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# Definition of the hydrogen bond (IUPAC Recommendations 2011)

## Details

**Authors** Arunan, E. and Desiraju, Gautam R. and Klein, Roger A. and Sadlej, Joanna and Scheiner, Steve and Alkorta, Ibón and Clary, David C. and Crabtree, Robert H. and Dannenberg, Joseph J. and Hobza, Pavel and Kjaergaard, Henrik G. and Legon, Anthony C. and Mennucci, Benedetta and Nesbitt, David J.

**Year** 2011

**Publisher** Pure and Applied Chemistry

**Kind of work** article

**Discipline** Chemistry

**Secondary disciplines** Physics

**Applied** false

[Read it at the publisher](https://doi.org/10.1351/PAC-REC-10-01-02) 
10.1351/PAC-REC-10-01-02

## In authors' words

### What they set out to do (purpose)

To replace earlier definitions of the hydrogen bond with one that reflects a century of theoretical and experimental knowledge and that requires evidence of bond formation.

### How they did it (methods)

An IUPAC task-group recommendation: a definition, six listed criteria that can serve as evidence of a hydrogen bond, and six typical characteristics.

### What they found (results)

The group defines the hydrogen bond as an attractive interaction between a hydrogen atom in a donor X–H group (X more electronegative than H) and an atom or group in the same or a different molecule, with evidence of bond formation. The criteria cover mixed electrostatic, charge-transfer and dispersion forces; a polarized covalent X–H bond; a near-linear X–H···Y angle; X–H lengthening with infrared red shift; NMR signatures; and a formation free energy above thermal energy. Interactions driven mainly by dispersion (for example CH4···CH4) are excluded, as is the antiparallel LiF dimer as a 'lithium bond'. Networks can show cooperativity, so properties are not purely pairwise additive. The authors note that borderline cases remain partly subjective and that satisfying more criteria makes the characterization more reliable.

## Commentary

### In short

An international chemistry committee redefines the hydrogen bond, specifying what must be present for an interaction to qualify, what is excluded, and what measurements count as evidence.

### Response

The definition is built mainly on a distinction: an interaction either meets the stated conditions (a polarized donor X–H, an electron-rich acceptor, attraction, evidence of bond formation) or falls outside them, as dispersion-dominated contacts do. It also specifies a relationship, the donor–acceptor interaction, with the strength and geometry of the X–H···Y contact tied to the properties of X–H. The observation that networks of hydrogen bonds show cooperativity, so that the whole is not a sum of pairs, bears on part–whole structure, but it appears as one listed characteristic and not as the organizing idea. The committee's candid note that borderline cases are subjective is relevant: the boundary is drawn by convention and evidence, not found. A perspective reading (infrared, NMR and electron-density topology as different vantage points on one bond) is possible but is not argued by the authors, so it is not claimed here.

**Patterns it shows** D, S, R

Shows the structure is there

**Added** 2026-11-02

**How to cite this** Arunan, E. and Desiraju, Gautam R. and Klein, Roger A. and Sadlej, Joanna and Scheiner, Steve and Alkorta, Ibón and Clary, David C. and Crabtree, Robert H. and Dannenberg, Joseph J. and Hobza, Pavel and Kjaergaard, Henrik G. and Legon, Anthony C. and Mennucci, Benedetta and Nesbitt, David J. (2011). Definition of the hydrogen bond (IUPAC Recommendations 2011). Pure and Applied Chemistry.