Homolysis (chemistry)

Summary

In chemistry, homolysis () or homolytic fission is the dissociation of a molecular bond by a process where each of the fragments (an atom or molecule) retains one of the originally bonded electrons. During homolytic fission of a neutral molecule with an even number of electrons, two free radicals will be generated. That is, the two electrons involved in the original bond are distributed between the two fragment species. Bond cleavage is also possible by a process called heterolysis. The energy involved in this process is called bond dissociation energy (BDE). BDE is defined as the "enthalpy (per mole) required to break a given bond of some specific molecular entity by homolysis," symbolized as D. BDE is dependent on the strength of the bond, which is determined by factors relating to the stability of the resulting radical species. Because of the relatively high energy required to break bonds in this manner, homolysis occurs primarily under certain circumstances: Light (i.e. ultraviolet radiation) Heat Certain intramolecular bonds, such as the O–O bond of a peroxide, are weak enough to spontaneously homolytically dissociate with a small amount of heat. High temperatures in the absence of oxygen (pyrolysis) can induce homolytic elimination of carbon compounds. Most bonds homolyse at temperatures above 200°C. Additionally, in some cases pressure can induce the formation of radicals. These conditions excite electrons to the next highest molecular orbital, thus creating a singly occupied molecular orbital (SOMO). Adenosylcobalamin is the cofactor which creates the deoxyadenosyl radical by homolytic cleavage of a cobalt-carbon bond in reactions catalysed by methylmalonyl-CoA mutase, isobutyryl-CoA mutase and related enzymes. This triggers rearrangement reactions in the carbon framework of the substrates on which the enzymes act. Homolytic cleavage is driven by the ability of a molecule to absorb energy from light or heat, and the bond dissociation energy (enthalpy).

Official source

https://en.wikipedia.org/wiki/Homolysis_(chemistry)

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications (32)

Tuning the reactivity of uranium towards small molecules in multimetallic complexes

Nadir Jori

One of the main goals of organometallic chemistry in the last decades was the activation of small molecule in mild reaction conditions. Even though multiple examples of catalytic cycles able to produce fine chemicals from cheap and abundant sources using t ...

EPFL2023

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

Interfacial Effect between Aluminum-Based Complex Hydrides and Nickel-Containing Porous Carbon Sheets

Andreas Züttel, Emadeddin Oveisi, Heena Yang, Mo Li, Youngdon Ko

Supported aluminum-based complex hydrides (alanates) were investigated in view of their interaction at the interface. Nickel-containing porous carbon sheets (Ni-PCSs) were combined with various alanates, resulting in a decrease of the decomposition tempera ...

AMER CHEMICAL SOC2020

Related people (2)

Related units (7)

Related concepts (4)

In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes. A notable example of a radical is the hydroxyl radical (HO·), a molecule that has one unpaired electron on the oxygen atom. Two other examples are triplet oxygen and triplet carbene (꞉CH2) which have two unpaired electrons.

The bond-dissociation energy (BDE, D0, or DH°) is one measure of the strength of a chemical bond . It can be defined as the standard enthalpy change when is cleaved by homolysis to give fragments A and B, which are usually radical species. The enthalpy change is temperature-dependent, and the bond-dissociation energy is often defined to be the enthalpy change of the homolysis at 0 K (absolute zero), although the enthalpy change at 298 K (standard conditions) is also a frequently encountered parameter.

In chemistry, bond energy (BE), also called the mean bond enthalpy or average bond enthalpy is a measure of bond strength in a chemical bond. IUPAC defines bond energy as the average value of the gas-phase bond-dissociation energy (usually at a temperature of 298.15 K) for all bonds of the same type within the same chemical species. The bond dissociation energy (enthalpy) is also referred to as bond disruption energy, bond energy, bond strength, or binding energy (abbreviation: BDE, BE, or D).

Related courses (2)

This course will introduce students to the field of organic electronic materials. The goal of this course is to discuss the origin of electronic properties in organic materials, charge transport mecha

This course introduces modern computational electronic structure methods and their broad applications to organic chemistry. It also discusses physical organic concepts to illustrate the stability and

Related lectures (14)