Attractive Dispersion Interactions Research Articles

A lithium-aluminium heterobimetallic dimetallocene.

Homobimetallic dimetallocenes exhibiting two identical metal atoms sandwiched between two η5 bonded cyclopentadienyl rings is a narrow class of compounds, with representative examples being dizincocene and diberyllocene. Here we report the synthesis and structural characterization of a heterobimetallic dimetallocene, accessible through heterocoupling of lithium and aluminylene fragments with pentaisopropylcyclopentadienyl ligands. The Al-Li bond features a high ionic character and profits from attractive dispersion interactions between the isopropyl groups of the cyclopentadienyl ligands. A key synthetic step is the isolation of a cyclopentadienylaluminylene monomer, which also enables the structural characterization of this species. In addition to their structural authentication by single-crystal X-ray diffraction analysis, both compounds were characterized by multinuclear NMR spectroscopy in solution and in the solid state. Furthermore, reactivity studies of the lithium-aluminium heterobimetallic dimetallocene with an N-heterocyclic carbene and different heteroallenes were performed and show that the Al-Li bond is easily cleaved.

Influence of Steric and Dispersion Interactions on the Thermochemistry of Crowded (Fluoro)alkyl Compounds.

ConspectusAlkanes play a pivotal role in industrial, environmental, and biological processes. They are characterized by their carbon-carbon single-bond structure, remarkable stability, and conformational diversity. Fluorination of such compounds imparts unique physicochemical properties that often enhance pharmacokinetic profiles, metabolic stability, and receptor interactions while keeping beneficial properties. However, such per- and polyfluoroalkyl substances (PFAS) show a persistent presence in the environment and potential adverse health effects, which propelled them to the forefront of global environmental and health discussions. Alkyl compounds are also prototypical for stereoelectronic (SE) effects that are widely applied in chemistry. Substituents are typically described as electron-density-donating/withdrawing and/or responsible for sterically interacting with reagents or strategic groups in the molecule. That alkane branching can result in higher stability compared to less-branched isomers has been investigated in detail also by testing quantum chemical methods, in particular density functional theory (DFT). Alkane branching results in spatially compact structures with close intramolecular contacts so that at a specific size the detailed balance of attractive London dispersion and covalent versus repulsive Pauli exchange interactions shifts to new, chemically unfragile situations. This may lead to dissociation at room temperature and opens the central question: what is the smallest crowed alkane that cannot be made synthetically? In this Account, we try to shed light on the interplay among the various (free) energy components for crowded (fluoro)alkane dissociation. In this context, homolytic cleavage of the central C-C bond in a series of model alkanes of increasing size with tert-butyl (tBu), adamantyl (Ad), and [1.1.1]propellanyl (Prop) substituents is investigated. Reference energies are calculated at the PNO-LCCSD(T)-F12b level and used to benchmark the performance of contemporary DFT functionals. In line with previous conclusions, the application of dispersion corrections to density functionals is mandatory. For crowed structures, the accurate description of the midrange correlation effects, specifically repulsive van der Waals interactions, is crucial, and we observed that the density-dependent VV10 correction is superior to D4 in this context, although the asymptotic region is better described by the latter. The best available dispersion-inclusive functionals show systematic and reasonably small residual errors and can be safely applied to large systems (>100 atoms), for which coupled cluster methods with large basis sets are not computationally feasible anymore. For qualitatively correct predictions of synthetic accessibility under equilibrium conditions (free energy), the inclusion of thermostatistical (entropy) contributions is also essential. According to our results, tetra-tert-butylmethane (C17tBu) is the largest and most crowded system with a positive dissociation free energy and should be synthesizable. The difference between hydrogenated and perfluorinated systems originates from the increase in the steric repulsion of spatially close substituents, which is not compensated to the same extent by attractive orbital and dispersion interactions. A sometimes-assumed similar steric demand for fluorine and hydrogen atoms is not corroborated by our investigations on crowded systems. Perfluorination is found to substantially decrease thermal stability, rendering perfluorinated hexamethylethane (C8tBuF) the last potentially stable representative.

Contributions of London Dispersion Forces to Solution-Phase Association Processes.

ConspectusDespite their ubiquity and early discovery, London dispersion forces are often overlooked. This is due, in part, to the difficulty in assessing their contributions to molecular and polymeric structure, stability, properties, and reactivities. However, recent advances in modeling have revealed that dispersion interactions play an important role in many important chemical and biological processes. Experimental confirmation of their impact in solution has been challenging, leading to controversies about their relative importance.In the course of studying noncovalent interactions using molecular devices, our understanding and appreciation for the importance of dispersion interactions have evolved. This Account follows this intellectual journey by using examples from the literature. The goals are twofold: to describe recent advances in understanding the interaction and to provide guidance to researchers studying weak noncovalent interactions. However, first, the experimental methods for measuring the effects of dispersion interactions and the strategies for isolating their influence are described. These include the design of molecular devices to measure these weak noncovalent interactions and the strategies to disentangle the solvation, solvophobic, and dispersion components of the resulting equilibria.The literature examples are organized around five fundamental questions. (1) Do dispersion interactions have a measurable effect on solution equilibria? (2) To what extent do solvents attenuate or compensate for dispersion interactions? (3) To what extent do the solvation and solvophobic terms influence the dispersion equilibria? (4) Can we predict whether a system will form attractive dispersion or repulsive steric interactions? (5) Can the dispersion term be isolated and interrogated? We were often surprised by the answers to these questions. In each case, we describe how the systems were designed to address these questions and discuss possible interpretations of the results.While dispersion interactions in solution were weak (usually <1 kcal/mol), their influence on complexation and conformational equilibria can be observed and measured. This underscores the significance of these interactions in molecular recognition, coordination chemistry, reaction design, and catalysis. The solvent components of the dispersion equilibria can also be significant. Therefore, the isolation of the dispersion contributions from the solvation and solvophobic effects represents an ongoing challenge. The experimental studies also provide important benchmarks and offer valuable insights to help refine the next generation of computational solvent models.

State-to-state rovibrational transition rates for CO2 in the bend mode in collisions with He atoms.

Modeling environments that are not in local thermal equilibrium, such as protoplanetary disks or planetary atmospheres, with molecular spectroscopic data from space telescopes requires knowledge of the rate coefficients of rovibrationally inelastic molecular collisions. Here, we present such rate coefficients in a temperature range from 10 to 500K for collisions of CO2 with He atoms in which CO2 is (de)excited in the bend mode. They are obtained from numerically exact coupled-channel (CC) calculations as well as from calculations with the less demanding coupled-states approximation (CSA) and the vibrational close-coupling rotational infinite-order sudden (VCC-IOS) method. All of the calculations are based on a newly calculated accurate abinitio four-dimensional CO2-He potential surface including the CO2 bend (ν2) mode. We find that the rovibrationally inelastic collision cross sections and rate coefficients from the CSA and VCC-IOS calculations agree to within 50% with the CC results at the rotational state-to-state level, except for the smaller ones and in the low energy resonance region, and to within 20% for the overall vibrational quenching rates except for temperatures below 50K where resonances provide a substantial contribution. Our CC quenching rates agree with the most recent experimental data within the error bars. We also compared our results with data from Clary et al. calculated in the 1980s with the CSA [A. J. Banks and D. C. Clary, J. Chem. Phys. 86, 802 (1987)] and VCC-IOS [D. C. Clary, J. Chem. Phys. 78, 4915 (1983)] methods and a simple atom-atom model potential based on abinitio Hartree-Fock calculations and found that their cross sections agree fairly well with ours for collision energies above 500 cm-1, but that the inclusion of long range attractive dispersion interactions is crucial to obtain reliable cross sections at lower energies and rate coefficients at lower temperatures.

Copper-Catalyzed Chemoselective Asymmetric Hydrogenation of C=O Bonds of Exocyclic α,β-Unsaturated Pentanones.

A highly chemoselective earth-abundant transition metal copper catalyzed asymmetric hydrogenation of C=O bonds of exocyclic α, β-unsaturated pentanones was realized using H2. The desired products were obtained with up to 99% yield and 96% ee (enantiomeric excess) (99% ee, after recrystallization). The corresponding chiral exocyclic allylic pentanol products can be converted into several bioactive molecules. The hydrogenation mechanism was investigated via deuterium-labelling experiments and control experiments, which indicate that the keto-enol isomerization rate of the substrate is faster than that of the hydrogenation and also show that the Cu-H complex can only catalyze chemoselectively the asymmetric reduction of the carbonyl group. Computational results indicate that the multiple attractive dispersion interactions (MADI effect) between the catalyst with bulky substituents and substrate play important roles which stabilize the transition states and reduce the generation of by-products.

Copper‐Catalyzed Chemoselective Asymmetric Hydrogenation of C=O Bonds of Exocyclic α,β‐Unsaturated Pentanones

AbstractA highly chemoselective earth‐abundant transition metal copper catalyzed asymmetric hydrogenation of C=O bonds of exocyclic α,β‐unsaturated pentanones was realized using H2. The desired products were obtained with up to 99 % yield and 96 % ee (enantiomeric excess) (99 % ee, after recrystallization). The corresponding chiral exocyclic allylic pentanol products can be converted into several bioactive molecules. The hydrogenation mechanism was investigated via deuterium‐labelling experiments and control experiments, which indicate that the keto‐enol isomerization rate of the substrate is faster than that of the hydrogenation and also show that the Cu−H complex can only catalyze chemoselectively the asymmetric reduction of the carbonyl group. Computational results indicate that the multiple attractive dispersion interactions (MADI effect) between the catalyst with bulky substituents and substrate play important roles which stabilize the transition states and reduce the generation of by‐products.

Origin of structure and stability of M@C18 (M = Cu, Ag, and Au) complexes with D9h point group.

Theoretical predictions and recent experimental studies lead to the discovery of an exciting new member of the carbon allotrope family polyynic cyclo[18]carbon (C18 ). Present investigation aims to probe the structure, stability, and properties of coinage metal (M)@C18 complexes using density functional theory (DFT) calculations. The DFT results unequivocally show that even Cu@C18 , Ag@C18 , and Au@C18 complexes substantially preserve the ground state polyynic structure of C18 . It is also worth to mention that only Au@C18 is a stable D9h structure, however the symmetry is distorted in the case of Cu@C18 and Ag@C18 . Due to computational limitations, in this investigation the M@C18 complexes were scrutinized using the C2v sub abelian group of D9h . The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of D9h conformers are a singlet a1 and two same value singlets a1 ⊕ b1 generated from doublet e, respectively. The non-covalent interaction index (NCI), quantum theory of atoms in molecule (QTAIM), and energy decomposition analysis (EDA) vividly explains the interaction between a coinage metal atom and C18 ring. It is found from the results that the stability of Cu@C18 Ag@C18 , and Au@C18 is governed by the attractive electrostatic, orbital and dispersion interaction.

The role of attractive dispersion interaction in promoting the catalytic activity of asymmetric hydrogenation

This study proves Wanbin Zhang's finding that weak attractive interactions between substrate and ligand play an important role in metal-catalyzed asymmetric hydrogenations and shows that the dispersion interaction is the major attractive interaction.

Non-Covalent Interactions in Triglycerides: Vaporisation Thermodynamics for Quantification of Dispersion Forces

Qualitatively, the non-covalent interactions are well-known and help to explain many phenomena in chemistry and biochemistry. Quantitatively, determination of strength this force is a challenging task. The vaporization enthalpy is a reliable measure not only for the intermolecular interactions in the liquid phase, but also as the measure of intermolecular non-covalent interactions in the gas phase for the specific group of compounds, e.g., for the triglycerides. The vaporisation thermodynamics of four triglycerides were studied by using transpiration method, quartz crystal microbalance, and thermogravimetric analysis. Vapour pressure–temperature dependences were used to derive the enthalpies of vaporisation of these very low volatile liquids. Vaporisation enthalpies of the triglycerides available in the literature were collected and uniformly adjusted to the reference temperature 298.15 K and validated using structure–property relationships (chain-length dependence, correlation with retention indices, and correlation with normal boiling points). The consistent sets of evaluated vaporisation enthalpies for the linear and branched triglycerides were used to develop the “centerpiece” based group-additivity method for predicting enthalpies of vaporisation of triglycerides. It has turned out that the family of triglycerides do not obey the group-additivity rules. The reason for that is that the evaporated in the gas phase triglycerides exhibit intensive non-covalent attractive dispersion interactions strongly dependent on the alkyl-chain length. For the first time the intensity of the dispersion interactions was quantified for the family of aliphatic linear triglycerides with the chain length from 3 to 18 carbon atoms. The influence of the branching and unsaturation of the alkyl chains to the strength of the non-covalent interactions was also discussed.

Dispersion Interactions between Molecules in and out of Equilibrium Geometry: Visualization and Analysis.

The London dispersion interactions between systems undergoing bond breaking, twisting, or compression are not well studied due to the scarcity and the high computational cost of methods being able to describe both the dynamic correlation and the multireference character of the system. Recently developed methods based on the Generalized Valence Bond wave function, such as EERPA-GVB and SAPT(GVB) (SAPT = symmetry-adapted perturbation theory), allow one to accurately compute and analyze noncovalent interactions between multireference systems. Here, we augment this analysis by introducing a local indicator for dispersion interactions inspired by Mata and Wuttke’s Dispersion Interaction Density [J. Comput. Chem.2017, 38, 15−2327761924] applied on top of an EERPA-GVB computation. Using a few model systems, we show what insights into the nature and evolution of the dispersion interaction during bond breaking and twisting such an approach is able to offer. The new indicator can be used at a minimal cost additional to an EERPA-GVB computation and can be complemented by an energy decomposition employing the SAPT(GVB) method. We explain the physics behind the initial increase, followed by a decrease in the interaction of linear molecules upon bond stretching. Namely, the elongation of covalent bonds leads to the enhancement of attractive dispersion interactions. For even larger bond lengths, this effect is canceled by the increase of the repulsive exchange forces resulting in a suppression of the interaction and finally leading to repulsion between monomers.

Dispersion and Steric Effects on Enantio-/Diastereoselectivities in Synergistic Dual Transition-Metal Catalysis.

Comprehensive computational studies were carried out to explore the mechanisms of enantioselective Cu/Pd and stereodivergent Cu/Ir dual-catalytic syntheses of α,α-disubstituted α-amino acids (α-AAs). A chiral copper azomethine ylide undergoes facile α-allylation with racemic π-allylpalladium species or stereopure π-allyliridium complex to stereoconvergently or stereodivergently furnish single/double stereocenters, respectively. Stereoselectivity at the α-center is controlled by the facial selectivity of α-allylation with respect to the prochiral nucleophile. Despite apparently similar transition-state assemblies, computational models and distortion/interaction analyses disclose versatile modes of stereoinduction wherein the copper azomethine ylide species can face-selectively intercept metal-π-allyl intermediates utilizing attractive dispersion interactions and/or sterically caused distortions. Generation of the β-stereocenter in the Cu/Ir system relies on a stereospecifically generated allyliridium complex and electronically controlled branched-to-linear selectivity, while the dual Cu/Pd system yields a linear monochiral product due to steric factors and π-π stacking interactions. The studies demonstrate on a molecular level how ligand-encoded chiral information is transferred to the α-/β-sites of the resulting α-AAs and how the mode of regio-/stereoselection is altered by differences in transition-metal-stabilized coupling partners. To facilitate studies of stereoselective catalysis, a suite of analytical tools to extract controlling factors for asymmetric induction is demonstrated.

Surface morphology and dispersion interaction induced anomalous dynamics of solvation water of a hydrophobic fullerene molecule

Knowledge of accurate structural and dynamical features of the surrounding water of a C60 molecule is essential for the proposed uses of C60 in a wide variety of applications viz., in inhibiting HIV protease, DNA cleaving, macromolecular binding and drug delivery. Using molecular dynamics simulations, the present study demonstrates that the solute-water dispersion interaction induces anomalous bulk density dependence of dynamics of solvation water of the C60. In order to elucidate the origin of such behaviour, the analyses of the simulation trajectories are performed and it reveals the presence of two dynamically different types of water molecules: one (designated as Type 1 here), which has no radially outward movements (with respect to C60) throughout the simulation time and performs “bouncing ball” movements on the C60 surface by hopping from one face to another and the other one (Type 2) is fast and goes in and out of the solvation shell frequently. The anomalous dynamics is a consequence of the variable presence of such dynamically heterogeneous water molecules as a function of bulk density, and it, in turn, arises due to the interplay between two opposing effects emanating from the free volume (which depends on bulk density) and the inhomogeneous energy surface of the C60 arising due to icosahedral arrangement of carbon atoms on the surface and attractive solute-water dispersion interaction. It is to emphasize that model C60 with no attractive dispersion interaction does not show any anomalous dynamics.

Cobalt-Catalyzed Enantioselective C-H Arylation of Indoles.

Atropoisomeric (hetero)biaryls are scaffolds with increasing importance in the pharmaceutical and agrochemical industries. Although it is the most obvious disconnection to construct such compounds, the direct enantioselective C-H arylation through the concomitant induction of the chiral information remains extremely challenging and uncommon. Herein, the unprecedented earth-abundant 3d-metal-catalyzed atroposelective direct arylation is reported, furnishing rare atropoisomeric C2-arylated indoles. Kinetic studies and DFT computation revealed an uncommon mechanism for this asymmetric transformation, with the oxidative addition being the rate- and enantio-determining step. Excellent stereoselectivities were reached (up to 96% ee), while using an unusual N-heterocyclic carbene ligand bearing an essential remote substituent. Attractive dispersion interactions along with positive C-H---π interactions exerted by the ligand were identified as key factors to guarantee the excellent enantioselection.

Quantum-mechanical force balance between multipolar dispersion and Pauli repulsion in atomic van der Waals dimers

The structure and stability of atomic and molecular systems with van der Waals (vdW) bonding are often determined by the interplay between attractive dispersion interactions and repulsive interactions caused by electron confinement. Arising due to different mechanisms -- electron correlation for dispersion and the Pauli exclusion principle for exchange-repulsion -- these interactions do not appear to have a straightforward connection. In this paper, we use a coarse-grained approach for evaluating the exchange energy for two coupled quantum Drude oscillators and investigate the mutual compensation of the attractive and repulsive forces at the equilibrium distance within the multipole expansion of the Coulomb potential. This compensation yields a compact formula relating the vdW radius of an atom to its multipole polarizabilities, $R_{\rm vdW} = A_l^{\,}\, \alpha_l^{{2}/{7(l+1)}}$, where $l$ is the multipole rank and $A_l$ is a conversion factor. Such a relation is compelling because it connects an electronic property of an isolated atom (atomic polarizability) with an equilibrium distance in a dimer composed of two closed-shell atoms. We assess the accuracy of the revealed formula for noble-gas, alkaline-earth, and alkali atoms and show that the $A_l$ can be assumed to be universal constants. Besides a seamless definition of vdW radii, the proposed relation can also be used for the efficient determination of atomic multipole polarizabilities solely based on the corresponding dipole polarizability and the vdW radius. Finally, our work provides a basis for the construction of efficient and minimally-empirical interatomic potentials by combining multipolar interatomic exchange and dispersion forces on an equal footing.

Could London Dispersion Force Control Regioselective (2 + 2) Cyclodimerizations of Benzynes? YES: Application to the Synthesis of Helical Biphenylenes.

In recent years, London dispersion interactions, which are the attractive component of the van der Waals potential, have been found to play an important role in controlling the regio- and/or stereoselectivity of various reactions. Particularly, the dispersion interactions between substrates and catalysts (or ligands) are dominant in various selective catalyzes. In contrast, repulsive steric interactions, rather than the attractive dispersion interactions, between bulky substituents are predominant in most of the noncatalytic reactions. Herein, we demonstrate the first example of London dispersion-controlled noncatalytic (2 + 2) cyclodimerization of substituted benzynes to selectively afford proximal biphenylenes in high yields and regioselectivities, depending on the extent of dispersion interactions in the substituents. This method can be applied for the synthesis of novel helical biphenylenes, which would be fascinating for chemists as these compounds are potential skeletons for ligands, catalysts, and medicines.

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.

Application of Trimethylgermanyl-Substituted Bisphosphine Ligands with Enhanced Dispersion Interactions to Copper-Catalyzed Hydroboration of Disubstituted Alkenes.

We report the incorporation of large substituents based on heavy main-group elements that are atypical in ligand architectures to enhance dispersion interactions and, thereby, enhance enantioselectivity. Specifically, we prepared the chiral biaryl bisphosphine ligand (TMG-SYNPHOS) containing 3,5-bis(trimethylgermanyl)phenyl groups on phosphorus and applied this ligand to the challenging problem of enantioselective hydrofunctionalization reactions of 1,1-disubtituted alkenes. Indeed, TMG-SYNPHOS forms a copper complex that catalyzes hydroboration of 1,1-disubtituted alkenes with high levels of enantioselectivity, even when the two substituents are both primary alkyl groups. In addition, copper catalysts bearing ligands possessing germanyl groups were much more active for hydroboration than one derived from DTBM-SEGPHOS, a ligand containing 3,5-di-tert-butyl groups and widely used for copper-catalyzed hydrofunctionalization. This observation led to the identification of DTMGM-SEGPHOS, a bisphosphine ligand bearing 3,5-bis(trimethylgermanyl)-4-methoxyphenyl groups as the substituents on the phosphorus, as a new ligand that forms a highly active catalyst for hydroboration of unactivated 1,2-disubstituted alkenes, a class of substrates that has not readily undergone copper-catalyzed hydroboration previously. Computational studies revealed that the enantioselectivity and catalytic efficiency of the germanyl-substituted ligands is higher than that of the silyl and tert-butyl-substituted analogues because of attractive dispersion interactions between the bulky trimethylgermanyl groups on the ancillary ligand and the alkene substrate and that Pauli repulsive interactions tended to decrease enantioselectivity.

Molecular Dynamics Simulations of Aqueous Nonionic Surfactants on a Carbonate Surface

The interactions and structure of secondary alcohol ethoxylates with 15 and 40 ethoxylate units in water near a calcite surface are studied. It is found that water binds preferentially to the calcite surface. Prediction of the free-energy landscape for surfactant molecules shows that single-surfactant molecules do not adsorb because they cannot get close enough to the surface because of the water layer for attractive ethoxylate-calcite or dispersion interactions to be significant. Micelles can adsorb onto the surface even with the intervening water layer because of the integrative effect of the attractive interactions of all the surfactant molecules. Adsorption is found to increase because of the closer proximity of the micelles to the surface due to a weakened water layer at higher temperatures. The free-energy well and barrier values are used to estimate surface to bulk partition coefficients for different surfactants and temperatures, and qualitative agreement is found with experimental observations. The combined effect of surfactant-water and surfactant-solid interactions is found to be responsible for an increased adsorption for nonionic surfactants as the system approaches the cloud point.

From 2D to 3D solids: stacking of transition metal nitroprusside layers through intermolecular physical interactions

This contribution reports the preparation and study of a series of hybrid inorganic-organic solids obtained by intercalation of pyridine molecules between neighboring layers of 2D transition metal nitroprussides, T[Fe(CN)5NO]. The pyridine molecule coordinated to the axial positions for the metal (T) linked at the N ends of the equatorial CN ligands. From such regular pyridine molecule disposition at the layer and the attractive dispersive interactions and dipole-dipole coupling between neighboring molecules in the interlayer region, the formation of a long range 3D framework results. The refined crystal structure and the magnetic measurements shed light on the interaction between intercalated neighboring molecules. In the resulting 3D framework, the hybrid material preserves its 2D identity because no formation of chemical bonds is involved in the stacking process. Such structural features are properly supported by the refined crystal structures and computational studies for the interaction of the organic molecule with the metal (T) center. This series of hybrid solids crystallizes with an orthorhombic unit cell in the Ic2m space group. The unit cell volume shows a slight dependence of the metal (T), Ni < Co < Zn < Mn, which is related to the metal polarizing power and follows the order found for the T-NCN and T-NPy bond distances. The results herein discussed are relevant for hybrid inorganic-organic materials design, preparation and applications.

Molecular designs for expanding the limits of ultralong C-C bonds and ultrashort HH non-bonded contacts.

Recent experiments have reported the formation of very long C-C bonds (dC-C > 1.80 Å) and very short HH non-bonded contacts (dHH < 1.5 Å) in several sets of molecules. Both these rare phenomena arise due to specific donor-acceptor interactions and London dispersion interactions respectively. Favorable negative hyperconjugation, namely H2N(lone-pair) →σ*(C-C), creates an ultralong C-C bond in diamino-o-carborane with dC-C > 1.829 Å and a planar amine reminiscent of a transition-state like structure for ammonia inversion. The small and narrow barrier favours rapid inversion through quantum mechanical tunnelling (QMT) and produces a translationally averaged planar amine as observed in the experiments. On the other hand, designing specific confined molecular cavities or chambers like in,in-bis(hydrosilane) or its germanane analogs furnishes an ultrashort HH distance = 1.47 Å and 1.38 Å respectively. The predisposition of such closely placed HH contacts arises from the rather effective attractive dispersion interactions between them. Controlling the strength of the dispersion interactions provides a rich landscape for realizing such close HH distances. Molecular design ably assisted by computational modeling to further tune these interactions provides new avenues to break the glass-ceilings of ultralong C-C bonds or ultrashort HH contacts. Dispersion-corrected DFT calculations and ab initio molecular dynamics simulations generate a large library of such unique features in a diverse class of molecules. This feature article highlights the design principles to realize hitherto longest C-C bonds/shortest HH contacts.