[2], Sigma bond cleavage is most commonly observed in molecules, which can produce stable cations such as saturated alkanes, secondary and tertiary carbocations. The sigma bond breaks; hence this cleavage is also known as homolytic bond cleavage or α-cleavage. Higher-energy C-trap dissociation (HCD), EISA, and The cation has a radical on a heteroatom or an unsaturated functional group. NIST / TRC Web Thermo Tables, professional edition (thermophysical and thermochemical data) One of the most studied rearrangement reaction is the McLafferty rearrangement / γ-hydrogen rearrangement. The mass spectrum of toluene (methyl benzene) is shown below. [5] Prior to these experiments,[5][6] electrospray ionization in-source fragmentation was generally considered an undesired effect[7] however, electrospray ionization using Enhanced In-Source Fragmentation/Annotation (EISA) has been shown to promote in-source fragmentation that creates fragment ions that are consistent with tandem mass spectrometers. Toluene/water cluster ion fragmentation is studied for isolated cold clusters by means of one and two-color mass resolved excitation spectroscopy, time resolved pump (SI +-So) probe (1 <-SI) spectroscopy on the nanosecond time scale, and nozzlellaser delay timing experiments. During this reaction, γ-hydrogen will transfer to the functional group at first and then subsequent α, β-bond cleavage of the intermediate will take place. Sigma bond cleavage, radical site-initiated fragmentation, and charge site-initiated fragmentation are few types of simple bond cleavage reactions. A few different types of mass fragmentation are These reactions are well documented over the decades and fragmentation pattern is useful to determine the molar weight and structural information of the unknown molecule.
surface-induced dissociation (SID) using fast moving ions collision with a solid surface, The driving force of fragmentation is the strong tendency of the radical ion for electron pairing. This occurs when an alpha electron is removed. This occurs in the radical cations with unsaturated functional groups, like ketones, aldehydes, carboxylic acids, esters, amides, olefins, phenylalkanes.
Relative bond energy and the ability to undergo favorable cyclic transition states affect the fragmentation process. [3], Fragmentation can occur in the ion source (in-source fragmentation)[4][5] where it has been used with electron ionization[4] to help identify molecules and, recently (2020), with electrospray ionization it has been shown to provide the same benefit in facilitating molecular identification. [5][6] Tandem mass spectrometry generated fragmentation is typically made in the collision zone (post-source fragmentation) of a tandem mass spectrometer.
Fragmentation at this site produces a charged and a neutral fragment. Two major categories of bond cleavage patterns are simple bond cleavage reactions and rearrangement reactions. charge remote fragmentation.[8][9][10]. In the spectrum for toluene for example, the molecular ion peak is located at 92 m/z corresponding to its molecular mass. This term is also called inductive cleavage and is an example of heterolytic bond cleavage.
This is commonly observed in alcohols, ethers, ketones, esters, amines, alkenes and aromatic compounds with a carbon attached to ring. [2] Other rearrangement reactions include heterocyclic ring fission (HRF), benzofuran forming fission (BFF), quinone methide (QM) fission or Retro Diels-Alder (RDA). The fragments of a molecule cause a unique pattern in the mass spectrum. The molecular ion, again, represents loss of an electron and the peaks above the molecular ion are due to isotopic abundance. Peaks with mass less than the molecular ion are the result of fragmentation of the molecule. Fragmentation is a type of chemical dissociation, in which the removal of the electron from the molecule results in ionization. [2], Majority of organic compounds undergo simple bond cleavage reactions, in which, direct cleavage of bond take place. In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions formed from passing the molecules in the ionization chamber of a mass spectrometer. [2], Sigma bond cleavage also occurs on radical cations remote from the site of ionization. electron-transfer dissociation (ETD) through electron transfer between ions, The spectrum displays a strong molecular ion at m/e = 92, small m+1 and m+2 peaks, a base peak at m/e = 91 and an assortment of minor peaks m/e = 65 and below. [2], The driving force of charge site-initiated fragmentation is the inductive effect of the charge site in radical cations.
electron-capture dissociation (ECD) due to capturing of low energy electrons, EISA and collision-induced dissociation (CID) among other physical events that impact ions are a part of gas phase ion chemistry. [1][2] Fragmentation that occurs in tandem mass spectrometry experiments has been a recent focus of research as this data helps facilitate the identification of molecules. [2] This can take place by a process of homolytic cleavage/ homolysis or heterolytic cleavage/ heterolysis of the bond. collision-induced dissociation (CID) through collision with neutral molecule, Removal of electrons from either sigma bond, pi bond or nonbonding orbitals causes the ionization. electron-detachment dissociation (EDD), The C-C bond elongates and weakens causing fragmentation. laser induced dissociation which uses laser to induce the ion formation, In mass spectrometry, fragmentation is the dissociation of energetically unstable molecular ions formed from passing the molecules in the ionization chamber of a mass spectrometer.