Weak Dispersive Interactions Research Articles

Low-temperature oxidation of methane mediated by Al-doped ZnO cluster and nanowire: a first-principles investigation.

First-principles calculations are performed to investigate the catalytic oxidation of methane by using N2O as an oxidizing agent over aluminum (Al)-doped Zn12O12 cluster and (Zn12O12)2 nanowire. The impact of Al impurity on the geometry, electronic structure, and surface reactivity of Zn12O12 and (Zn12O12)2 is thoroughly studied. Our study demonstrates that Al-doped ZnO systems have a better adsorption ability than the corresponding pristine counterparts. It is found that N2O molecule is initially decomposed on the Al site to provide the N2 molecule, and an Al-O intermediate which is an active species for the CH4 oxidation. The conversion of CH4 into CH3OH over AlZn11O12 and (AlZn11O12)2 requires an activation energy of 0.45 and 0.29eV, respectively, indicating it can be easily performed at normal temperatures. Besides, the overoxidation of methanol into formaldehyde cannot take place over the AlZn11O12 and (AlZn11O12)2, due to the high energy barrier needed to dissociate C-H bond of the CH3O intermediate. Dispersion-corrected density functional theory calculations were performed through GGA-PBE exchange-correlation functional combined with a numerical double-ζ plus polarization (DNP) basis set as implemented in DMol3. To include the relativistic effects of core electrons of Zn atoms, DFT-semicore pseudopotentials were adopted. The DFT + D scheme proposed by Grimme was used to involve weak dispersion interactions within the DFT calculations. The reaction energy paths were generated by the minimum energy path calculations using the NEB method.

Neighbor effect on conformational spaces of alanine residue in azapeptides

The conformational properties of Alanine (Ala) residue have been investigated to understand protein folding and develop force fields. In this work, we examined the neighbor effect on the conformational spaces of Ala residue using model azapeptides, Ac-Ala-azaGly-NHMe (3, AaG), and Ac-azaGly-Ala-NHMe (4, aGA1). Ramachandran energy maps were generated by scanning (φ, ψ) dihedral angles of the Ala residues in models with the fixed dihedral angles (φ = ±90°, ψ = ±0° or ±180°) of azaGly residue using LCgau-BOP and LCgau-BOP + LRD functionals in the gas and water phases. The integral-equation-formalism polarizable continuum model (IEF-PCM) and a solvation model density (SMD) were employed to mimic the solvation effect. The most favorable conformation of Ala residue in azapeptide models is found as the polyproline II (βP), inverse γ-turn (γ′), β-sheet (βS), right-handed helix (αR), or left-handed helix (αL) depending on the conformation of neighbor azaGly residue in isolated form. Solvation methods exhibit that the Ala residue favors the βP, δR, and αR conformations regardless of its position in azapeptides 3 and 4 in water. Azapeptide 5, Ac-azaGly-Ala-NH2 (aGA2), was synthesized to evaluate the theoretical results. The X-ray structure showed that azaGly residue adopts the polyproline II (βP) and Ala residue adopts the right-handed helical (αR) structure in aGA2. The conformational preferences of aGA2 and the dimer structure of aGA2 based on the X-ray structure were examined to assess the performance of DFT functionals. In addition, the local minima of azapeptide 6, Ac-Phe-azaGly-NH2 (FaG), were compared with the previous experimental results. SMD/LCgau-BOP + LRD methods agreed well with the reported experimental results. The results suggest the importance of weak dispersion interactions, neighbor effect, and solvent influence in the conformational preferences of Ala residue in model azapeptides.

Physicochemical properties, pharmacokinetic studies, DFT approach, and antioxidant activity of nitro and chloro indolinone derivatives.

The process of developing of new drugs is greatly hampered by their inadequate physicochemical, pharmacokinetic, and intrinsic characteristics. In this regard, the selected chloro indolinone, (Z)-6-chloro-3-(2-chlorobenzylidene)indolin-2-one (C1), and nitro indolinone, (Z)-6-chloro-3-(2-nitrobenzylidene)indolin-2-one (C2), were subjected to SwissADME and density function theory (DFT) analysis. For compounds C1 and C2, the BOILED-Egg pharmacokinetic model predicted intestinal absorption, blood-brain barrier (BBB) penetration, and p-glycoprotein interaction. According to the physicochemical analysis, C1 has exceptional drug-like characteristics suitable for oral absorption. Despite only being substrates for some of the major CYP 450 isoforms, compounds C1 and C2 were anticipated to have strong plasma protein binding and efficient distribution and block these isoforms. The DFT study using the B3LYP/6-311G(d,p) approach with implicit water effects was performed to assess the structural features, electronic properties, and global reactivity parameters (GRP) of C1 and C2. The DFT results provided further support for other studies, implying that C2 is more water-soluble than C1 and that both compounds can form hydrogen bonds and (weak) dispersion interactions with other molecules, such as solvents and biomolecules. Furthermore, the GRP study suggested that C1 should be more stable and less reactive than C2. A concentration-dependent 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging activity was shown by both C1 and C2. In brief, this finding has provided a strong foundation to explore further the therapeutic potential of these molecules against a variety of human disorders.

Mechanistic docking in terpene synthases using EnzyDock.

Terpene Synthases (TPS) catalyze the formation of multicyclic, complex terpenes and terpenoids from linear substrates. Molecular docking is an important research tool that can further our understanding of TPS multistep mechanisms and guide enzyme design. Standard docking programs are not well suited to tackle the unique challenges of TPS, like the many chemical steps which form multiple stereo-centers, the weak dispersion interactions between the isoprenoid chain and the hydrophobic region of the active site, description of carbocation intermediates, and finding mechanistically meaningful sets of docked poses. To address these and other unique challenges, we developed the multistate, multiscale docking program EnzyDock and used it to study many TPS and other enzymes. In this review we discuss the unique challenges of TPS, the special features of EnzyDock developed to address these challenges and demonstrate its successful use in ongoing research on the bacterial TPS CotB2.

C-H···π interactions disrupt electrostatic interactions between non-aqueous electrolytes to increase solubility.

Grid-scale energy storage applications, such as redox flow batteries, rely on the solubility of redox-active organic molecules. Although redox-active pyridiniums exhibit exceptional persistence in multiple redox states at low potentials (desirable properties for energy storage applications), their solubility in non-aqueous media remains low, and few practical molecular design strategies exist to improve solubility. Here we convey the extent to which discrete, attractive interactions between C-H groups and π electrons of an aromatic ring (C-H···π interactions) can describe the solubility of N-substituted pyridinium salts in a non-aqueous solvent. We find a direct correlation between the number of C-H···π interactions for each pyridinium salt and its solubility in acetonitrile. The correlation presented in this work highlights a consequence of disrupting strong electrostatic interactions with weak dispersion interactions, showing how minimal structural change can dramatically impact pyridinium solubility.

Preparation, Crystal Structure, Supramolecular Assembly, and DFT Studies of Two Organic Salts Bearing Pyridine and Pyrimidine.

The effective preparation of two new pyrimidine- and pyridine-based organic crystalline salts with substituted acidic moieties (i.e., (Z)-4-(naphthalen-2-ylamino)-4-oxobut-2-enoic acid (DCNO) and 2-hydroxy-3,5-dinitrobenzoic acid (PCNP)) using methanol as a solvent has been reported. These molecular salts have ionic interactions that are responsible for their structural stabilization in their solid-state assemblies. The crystal structures of DCNO and PCNP were determined by the single-crystal X-ray diffraction (SCXRD) technique. The SCXRD study inferred that cations and anions are strongly packed due to N-H···O, N-H···N, and C-H···O noncovalent interactions in DCNO, whereas in PCNP, N-H···N noncovalent interactions are absent. The noncovalent interactions in both organic crystalline salts were comprehensively investigated by Hirshfeld surface analysis. Further, a detailed density functional theory (DFT) study of both compounds was performed. The optimized structures of both compounds supported the existence of the H-bonding and weak dispersion interactions in the synthesized organic crystalline salt structures. Both compounds were shown to have large and noticeably different HOMO/LUMO energy gaps. The atomic charge analysis results supported the SCXRD and HSA results, showing the formation of intermolecular noncovalent interactions in both organic crystalline salts. The results of the natural bond orbital (NBO) analysis confirmed the existence of (relatively weak) noncovalent interactions between the cation and anion moieties of their organic crystalline salts. The global reactivity parameters (GRPs) analysis showed that both organic crystalline salts' compounds should be quite thermodynamically stable and that DCNO should be less reactive than PCNP. For both compounds, the molecular electrostatic potential (MEP) analysis results support the existence of intermolecular electrostatic interactions in their organic crystalline salts.

Understanding and Describing London Dispersion Effects in ­Transition-Metal-Catalyzed C–H Activations

AbstractTransition-metal-catalyzed C–H activation has emerged as a powerful strategy for molecular synthesis with unique levels of resource economy. Weak secondary dispersion interactions were found to play an essential role in these transformations in terms of kinetic efficacy and selectivity. This Account summarizes our group’s recent progress in the rationalization and quantification of London dispersion effects within the transition-metal-catalyzed C–H activation.1 Introduction2 Annulation Reactions3 Alkylation Reactions4 Arylation Reactions5 Olefination Reactions6 Oxygenation Reactions7 Conclusion

Methylamine Magnesium Borohydrides as Electrolytes for All-Solid-State Magnesium Batteries

Solid-state magnesium electrolytes may pave the way for novel types of rechargeable, sustainable, and cheap batteries with high volumetric and gravimetric capacities. There are, however, currently no solid-state magnesium electrolytes that fulfill the requirements for solid-state battery applications. Here, we present the synthesis, structure, and properties of six new methylamine magnesium borohydride compounds, α- and β-Mg(BH4)2·6CH3NH2, Mg(BH4)2·3CH3NH2, and α-, α′- and β-Mg(BH4)2·CH3NH2. The β-Mg(BH4)2·CH3NH2 polymorph displays a record high Mg2+ ionic conductivity of σ(Mg2+) = 1.50 × 10–4 S cm–1 at room temperature. The high Mg2+ conductivity of β-Mg(BH4)·CH3NH2 is facilitated by a one-dimensional chain-like structure interconnected by weak dihydrogen bonds and dispersion interactions, forming a migration pathway across the chains. The oxidative stability of Mg(BH4)2·CH3NH2 is ∼1.2 V vs Mg/Mg2+, and the reversible plating and stripping were confirmed by cyclic voltammetry and symmetric cell cycling, revealing high stability toward magnesium electrodes for at least 50 cycles at 60 °C.

Synthesis, Structure and Mg2+ Ionic Conductivity of Isopropylamine Magnesium Borohydride

The discovery of new inorganic magnesium electrolytes may act as a foundation for the rational design of novel types of solid-state batteries. Here we investigated a new type of organic-inorganic metal hydride, isopropylamine magnesium borohydride, Mg(BH4)2∙(CH3)2CHNH2, with hydrophobic domains in the solid state, which appear to promote fast Mg2+ ionic conductivity. A new synthetic strategy was designed by combination of solvent-based methods and mechanochemistry. The orthorhombic structure of Mg(BH4)2∙(CH3)2CHNH2 was solved ab initio by the Rietveld refinement of synchrotron X-ray powder diffraction data and density functional theory (DFT) structural optimization in space group I212121 (unit cell, a = 9.8019(1) Å, b = 12.1799(2) Å and c = 17.3386(2) Å). The DFT calculations reveal that the three-dimensional structure may be stabilized by weak dispersive interactions between apolar moieties and that these may be disordered. Nanoparticles and heat treatment (at T > 56 °C) produce a highly conductive composite, σ(Mg2+) = 2.86 × 10−7, and 2.85 × 10−5 S cm−1 at −10 and 40 °C, respectively, with a low activation energy, Ea = 0.65 eV. Nanoparticles stabilize the partially eutectic molten state and prevent recrystallization even at low temperatures and provide a high mechanical stability of the composite.

Perturbative Diagonalization for Time-Dependent Strong Interactions

We present a systematic method to implement a perturbative Hamiltonian diagonalization based on the time-dependent Schrieffer-Wolff transformation. Applying our method to strong parametric interactions we show how, even in the dispersive regime, full Rabi model physics is essential to describe the dressed spectrum. Our results unveil several qualitatively different results, including realization of large energy-level shifts, tunable in magnitude and sign with the frequency and amplitude of the pump mediating the parametric interaction. Crucially, Bloch-Siegert shifts, typically thought to be important only in the ultrastrong or deep-strong coupling regimes, can be rendered large even for weak dispersive interactions to realize points of exact cancelation of dressed shifts (``blind spots'') at specific pump frequencies. The framework developed here highlights the rich physics accessible with time-dependent interactions and serves to significantly expand the functionalities for control and readout of strongly interacting quantum systems.

Structural landscape investigations on bendable plastic crystals of isonicotinamide polymorphs

Three polymorphs (forms I, II and V) of isonicotinamide (INA) were mechanically flexible and exhibited one-dimensional (1D) plasticity. Anisotropic intermolecular interactions contribute to the plasticity of single crystals: weak dispersive interactions between slip planes such as 1D columns in forms I and II or 2D layers in form V were stabilized by strong hydrogen bonds, allowing the layer or column's surface to glide smoothly without hindrance. The disparity of intermolecular interactions on plastic properties of INA polymorphic crystals was confirmed by energy framework analysis, nanoindentation tests and micro-Raman spectroscopy. The crystal which exhibits plastic property provides a promising application in pharmaceuticals and material sciences.

Cooperative Weak Dispersive Interactions Actuate Catalysis in a Shape-Selective Abiological Racemase.

A simple abiological host–guest system demonstrates racemase activity with catalytic rate enhancements of 104 without employing traditional functional groups. Cooperative weak interactions enhanced through shape-complementarity between the catalyst active site and the reaction transition state drive this activity, as proposed by Pauling for enzymes. In analogy to the Jencks’ concept of catalytic antibodies, it is shown that a hapten resembling the planar transition state of the bowl inversion acts as a potent inhibitor of this catalytic process. In contrast, no substrate/product inhibition is detected, and a relatively weak binding of the substrate is observed (Ka ≈ 102 M–1 at 293 K). This simple box-and-bowl system demonstrates that shape selectivity arising from cooperative dispersive forces suffices for the emergence of a catalytic system with an enzyme-like thermodynamic profile.

UV-selective organic absorbers for the cosensitization of greenhouse-integrated dye-sensitized solar cells: synthesis and computational study.

Molecular cosensitization is favorable for manipulating solar radiation through the judicious choice of cosensitizers having complementary absorption spectra. For greenhouse-integrated dye-sensitized solar cells (DSCs), the manipulation of solar radiation is crucial in order to maximize the flow of photosynthetically active radiation (PAR) for the effectual photosynthetic activity of plants; meanwhile, non-PAR is utilized in agrivoltaics for generating electricity. In this study, we report the synthesis of novel four UV-selective absorbers, based on the diimide scaffold, functionalized with carboxylate and pyridyl anchoring groups, for adequate adsorption onto the TiO2 electrode in DSC. The UV/Vis absorption spectra of the DMF solution-based free dyes were measured experimentally. Basic photophysical and energetics requirements for operating greenhouse-integrated DSCs were examined at the molecular level via (time-dependent) density functional theory-based calculations. The computational results revealed the outperformance of the biphenyldiimide-structured DI-CA1 dye, especially for maximum charge transferred to its anchor, lower thermodynamic barrier for dissociating the photogenerated exciton, largest Stokes' shift, strong electronic coupling with TiO2 nanoparticles, and higher degree of charge separation at the DI-CA1/TiO2 interface. PDOS showed deeper existence for the LUMO level in the CB of TiO2, which expedites the electron injection process. The chemical and optical compatibility of DI-CA1 were then investigated as a potential cosensitizer of a reference BTD–DTP1, a green light-absorbing dye. Considerable overlap between the fluorescence spectrum of DI-CA1 and absorption spectrum of the reference BTD–DTP1 advocated the opportunity of excitation energy transfer via the radiative trivial reabsorption mechanism, which confirms the cosensitization functionality. Energy decomposition analysis and reduced density gradient maps estimated the chemical compatibility owing to weak dispersion interactions as the dominant stabilizing attractive force. This noncovalent functionalization retains the chemical compatibility without distorting the π–π conjugation and the associated physicochemical properties of the individual dye molecules. Along with the expanded consumption of non-photosynthetically active solar radiation, an improved power conversion efficiency of greenhouse-integrated DSC is accordingly expected.

Flexible organic crystals. Understanding the tractable co-existence of elastic and plastic bending.

As an emerging class of flexible materials, mechanically bendable molecular crystals are broadly classified as elastic or plastic. Nevertheless, flexible organic crystals with mutually exclusive elastic and plastic traits, with contrasting structural requirements, co-existing under different stress settings are exceptional; hence, it is imperative to establish the concurring factors that beget this rare occurrence. We report a series of halogen-substituted benzil crystals showing elastic bending (within ∼2.45% strain), followed by elastoplastic deformation under ambient conditions. Under higher stress settings, they display exceptional plastic flexibility that one could bend, twist, or even coil around a capillary tube. X-ray diffraction, microscopy, and computational data reveal the microscopic and macroscopic basis for the exciting co-existence of elastic, elastoplastic, and plastic properties in the crystals. The layered molecular arrangement and the weak dispersive interactions sustaining the interlayer region provide considerable tolerance towards breaking and making upon engaging or releasing the external stress; it enables restoring the original state within the elastic strain. Comparative studies with oxalate compounds, wherein the twisted diketo moiety in benzil was replaced with a rigid and coplanar central oxalate moiety, enabled us to understand the effect of the anisotropy factor on the crystal packing induced by the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O⋯C tetral interactions. The enhanced anisotropy depreciated the elastic domain, making the oxalate crystals more prone to plastic deformation. Three-point bending experiments and the determined Young's moduli further corroborate the co-existence of the elastic and plastic realm and highlight the critical role of the underlying structural elements that determine the elastic to plastic transformation. The work highlights the possible co-existence of orthogonal mechanical characteristics in molecular crystals and further construed the concurrent role of microscopic and macroscopic elements in attaining this exceptional mechanical trait.

π‐Extended Bodipy Self‐Assembly as Supramolecular Photonic Security Ink and Optical Waveguide

AbstractIridescent photonic materials have wide‐ranging applications in security printing, and optical devices. While the commonly used photonic materials are based on polymers or inorganic colloidal particles, self‐assembled small molecules are rarely exploited. Herein, a Bodipy (Bodipy‐PE‐2) self‐assembly is reported that forms a layered photonic structure upon thermal annealing, exhibiting angle‐dependent iridescence of green and pink with a luminescence shift from yellow to red. The micro‐ and nano‐periodicity associated with the layered structure and the phase transformation due to the annealing are responsible for the observed properties. The single‐crystal analysis reveals the critical role of weak dispersive interactions (C–H···π, C–H···O, and N–H···F) in the crystal packing and a possible phase change in the formation of the layered structure. A stimuli‐responsive ink prepared with the annealed powder using polyethylene glycol as a vehicle medium exhibits reversible emission change between red and yellow upon heating and solvent exposure, respectively. A composite gel of the annealed Bodipy‐PE‐2 and polystyrene displays angle‐dependent color change and optical waveguiding properties. The self‐assembled Bodipy‐PE‐2 obtained from toluene exhibits active and passive waveguiding properties when excited with 532 and 633 nm laser sources.

Solvophobicity-directed assembly of microporous molecular crystals

Dense packing is a universal tendency of organic molecules in the solid state. Typical porous crystals utilize reticular strong intermolecular bonding networks to overcome this principle. Here, we report a solvophobicity-based methodology for assembling discrete molecules into a porous form and succeed in synthesizing isostructural porous polymorphs of an amphiphilic aromatic molecule Py6Mes. A computational analysis of the crystal structure reveals the major contribution of dispersion interaction as the driving force for assembling Py6Mes into a columnar stacking while the columns are sterically salient and form nanopores between them. The porous packing is facilitated particularly in solvents with weak dispersion interaction due to the solvophobic effect. Conversely, solvents with strong dispersion interaction intercalate between Py6Mes due to the solvophilic effect and provide non-porous inclusion crystals. The solvophobicity-directed polymorphism is further corroborated by the polymorphs of Py6Mes-analogues, m-Py6Mes and Ph6Mes.

Interaction between organic molecules and a gold nanoparticle: a quantum chemical topological analysis

The ligands at the surface of a gold nanoparticle (GNP) have a significant influence on the optical and physical properties, that may render different functionalities to the GNP. Therefore, there is a need in understanding the nature of the interaction at atomic resolution in order to allow rational design of GNPs with desired physico-chemical properties. The interaction between Au $$_{79}$$ and a series of small organic molecules has been systematically studied at the quantum mechanical level : methane, methanol, formic acid, hydrogen sulfide, benzene, and ammonia. The reactivity of Au $$_{79}$$ has been first analyzed by performing the condensed Fukui analysis to emphasize that the surface of Au $$_{79}$$ is dominated by electrophilic sites, with higher reactivity at the corner and edge atoms. The net charge transfer flowing from the organic molecules toward Au $$_{79}$$ comes from the electrophilic behavior of the GNP. Furthermore, the shape of the frontier molecular orbitals of Au $$_{79}$$ and of the incoming organic molecules has been found to dictate the preferred orientation of the adsorption. Several quantum chemical topological analyses of the electron density have been performed to further classify the interactions to weak dispersive or van der Waals interactions in methane and stronger non-covalent interactions in ammonia, benzene, hydrogen sulfide, methanol, and formic acid. The analysis of the electron localization function (ELF), on the other hand, provides more insight about the charge transfer, as the population of the basins of the organic molecules has decreased after interacting with Au $$_{79}$$ .

Self-assembly of curved aromatic molecules in nanoparticles

The self-assembly and structure of nanoparticles containing curved polycyclic aromatic hydrocarbon molecules (cPAHs) are investigated using molecular modelling. These polar fullerene-like molecules are receiving increased attention recently due to the steric and electronic properties caused by the inclusion of five-membered ring(s) within their hexagonal lattice. In this work, the curPAHIP potential is extended to describe the interactions between large cPAHs. It is then used within molecular dynamics simulations to produce nanoparticles containing cPAHs. Structural and energetic metrics, including diameter, density, intermolecular spacing, coordination number, alignment angle, radial distance, and energy value, are used to analyse systems containing cPAHs of different sizes and ratios, and containing flat PAHs or ions. Homogeneous cPAH particles are more tightly packed than their flat PAH counterparts, with large cPAHs displaying stacked columnar configurations absent in nanoparticles containing small cPAHs. Mixing cPAHs of different sizes disrupts the ordered mesophase and forms a core-shell structure in which the larger molecules make up the core and the smaller molecules comprise the shell, although this partitioning is less distinct compared to flat PAHs. In addition, the presence of flat PAHs and ions within cPAH nanoparticles promotes distinct arrangements dominated by weak dispersive interactions and strong electrostatic interactions, respectively.

Vacuum Ultraviolet Photoionization Induced Proton Migration and Formation of a New C-N Bond in Pyridine Clusters Revealed by Infrared Spectroscopy and Mass Spectrometry.

The structures and reactions of pyridine (Pyd) cluster cations in a supersonic molecular beam generated upon photoionization at 9.2-9.4 eV were investigated by infrared (IR) action spectroscopy. The mass spectrum showed prominent peaks of (Pyd)m+ and H+(Pyd)m, m = 1-5. In the pyridine/pyridine-d5 mixture, the mass pattern indicated that H+ and D+ migrated during the formation and dissociation of the cluster cations. The IR photodissociation spectra of both (Pyd)2+ and H+(Pyd)2 revealed a N-H stretching band near 3400 cm-1, indicating that their structures are 1-(2-pyridyl)pyridin-1-ium and pyridinium-pyridine, respectively. Observation of the former product implies that the reaction proceeds via an α-distonic cation intermediate, while the latter product is formed via proton migration. The IR spectra of (Pyd)m+ and H+(Pyd)m, m ≥ 3, suggested that these clusters consist of a covalently bound (Pyd)2+ or H+(Pyd)2 core, respectively, with additional pyridines attached to them via hydrogen bonds and/or weak dispersive interactions.

Enantioselective Ruthenium-Catalyzed C-H Alkylations by a Chiral Carboxylic Acid with Attractive Dispersive Interactions.

Asymmetric ruthenium-catalyzed C-H alkylations were enabled by a chiral C2-symmetric carboxylic acid. The mild cooperative ruthenium(II) catalysis set the stage for the assembly of chiral tetrahydrocarbazoles and cyclohepta[b]indoles with high levels of enantioselectivity at room temperature. Mechanistic studies by experiment and computation identified a fast C-H ruthenation, along with a rate- and enantio-determining proto-demetalation. The asymmetric induction was governed by weak attractive secondary dispersion interactions as found in NCI analysis of the key transition states.