Heterolysis (chemistry) | EPFL Graph Search

In chemistry, heterolysis or heterolytic fission () is the process of cleaving/breaking a covalent bond where one previously bonded species takes both original bonding electrons from the other species. During heterolytic bond cleavage of a neutral molecule, a cation and an anion will be generated. Most commonly the more electronegative atom keeps the pair of electrons becoming anionic while the more electropositive atom becomes cationic. Heterolytic fission almost always happens to single bonds; the process usually produces two fragment species. The energy required to break the bond is called the heterolytic bond dissociation energy, which is similar (but not equivalent) to homolytic bond dissociation energy commonly used to represent the energy value of a bond. One example of the differences in the energies is the energy required to break a bond {| | H2 -> 2H. || || ΔH = 104 kcal/mol |- | H2 -> H+ + H- || || ΔH = 66 kcal/mol (in water) |} The discovery and categorization of heterolytic bond fission was clearly dependent on the discovery and categorization of the chemical bond. In 1916, chemist Gilbert N. Lewis developed the concept of the electron-pair bond, in which two atoms share one to six electrons, thus forming the single electron bond, a single bond, a double bond, or a triple bond. This became the model for a covalent bond. In 1932 Linus Pauling first proposed the concept of electronegativity, which also introduced the idea that electrons in a covalent bond may not be shared evenly between the bonded atoms. However, the ions had been studied before bonds mainly by Svante Arrhenius in his 1884 dissertation. Arrhenius pioneered development of ionic theory and proposed definitions for acids as molecules that produced hydrogen ions, and bases as molecules that produced hydroxide ions. The rate of reaction for many reactions involving unimolecular heterolysis depends heavily on rate of ionization of the covalent bond. The limiting reaction step is generally the formation of ion pairs.

C-C bond activation enabled by dyotropic rearrangement of Pd(iv) species

Qian Wang, Jieping Zhu, Hua Wu, Jian Cao

The weak carbon-metal bond combined with the kinetic inertness of the carbon-carbon bond renders metal-catalysed C-C bond activation to be highly challenging. Most of the reported C-C bond activation methodologies involve strain-releasing cleavage of small ...

NATURE RESEARCH2021

A catalytically active [Mn]-hydrogenase incorporating a non-native metal cofactor

Xile Hu, Farzaneh Fadaei Tirani, Matthew Wodrich, Huijie Pan

Nature carefully selects specific metal ions for incorporation into the enzymes that catalyse the chemical reactions necessary for life. Hydrogenases, enzymes that activate molecular H-2, exclusively utilize Ni and Fe in [NiFe]-, [FeFe]- and [Fe]-hydrogean ...

2019

Mechanistic study of the photo‐generation of hydrogen by decamethylruthenocene

Hubert Girault, Pekka Eero Peljo, Manuel Alejandro Méndez Agudelo, Heron Vrubel, Micheal Diarmaid Scanlon, Laurent Alexis Clément Vannay, Sunny Isaïe Maye, Lucie Josette Renée Rivier

Hydrogen evolution by decamethylruthenocene (Cp*2RuII) was studied in detail highlighting that metallocenes are capable of photo‐reducing hydrogen without the need of an additional sensitizer. Electrochemical, gas chromatographic and spectroscopic (UV/vis, ...

2019