Argon matrix

THE cvcLOBUTADENE-TETRAHEDRANE SYSTEM. A related reaction is the photoisomerization of cyclobutadiene (CBD). It was found that unsubstituted CBD does not react in an argon matrix upon irradiation, while the tri-butyl substituted derivative forms the corresponding tetrahedrane [86,87]. These results may be understood on the basis of a conical intersection enclosed by the loop shown in Figure 37. The analogy with the butadiene loop (Fig. 13) is obvious. The two CBDs and the biradical shown in the figure are the three anchors in this system. With small substituents, the two lobes containing the lone electrons can be far... 

Thermal electrocyclizations of perhalogenated 1,3-butadienes yield perhalogenated cyclobutenes which can be solvolysed to 3,4-dihydroxy-3-cydobutene-l,2-dione ( squaric acid") and its derivatives (G. Maahs, 1966 H. Knorr, 1978 A.H. Schmidt, 1978). Double CO extrusion from fused cyclobutenediones has been used to produce cycloalkynes, e.g., benzyne from benzocyclobutenedione by irradiation in an argon matrix (O.L. Chapman, 1973) and cyc/o-Ci8, cyclo-Cn, etc. by laser desorption mass spectroscopy of appropriate precursors (see section 4.9.8). 

Oxygen Difluoride as a Source of the OF Radical. The existence of the OF radical [12061 -70-0] was first reported in 1934 (27). This work was later refuted (28). The OF radical was produced by photolysis of OF2 in a nitrogen or argon matrix at 4 K. The existence of the OF species was deduced from a study of the kinetics of decomposition of OF2 and the kinetics of the photochemical reaction (25,26) ... 

Gas Argon matrix Assignment Remarks concerning the approximate description of modes Assignment Gas ... 

Of much greater promise than thermolysis for the detection of oxirene is low-temperature photolysis. Strausz and coworkers (80JOC2271) investigated the photolysis, in an argon matrix at low temperatures, of 1,3-dioxolenone (vinylene carbonate 125). However, the only C2H2O species detected was ketene. The sulfur derivatives of (125), compounds (126) and... 

Particular attention has been given to the study of thermal rearrangements of N-substituted benzotriazoles. N-(N, N -Dialkylaminomethyl) benzotriazoles exist in the solid state solely as the isomers 37a, but in the liquid, solution, melt, and argon matrix phases they form equilibrium mixtures of the tautomers 37a and 3 (Scheme 19) [76JCS(P2)741 ... 

Photolysis of the 1,2,3-trithiole 42 in argon matrix (20 K) gave an electronic spectrum exhibiting the absorption maxima at 455 and 340 nm. Tlie spirodithiirane 43 and the thiosulfoxide 44 were believed to be responsible to these absorptions (89TL2955). 

Repeated attempts to obtain the band at 1030 cm 1 in spectra of the respective solids of various compositions did not furnish the desired result. Nevertheless, the band was observed in IR transmission spectra of gaseous components that separated from molten K2NbF7 and were collected in a standard gas phase cell with Csl windows appropriate for IR measurements. Fig. 85 presents the structure of the band and exact wave numbers of its components. Storage of the gas in the cell for several days resulted in a yellow deposit on the windows due to oxidation and subsequent separation of iodine. Analysis of available reported data [364 - 367] enables to assign the band observed at -1030 cm 1 to vibrations of OF radicals. It should be emphasized that a single mode was observed for OF in the argon matrix while in the case of nitrogen, two modes were indicated [367]. 

A recent study of the interaction of sodium with furan in an argon matrix at 4 °K32 has shown that the irradiation of the matrix with visible light (X = 550 run) induces the reaction... 

Four IR absorption bands have been identified in the spectrum of the hydroxysulfonyl radical (HOSO 2) which has been obtained by the reaction of hydroxyl radicals with sulfur dioxide in argon matrix at 11 K16. The observed bands at 3539.9 and 759.5 cm 1 have been assigned to O—H and S—OH stretching modes while the bands at 1309.2 and 1097.3 cm-1 have been assigned to the asymmetric and symmetric stretching modes of the double bonded S02 moiety. These data are consistent with the theoretical prediction on the geometry of the hydroxysulfonyl radical12. 

Fig. 12. Mossbauer spectrum of an argon matrix containing iron and nickel (59).

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. ... 

With respect to CO complexes, the luminescence spectra of a series of Group VI metal carbonyls and substituted carbonyls were obtained in frozen gas matrices at 12K. In addition, the IR spectra of HCo(CO>4 and HCo(CO)3 (proposed as an intermediate in hydroformylation) were observed in an argon matrix. ... 

These molecules must be regarded as essentially nonaromatic, although with some aromatic character. Tropolones readily undergo aromatic substitution, emphasizing that the old and the new definitions of aromaticity are not always parallel. In sharp contrast to 44, cyclopentadienone (46) has been isolated only in an argon matrix below 38 Above this temperature, it dimerizes. Many earlier attempts to prepare it were unsuccessful. As in 44, the electronegative oxygen atom draws electron to itself, but in this case it leaves only four electrons and the molecule is unstable. Some derivatives of 46 have been prepared. ... 

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... 

Infrared spectra of a carbene and the cyclopropane product have been observed in an argon matrix at 12-45 K. Carbenes in the triplet state react nonstereospecifi-... 

Raman spectra of S2 in its triplet ground state have been recorded both in sulfur vapor and after matrix isolation using various noble gases. The stretching mode was observed at 715 cm in the gas phase [46], and at 716 cm in an argon matrix [71]. From UV absorption and fluorescence spectra of sulfur vapor the harmonic fundamental mode of the S2 ground state was derived as t e = 726 cm . The value corrected for anharmonicity is 720 cm [26, 27]. Earlier reports on the infrared absorption spectrum of 2 in matrix isolated sulfur vapor [72] are in error the observed bands at 660, 668 and 680 cm are due to S4 [17] and other species [73]. 

Irradiation of disulfane in an argon matrix at 7.5 K by photons of wavelength 266 nm resulted in dissociation according to the following equations in an approximate 1 1 ratio [69] ... 

Cyclobutadiene owes its observed instability much to the kinetic property. Cyclobutadiene dimerizes in the argon matrix above 35 K [69] and only exists for 2-10 ms under low pressure [70, 71], However, cyclobutadiene is stabilized by bulky substituents (Scheme 30). The ferf-butyl derivative was quantitatively prepared even at a high temperature (130 °C) [72]. Yellow crystals of the cyclobutadiene fused by two seven-membered rings did not decompose below 240 °C [73]. 

Maier and co-workers condensed formaldehyde and elemental silicon at 12 K in an argon matrix and photolyzed the mixture to form silaketene H2SiCO, which is similar in structure to the silylene-CO adduct mentioned above. The reactants first form siloxiranylidene 49 (which equilibrates with an unknown species postulated as the planar/linear silaketene 50 when exposed to 313-nm-wavelength light) and then forms complex 51 when photolyzed at 366 nm (Scheme 15). This species could also be formed by photolyzing diazidosilane 52 in the presence of CO, and complex 51 equilibrates with SiCO (53) and H2. The CO infrared shift for this bent structure was calculated at 2129 cm , which is shifted —80cm from the calculated value of free CO, at 2210 cm. The experimentally observed value was reported at 2038-2047 cm at 12 K. 

Implicit in all this discussion of thermal reactions is the requirement that the moiety be stable enough in the solid state to last until reacting. The IR spectra of such partial molecules and their reactions have been observed for several cases. Rest and Turner 71) have shown that at 15° K the fragment Ni(CO)j is stable enough in an argon matrix to adopt its own characteristic symmetry (D3),). Reformation of the whole molecule occurs rapidly at 30° K. Similarly (70), Mn(CO)3NO and Mn(CO)2NO are stable in an argon matrix at 15° K and react to form Mn(CO)4NO at 30° K. In these cases, the fragmentation was induced photolytically so the dissociation products likely... 

UV irradiation (A>300nm) of an argon matrix containing tetra-fluoromethane led to the formation of difluorocarbene CF2 (Milligan and Jacox, 1968a). It was shown that the IR spectrum of this species contains three bands at 1222 (i i), 1102 (v ), and 668 (i 2)cm . Some time later difluorocarbene was stabilized in a neon matrix at 4.2 K from the gas phase after vacuum flash pyrolysis (1300°C) of perfluoroethene (Snelson, 1970b). In this case the IR bands of CF2 differed from those in an argon matrix by less than 2 cm . ... 

Dibromocarbene CBr2 has been formed in inert matrices by two different procedures. The reaction of CBr4 with lithium atoms in an argon matrix as well as the irradiation (with vacuum UV light) of a matrix containing tribromomethane HCBrs led to the appearance in the IR spectra of two bands of CBt2 at 595 and 641 cm . These absorptions were assigned, respectively, to the symmetrical and asymmetrical C—Br stretches. 

Cyclopropenylidene [2] has been obtained from two different precursors, [3] and [4], by their thermal decomposition in the gas phase (Reisenauer et al., 1984 Maier et al., 1987, 1989a). The subsequent UV photolysis (A = 313 nm and 254 nm) of this carbene in an argon matrix led to its isomerization to propargylene [5] and further to vinylidencarbene [6]. It should be noted that the carbene [5] was independently obtained by... 

Ethynylhydroxy carbene [13] has been obtained by photoreaction (A>400 nm) of a triatomic carbon cluster with water in an argon matrix and studied by IR spectroscopy (Ortman et al., 1990). Five frequencies were measured for [13] and a vibrational band at 1999.8 cm has been assigned to the C=C stretch. This value is more than 100 cmlower than the C=C stretching vibrations in acetylene derivatives, indicating that the C=C bond in the carbene [13] has lost some of its triple bond character. At the same... 

An attempt to measure the IR spectrum of the hydroxy carbene [28] after UV photolysis (A>220 nm) of formaldehyde isolated in an argon matrix was unsuccessful (Sodeau and Lee, 1978). Instead of [28] only hydroxyacetal-dehyde resulting from carbene insertion into the C—H bond of the starting formaldehyde was found in the reaction products. Due to its small size, the... 

During photolysis of [29] in an argon matrix doped with 4% CO, bands belonging to the ketene [31] were observed along with those of the carbene [30], Upon further warming to 40-45 K the carbene bands disappeared and were replaced with bands of the ketene [31], indicating a direct interaction of carbene (CF3)2C with CO. Photolysis of diazirine [29] in a matrix doped with 17% CO resulted in the appearance of only ketene [31] bands the carbene bands were not detected in this experiment. 

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