Argon matrix trapping

It is worth noting, prior to citing actual metal atom studies, the recent secondary ion mass spectrometry (SIMS) on an argon matrix-isolated propene sample, demonstrating the applicability of SIMS analysis to the characterization of matrix-isolated species. The same group h s reported the first C NMR spectra of organic molecules trapped in an argon matrix. ... 

Species such as 5 and 6 are called benzynes (sometimes dehydrobenzenes), or more generally, arynes, and the mechanism is known as the benzyne mechanism. Benzynes are very reactive. Neither benzyne nor any other aryne has yet been isolated under ordinary conditions, but benzyne has been isolated in an argon matrix at 8 where its IR spectrum could be observed. In addition, benzynes can be trapped for example, they undergo the Diels-Alder reaction (see 15-58). It should be noted that the extra pair of electrons does not affect the aromaticity. The... 

Singlet halo(trifluoromethyl)carbenes [33a]-[33c], which were characterized by IR and UV spectroscopies and chemical trapping with HCl, have been generated from respective 3-halo-3-(trifluoromethyl)diazirines [34a]-[34c] frozen in an argon matrix at 12 K and irradiated with UV light at... 

The photolysis of phenyldiazirines [53a]-[53c] in an argon matrix was studied in a similar way. Intense bands of the corresponding carbenes [54a]-[54c] (Table 2) have been observed in all cases. The bands disappeared either when the matrix temperature was raised from 12 to 40-45 K (the corresponding stilbene bands appeared at the same time), or when a trapping agent (HCl, CI2) was doped into the matrix (Mal tsev et al., 1985b, 1987a). 

The allyl radical [115] trapped in an argon matrix can be photolytically (A = 410 nm) converted into the cyclopropyl radical [116] (Holtzhauer er a/., 1990). Dicyclopropane and cyclopropane were formed when the photolysed matrix was warmed from 18 to 35 K. The intermediate [116] was shown to be a cr-type (Cs symmetry) and not a rr-type symmetry) radical. Normal coordinate analysis of the radical [116] has been carried out and the IR band at 3118 cm has been assigned to the stretching vibration of the C—H bond at the radical centre. 

When anhydrous Na3P04 is vaporized at 1550-1650 K and the products are condensed in an argon matrix at ca. 10 K, the i.r. spectrum shows that the trapped... 

Stannylenes, the analogues of carbenes, are stabilized by sterically hindered groups such as mesitylene. Dimethylstannylene, a less stable species, was trapped in an argon matrix at 5 K and analysed by IR spectroscopy129. 

It was concluded from the formation of a dimer that 598 emerged by a DMS reaction in addition to a bicyclo[1.1.0]butane derivative [248]. The azacydoheptatetraene 599, trapped in an argon matrix kept at -261 °C, was observed by IR spectroscopy after photolysis of 3- and 4-diazomethylpyridine [249]. According to quantum-chemical calculations, the protodebromination of the respective bromodihydrodiazepi-nium ions is believed to proceed via the l,4-diaza-5,6-cycloheptadienes 600 and 601 as intermediates [169, 250],... 

All three compounds are prepared by elimination of bromine from the corresponding bridgehead-bridgehead dibromides. In the case of 3, this may be effected by butyllithium in a hydrocarbon solvent, but for 14 and 15 the elimination must be carried out by potassium vapor in the gas phase followed by trapping the product as an argon matrix at 10-15 K. 

Silabenzene (159) results from the flash pyrolysis of the silacyclohexadiene (158) and can be trapped in the argon matrix at 10 K (80AG(E)51, 80AGphotoelectron spectrum at 8.0 and 9.3 eV corresponding closely to those found for stibabenzene and for silatoluene (Scheme 248) (80JA429). 

IR spectroscopy is not confined to stable substances. In recent years, matrix isolation IR spectroscopy has become important in the investigation of short-lived, unstable molecular species. A gas containing such highly-reactive molecules - produced by photolysis of a reaction mixture, or in a high-temperature furnace - is suddenly cooled by contact with an inert solid (e.g. argon at c. 40 K). The matrix-isolated molecules are protected by the low temperature from unimolecular decomposition, and - by sheer isolation, if the dilution is sufficient - from bimolecular processes such as dimerisation or disproportionation. For example, the photolysis of Mn(CO)5H by a laser produces the otherwise unstable Mn(CO)5 and Mn(CO)4H molecules whose IR spectra can be measured in an argon matrix. Because of the low temperature, the lack of inter-molecular interactions and the rigidity with which the molecules are trapped in the matrix, such spectra are often very well resolved, better than can be achieved by conventional methods. Thus matrix isolation spectroscopy is widely used in the study of stable species, in preference to conventional techniques. 

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