Atomic hydrogen loss, detection

It should be indicated that the methylacetylene and propylene " are more complex reactants than the nonsubstituted counterparts and depict nonequivalent hydrogen atoms at the acetylenic and methyl group (methylacetylene) and at the vinyl and methyl group (propylene). Therefore, even the detection of the atomic hydrogen loss makes it difficult to elucidate if the hydrogen atoms are lost from the methyl group, the acetylenic/vinyl units, or from both positions. In these cases, it is very useful to conduct experiments with partially deuterated reactants J3-... 

The molecular ion appears to retain its cyclic structure, but several ions with two or three phosphorus atoms can be detected.192 The fragmentation patterns of a number of dialkylphosphines (157) show initial loss of an alkyl group as a neutral particle formed by the transposition of hydrogen.193 Some six-membered cyclic phosphites (158 X = OEt, OPh, or Cl) have been studied.194 The mass spectra of a wide variety of phosphine sulphides (159 Z = Ph, Me, CH2Ph, COPh, NH2, N=CHPh, or... 

All 60 C-atoms of Cjq are incorporated in the CgoHjo polycyclic aromatic hydrocarbon (PAH) 6, for which an efficient synthesis was developed [153], Laser irradiation of 6 at 337 nm induces hydrogen loss and the formation of CgQ, as detected by mass spectrometry (Scheme 1.6). Control experiments with C-labeled material and with the C48H24 homologue of 6 verified that the C50 is formed by a molecular transformation directly from the C50H30 PAH and not by fragmentation and recombination in the gas phase. 

Mass spectrometry is widely used in organometallic and cluster chemistry as a rapid means of determining the molecular weight, the number of carbonyl and other ligands present, and even the number of metal atoms present. In the case of relatively small molecules it is also possible to detect hydrogen loss. 

The structure —CHC1—CH2—CO—CH2 — was found by Kwei [99] in polyvinylchloride after photo-oxidation. Such j3 chloroketones decompose by the Norrish type I mechanism without loss of chlorine atoms. Hydrogen chloride is obtained only when polyvinylchloride is photo-oxidized above 30°C [98]. It seems that zipper dehydrochlorination plays little role in the reaction occurring on exposure to ultraviolet light at temperatures below 150°C in the presence of air [97], and that hydrogen chloride is mainly a product of thermal decomposition rather than photolysis [98], The following mechanism can be proposed which takes into account the experimental results namely, that chain scission and crosslinking occur simultaneously on irradiation at 253.7 nm [100] and that carbon dioxide is evolved, while an absorption band at 1775 cm-1 (ascribed to peracids) is detected in the infrared spectrum [98]. 

Another hydrogen atom lost from the a- or 0-Tetralinyl radicals forms either 1,2-dihydronaphthalene by reaction 1 or 1,2- and 1,4-dihydronaphthalene by reactions 2A and 2B. Loss of two more alkyl hydrogens forms naphthalene. The dihydronaphthalenes, which have been detected in low concentrations (6), were not observed under our experimental conditions. 

Irradiation of DAAN in benzene gives 3AN. This carbene reacts with oxygen very rapidly to give an intermediate believed to be the carbonyl oxide. The triplet carbene reacts with labeled a-methylstyrene to give the cyclopropane with total loss of stereochemistry (Table 6). Direct irradiation in neat isopropyl alcohol gives the ether in low yield (relative to the yields from XA, DMFL, FL, and BFL). The other products are those expected to result from hydrogen-atom abstraction. Triplet-sensitized irradiation of DAAN in the alcohol does not give a detectable amount of the ether. 

To select between these two alternative structures it was necessary to synthesize a labeled analog. Three hydrogen atoms of the methyl moiety of the ester group were substituted for deuterium. One of the principal pathways of fragmentation of [M N2]+ ions involves the loss of CH3 radical. Since all R substitutes in diazo ketones 4-1 were also methyls it was important to detect what group exactly is eliminated from the [M N2]+ ion. The spectrum of deuterated sample has confirmed that the methyl radical of the ester moiety leaves the parent ion. As a result the cyclic structure 4-2 was selected as the most probable. The ketene structure 4-3 is hardly able to trigger this process, while for heterocyclic ion 4-2 it is highly favorable (Scheme 5.22). 

For amines having an a-hydrogen atom, electrochemical oxidation leads to the imine as the first detectable intemrediate. In the absence of another nucleophile, this is not usually a useful reaction since the imine is hydrolysed by water present in the solvent leading to a mixture of products [80, 81], Oxidation of ten-butylamine, which has no a-hydrogen atom, leads to loss of a proton flrom the nitrogen atom and the dimerization of nitrogen centred radicals. The product isolated in moderate yields is azo-teri-butane 17 [82], The reaction can be carried out in an... 

The fate of the ejected electron was not discovered, and it seems possible that, if electrons were trapped, they would be captured by other molecules to give the corresponding radical anions, which should then certainly have been detected. There are certain fundamental objections to this postulate and it is suggested in Section V, F that the results are better in accord with simple homolysis resulting in the loss of hydrogen atoms from oxygen. 

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