Insights into the spontaneity of hydrogen bond formation between formic acid and phthalimide derivatives.

We evaluated a group of phthalimide derivatives, which comprise a convenient test set for the study of the multiple factors involved in the energetics of hydrogen bond formation. Accordingly, we carried out quantum chemical calculations on the hydrogen bonded complexes formed between a sample of phthalimide derivatives with formic acid with the intent of identifying the most important electronic and structural factors related to how their strength and spontaneity vary across the series. The geometries of all species considered were fully optimized at DFT B3LYP/6-31++G(d,p), RM1, RM1-DH2, and RM1-D3H4 level, followed by frequency calculations to determine their Gibbs free energies of hydrogen bond formation using Gaussian 2009 and MOPAC 2012.

Quantum molecular mechanics-a noniterative procedure for the fast ab Initio calculation of closed shell systems.

In this article, we advance the foundations of a strategy to develop a molecular mechanics method based not on classical mechanics and force fields but entirely on quantum mechanics and localized electron-pair orbitals, which we call quantum molecular mechanics (QMM). Accordingly, we introduce a new manner of calculating Hartree-Fock ab initio wavefunctions of closed shell systems based on variationally preoptimized nonorthogonal electron pair orbitals constructed by linear combinations of basis functions centered on the atoms. QMM is noniterative and requires only one extremely fast inversion of a single sparse matrix to arrive to the one-particle density matrix, to the electron density, and consequently, to the ab initio electrostatic potential around the molecular system, or cluster of molecules.