Electric field effect on 31P NMR magnetic shielding

Magnetic shielding depends on molecular structure and noncovalent interactions. This study shows that it is also measurably dependent on the electric field generated by surrounding molecules. This effect has been observed explicitly for ³¹P nucleus using the adduct under field approach. The results obtained indicate that the field strength experienced by molecules in crystals consisting of molecules with large dipole moments is similar to that in polar solvents. Therefore, magnetic shielding should explicitly depend on solvent polarity. It is important to note that this effect cannot be reproduced correctly within the polarizable continuum model approach.

Tetravalent Oxygen and Sulphur Centres Mediated by Carborane Superacid: Theoretical Analysis

The tetravalent oxygen or sulphur centres, especially in H₄ O²⁺ and H₄ S²⁺ dications, were analysed experimentally and theoretically in various studies. Herein, we discuss stabilities of such centres in related H(CH₃ )₃ O²⁺ and H(CH₃ )₃ S²⁺ dications mediated by carborane superacid. The ωB97X-D/6-311++G(d,p) calculations were performed for a gas phase and for different solvents characterized by a wide range of dielectric constants for complexes of these dications with the conjugated base of H(CHB₁₁ F₁₁ ) carborane superacid, CHB₁₁ F₁₁ ^- , which indicate that these complexes are linked by hydrogen bonds. The Quantum Theory of 'Atoms in Molecules' (QTAIM) approach is applied to characterize these interactions. DFT results show that tetravalent oxygen and sulphur structures are additionally stabilized by polar solvents.

Solvent effects on acid-base complexes. What is more important: A macroscopic reaction field or solute-solvent interactions?

Can the geometry of an acid-base complex in solution be reproduced in calculations using an implicit accounting for the solvent effect in the form of a macroscopic reaction field? The answer is, "Yes, it can." Is this field equal to the real electric field experienced by the complex in solution? The answer is, "No, it is not." How can the geometry be correct under wrong conditions? This question is answered using density functional theory modeling of geometric and NMR parameters of pyridine⋯HF⋯(HCF₃)_n adducts in the absence and presence of an external electric field. This adduct under field approach shows that the N⋯H distance is a function of the H-F distance whatever method is used to change the geometry of the latter. An explicit account for solute-solvent interactions is required to get a realistic value of the solvent reaction field. Besides that, this approach reveals how certain NMR parameters depend on the solvent reaction field, the solute-solvent interactions, and the geometry of the N⋯H-F hydrogen bond. For some of them, the obtained dependences are far from self-evident.

Hydrogen bonds, and σ-hole and π-hole bonds – mechanisms protecting doublet and octet electron structures

For various interactions electron charge shifts try to protect the former doublet or octet electronic structure of the Lewis acid centre.

Negative hyperconjugation effect on the reactivity of phosphoramide mustard derivatives as a DNA alkylating agent: theoretical and experimental insights

In this work we suggest new factors affecting the reactivity of compounds similar to cyclophosphamide; as their reactivity mainly relies on the frontier molecular orbitals, the factors causing changes in the frontier molecular orbitals, alter the reactivity of these compounds too.