop electronic descriptors that not only can be calculated with high level of accuracy and low computation times but also they can be tabulated for future works. In this context, theoretical chemists have used quantum chemical calculations to investigate the substituent effect on the electronic structures and chemical properties of a set of molecules with the same structural backbone [14][15][16][17][18][19][20][21][22][23][24]. Calculations have been made on the whole molecular structures and therefore the complexity and computation time are still the major problems.…”