Atom loss

Electrophilic Substitution. The most common mechanism for electrophilic attack at an aromatic system involves the initial attack of an electrophile to give an intermediate containing a tetrahedral carbon atom loss of, usually a proton, from the intermediate, then gives the product ... 

NPX ).(X=C1,F) while bromine atom loss is most significant in the... 

Aza (C -> N) Oxa (C —> 0) Abeo (general rearrangement) Cyclo (cyclic rearrangement) Iso (isomeric form) Seco (bond removal) Apo (side chain loss) De (functional group loss) Homo (add skeletal atom) Nor (skeletal atom loss)... 

Atom abstraction from the cr-carbon atom in spin adducts, which leads to nitrones, and thence in some instances to spin adducts of these nitrones (e.g. Scheme 9), is undoubtedly a general phenomenon. For this sequence to be observed it is necessary that some, or all, of the following conditions are fulfilled. (0 The nitrone is more reactive towards radical addition than is the original spin trap and/or the latter is substantially consumed in the reaction. (h) The initial spin adduct is particularly susceptible to hydrogen-atom loss (and probably reacts this way by disproportionation). ( 7) The secondary spin adduct is particularly persistent. 

Bertrand, M. Beynon, J.H. Cooks, R.G. Isotope Effects Upon Hydrogen Atom Loss from Molecular Ions. Org. Mass Spectrom. 1973, 7, 193-201. 

A comprehensive review of electrothermal atomization devices has been published (94). The review includes a discussion of commonly encountered problems such as atom loss through non-pyrolytic graphite, non-isothermal conditions, differences in peak height and peak area measurement, etc. 

A subsequent study examined phenylperoxy radical in greater detail. Fadden et identified five possible unimolecular decomposition pathways for phenylperoxy radical (Fig. 10) via oxygen atom loss to form phenoxy radical (Fig. 10, route A), via a dioxiranyl radical species (Fig. 10, route B), via a dioxetanyl radical... 

The oxidation pathways for alkylated heteroaromatics start with the formation of a radical species, via hydrogen atom loss or alkyl group homolytic bond cleavage. We calculated these BDEs for methyl- and ethyl-substituted derivatives of several key heteroaromatics (Tables 1-3). Few of these experimental values exist therefore. 

Table 1 Thermodynamic and spin density information for methyl hydrogen atom loss reactions of methyl-substituted heteroaromatic rings. Enthalpies and energies in kcal/mol, obtained at the B3LYP/6-31 l+G //B3LYP/6-31G (designated as B3LYP) and CBS-QB3 (designated as CBS) levels...

Fig. 17 Variation of reaction free energy (kcal/mol) with temperature (K) for alkyl C—H hydrogen atom loss in (a) five-membered ring methyl-substituted heteroaromatic rings and (b) six-membered ring methyl-substituted heteroaromatic rings.

Anglada, J. M., J. M. Bofill, S. Olivella, and A. Sole, Unimolecular Isomerizations and Oxygen Atom Loss in Formaldehyde and Acetaldehyde Carbonyl Oxides. A Theoretical Investigation, J. Am. Chem. Soc., 118, 4636-4647 (1996). 

The only identified reaction product of laser-ablated Mg atoms and acetylene under matrix isolation conditions is MgC=CH It was suggested that this reaction involves the insertion of excited-state Mg into the H—C bond to form an excited complex (equation 7), which then decomposes via H atom loss (equation 8). 

In a report by Hole et al, single crystals of 2 -deoxycytidine hydrochloride were investigated at 10 K using K-band (24 GHz) EPR, ENDOR and FSE spectroscopy.10 In this work, nine different radical products were identified and characterized. Three are one-electron reduced species (8,9 and 10), one each is formed by net hydrogen addition to C5 (11) and C6 (12). The remaining four are formed by net hydrogen atom loss from the 2 -deoxyribose moiety three of these (13—15) could be identified. 

Cleavage of amino acid esters occurs at both C— C bonds (a, b below) next to the nitrogen atom, loss of the carbalkoxy group being preferred (a). The aliphatic amine fragment decomposes further to give a peak at m/z 30. 

Fig. 1. Typical mass spectrum of S02 clusters taken at zero delay time between the pump and probe. Note the dominant intensity of the (SC>2)nSO+ series is due to an ion-state oxygen atom loss channel.

Fig. 10.19 The microwave frequency dependence of the n changing signals at low microwave power, where n changes up or down only by 1. Resonant multiphoton transitions are observed near the expected static field Stark shifted frequencies indicated. These resonances involve the absorption of four or five microwave photons. The down n changing atom production curve was obtained with the state analyzer field EA set at 50.0 V/cm, while up n changing was studied as n = 60 atom loss with EA = 45.5 V/cm. The locations of resonances for larger direct (not stepwise) changes in n are indicated along with...

For such unstable carbocations, an alternative approach to pAR can be developed, by recognizing the relationship that exists between pATR and pAa implied in Equation (15) (p. 30). For carbocations with [3-hydrogen atoms, loss of a proton normally yields an alkene. Then, as discussed by Richard, pATR and pAa form two arms of a thermodynamic cycle, of which the third is the equilibrium constant for hydration of the alkene, pAH2o, as already indicated in Scheme 1. The relationship between these equilibrium constants is shown for the t-butyl cation in Scheme 4. In the scheme the equilibria are... 

The behavior of two substituted organic acetamides (.V.iV-diethyl- and /V,/V-dipropyl-) were studied by ESR techniques. The spectra were characteristic of free radicals involving H-atom loss from the N-alkyl groups (297). 

Addition of oxygen atoms Loss of oxygen atoms... 

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