Pan-Pan Zhou

Halogen as halogen-bonding donor and hydrogen-bonding acceptor simultaneously in ring-shaped H3N·X(Y)·HF (X = Cl, Br and Y = F, Cl, Br) Complexes

A series of ring-shaped molecular complexes formed by H(3)N, HF and XY (X = Cl, Br and Y = F, Cl, Br) have been investigated at the MP2/aug-cc-pVTZ level of theory. Their optimized geometry, stretching mode, and interaction energy have been obtained. We found that each complex possesses two red-shifted hydrogen bonds and one red-shifted halogen bond, and the two hydrogen bonds exhibit strong cooperative effects on the halogen bond. The cooperativity among the NH(3)···FH, FH···XY and H(3)N···XY interactions leads to the formations of these complexes. The AIM analysis has been performed at the CCSD(T)/aug-cc-pVQZ level of theory to examine the topological characteristics at the bond critical point and at the ring critical point, confirming the coexistence of the two hydrogen bonds and one halogen bond for each complex. The NBO analysis carried out at the B3LYP/aug-cc-pVTZ level of theory demonstrates the effects of hyperconjugation, hybridization, and polarization coming into play during the hydrogen and halogen bonding formations processes, based on which a clockwise loop of charge transfer was discovered. The molecular electrostatic potential has been employed to explore the formation mechanisms of these molecular complexes.

Information Functional Theory: Electronic Properties as Functionals of Information for Atoms and Molecules.

How to accurately predict electronic properties of a Columbic system with the electron density obtained from experiments such as X-ray crystallography is still an unresolved problem. The information-theoretic approach recently developed in the framework of density functional reactivity theory is one of the efforts to address the issue. In this work, using 27 atoms and 41 molecules as illustrative examples, we present a study to demonstrate that one is able to satisfactorily describe such electronic properties as the total energy and its components with information-theoretic quantities like Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy, and Onicescu information energy. Closely related to the earlier attempt of expanding density functionals using simple homogeneous functionals, this work not only confirms Nagys proof that Shannon entropy alone should contain all the information needed to adequately describe an electronic system but also provides a feasible pathway to map the relationship between the experimentally available electron density and various electronic properties for Columbic systems such as atoms and molecules. Extensions to other electronic properties are straightforward.

Physisorption of benzene derivatives on graphene: critical roles of steric and stereoelectronic effects of the substituent

A series of benzene derivatives with different substituents adsorbed on graphene was investigated using a density-functional tight-binding method with a dispersion correction. Compared to benzene, the derivative with either an electron-withdrawing or -donating substituent exhibits stronger physisorption. Moreover, the steric size of the substituent is important in determining the adsorption strength, while the direction and the number of H atoms in the substituent affect the electron transfer from graphene. NBO analysis reveals that the stereoelectronic effect of the conjugation between the substituent and the benzene ring strongly influences the π···π interaction region between the molecule and graphene. The findings can deepen the understanding of the interaction between an aromatic molecule and graphene as well as the corresponding adsorption mechanism.

Quantification of hyperconjugative effect on the proton donor X–H bond length changes in the red- and blueshifted hydrogen-bonded complexes

A whole dataset containing 55 hydrogen bonds were studied at the MP2/aug-cc-pVTZ level of theory. The changes of geometries and stretching vibrational frequencies show that there are 31 redshifted and 24 blueshifted hydrogen-bonded complexes. Natural bond orbital analysis was carried out at the B3LYP/aug-cc-pVTZ level of theory to obtain the electron densities in the bonding and antibonding orbitals of the proton donor X-H bond, which are closely associated with its bond length. Based on their relationship, a generally applicable method considering both the electron densities in the bonding and antibonding orbitals of the proton donor X-H bond has been developed to quantitatively describe the hyperconjugative effect on the X-H bond length changes in these hydrogen-bonded complexes.

Electronic origin of pyridinyl N as a better hydrogen-bonding acceptor than carbonyl O

A diarylamine compound, 2-(phenylamino)nicotinic acid, can form either the carboxyl acid–acid dimer or acid–pyridine chain in its polymorphic structures. Quantum mechanical calculations indicate that the hydrogen-bonding strength of the heterosynthon is stronger. Conceptual density functional theory is then used to understand the fundamental cause of pyridine N being a better hydrogen-bonding acceptor.

T-shaped phenol-benzene complexation driven by pi-involved noncovalent interactions

Abstract Intermolecular interactions between phenol and benzene molecules with the T-shaped geometries could be diverse. They can be pursued via two structural series: one with benzene standing above phenol using one or two C–H bonds as the anchoring point and the other with phenol standing on top of benzene with either C–H or O–H bond as the leg. In this work, structure and interaction properties of these species are investigated at the DFT M06-2X/6-311++G(2d,2p) level of theory without and with the counterpoise correction. A total of twelve distinct isomers have been identified, eight of which were unveiled for the first time. It is found that π–π interactions play essential roles in stabilizing these conformations, while C–H/π, C–H···O van der Waals interactions, and C–H···O and O–H/π hydrogen bonds are also involved and positively contribute to the stability of these species. Our energy decomposition analysis shows that the driving force for the formation of these complexes arises from attractive electrostatic, exchange, polarization, and dispersion terms, balanced by the repulsion term. The dispersion effect plays a dominant role, but the electrostatic and exchange terms are also markedly significant. Their close relationships between one another have also been disclosed.

Chiral bisoxazoline catalyzed decarboxylative aldol reactions between β-carbonyl acids and trifluoroacetaldehyde hemiacetals as well as trifluoroacetaldehyde: the mechanism, the origin of enantioselectivity and the role of a catalyst

Chiral bisoxazoline can catalyze the decarboxylative aldol reactions between β-carbonyl acids and trifluoroacetaldehyde hemiacetals as well as trifluoroacetaldehyde but with quite different enantioselectivities, in which the reaction involving trifluoroacetaldehyde hemiacetal results in excellent enantioselectivity (95% ee) while that involving trifluoroacetaldehyde results in poor enantioselectivity (28% ee). To uncover their differences, quantum mechanical calculations together with theoretical methods of global reactivity indexes, QTAIM, NCI and distortion/interaction models were applied to these two reactions; the reaction mechanism, the origin of enantioselectivity and the role of bisoxazoline were investigated in detail. For the reaction with 95% ee, it undergoes the processes of decomposition of trifluoroacetaldehyde hemiacetal, nucleophilic addition, decarboxylation and enol–keto tautomerization of the product, and the nucleophilic addition is the rate- and stereo-determining step. Both the distortion energy and weak intermolecular interactions are responsible for the enantioselectivity. For the reaction with 28% ee, it goes through the processes of nucleophilic addition, decarboxylation and enol–keto tautomerization of the product. Chiral bisoxazoline plays a crucial role in increasing the nucleophilicity of β-carbonyl acid in the reaction leading to 95% ee, while such a role is not observed in the reaction resulting in 28% ee. The calculated ee values are in good agreement with the experimental results. The results shown here will provide valuable insights into the understanding of these types of reactions, the design of highly efficient organocatalysts, and related asymmetric reactions.