What is NBO analysis and how is it useful?

Abstract

Natural bond orbital (NBO) analysis is one of many available options for 'translating' computational solutions of Schrödinger's wave equation into the familiar language of chemical bonding concepts. In this Review, we first address the title questions by describing characteristic features that distinguish NBO from alternative analysis methodologies (e.g. of QTAIM or EDA type) and answering criticisms that have been raised in specific chemical applications. We then address the general 'usefulness' of NBO analysis in the context of widely accepted philosophical criteria, including (i) broad consistency, both internally and with respect to known experimental data, (ii) multi-faceted predictive capacity, including numerical model predictions of specific properties, general correlative and statistical regression relationships, and 'risky' falsifiable predictions of previously unknown chemical phenomena, and (iii) general pedagogical value, promoting organisation, unification, and orderly rationalisation of chemical knowledge. Specific chemical topics chosen for discussion include controversial H⋯H 'bond lines' in bay-type hydrocarbon species; carbene ligation of coinage metals; resonance-type bonding of noble gas hydrides; NBO descriptors in Hammett-type quantitative structure-activity relationships; nature of conventional and 'anti-electrostatic' hydrogen bonding interactions; multi-centre bonding in 'aromatic' Al ð2ÀÞ 4 , Lewis-like hybridisation picture of non-VSEPR geometry and high-order multiple bonding in transition metal species; resonance origin of the '18e rule'; and localised (symmetry-independent) prediction of Jahn-Teller effects in free radical chemistry. We conclude with hints of some directions for future extensions of NBO methods.

When Like Charged Ions Attract in Ionic Liquids: Controlling the Formation of Cationic Clusters by the Interaction Strength of the Counterions

“…As shown in Figure 6 the relation is nearly linear. [30][31][32] Despite strong electrostatic opposition, cation-cation clusters are found to be in equilibrium with cation-anion species upon reaching typical H-bond distances and spectroscopic signatures as known for molecular liquids (see Supporting Information). In contrast, the weaker cation-anion interaction as present in I results in moderate downfield chemical shifts (d = 3.4 ppm) and highest frequencies (ñ = 3550 cm À1 ).…”

Evaluation of the Alicyclic Gauche Effect in 2‐Fluorocyclohexanone Analogs: a Combined NMR and DFT Study

“…To estimate the contribution of the hyperconjugative interactions featured in the gauche effect to the conformational energies, we looked at the second order perturbation energy [ E i → j (2) = 2 F ( i,j ) 2 /( ε j – ε i ), F ( i,j ) is the off‐diagonal matrix element, ε j and ε i are the orbital energies] in the NBO analysis that estimates delocalization energies from orbital interactions (Table S5 of the Supporting Information). The σ CH →σ * CF and σ CH →σ * CN antiperiplanar interactions (4.6 and 2.9 kcal mol –1 , respectively) in the gauche orientation (i.e.…”

Quantum Chemical Modeling of Hydrogen Bonding in Ionic Liquids

“…The proper interpretation of NBO results has recently been under debate [37, 47, 103, 104]. Different population analysis methods are based on different computed properties, e.g.…”