Halogenomethanes

Halogenomethanes. Several theoretical studies of the electronic structures of the halogenomethanes have been undertaken. SCF-MO calculations of the electric dipole moments and nuclear quadrupole coupling constants of a series of isoelectronic molecules including methyl chloride (FCl, HOCl, NH2CI, CH3CI) have been made and compared with the experimentally determined values. 

The carbon K, chlorine K, and chlorine Lu.m X-ray emission spectra of the chloromethanes CH Cl4 (0 r 3), the corresponding carbon and fluorine K, spectra of the fluoromethanes CH F4 (0 n 4), and the fluorine K absorption spectra of the fluoromethanes have been determined. The spectra of the fluoromethanes are said to complement recently obtained high-resolution U.P.S. of these molecules the chloromethane spectra are interpreted with the aid of the results of a theoretical analysis of their electronic structures. 

Several analyses of high-resolution gas-phase i.r. and Raman spectra of methyl halides, including those of CH3F, CHD2C1, CHgBr, and have been undertaken. The ground-state molecular geometry of 

A number of halogenomethanes have been subjected to other forms of molecular spectroscopy. High-resolution Stark spectra of several transitions of the V3 band of CH3F have been studied by means of a CO2 laser measurements of the hyperfine structure on certain rotational transitions in CH2F2 have been made using a molecular beam maser spectrometer the millimetre-wave spectrum of ground-state CDCla and the microwave spectrum of CD3I in excited vibrational states have also been observed. 

The application of molecular spectroscopic techniques to an elucidation of molecular reorientations and interactions of halogenomethanes in the liquid phase has been described. The usefulness of Raman spectroscopy in probing the details of molecular motion in liquids has been demonstrated for 

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Masuda Y, Yano I, Murano T. 1980. Comparative studies on the hepatotoxic actions of chloroform and related halogenomethanes in normal and phenobarbital-pretreated animals. J Pharmacobio-Dynamics 3 53-64. 

Clyne, M.A.A., Holt, PM. (1978) Reaction kinetics involving groundX2Yl and excited A2Z+ hydroxyl radicals. Part 2—Rate constants for reactions of OHX2Flwith halogenomethanes and halogenoethanes. J.Chem. Soc. Faraday Trans. 275, 582-591. 

This type of complexation is by no means limited to halogenomethanes, and the same behaviour is observed with aliphatic hydrocarbons such as isobutane [34], which shows a comparatively strong binding (Ka ca. 100 M-1) with host 38 under the same conditions as above (Fig. 11). It is interesting to note that in the isobutane complex, the upheld shift of the CH group (50-8c 4.25 ppm) is close to that of CHC13 (4.44 ppm) the structures of the two complexes are thus probably similar [35]. 

Morishima et al. (218-220) have continued their exhaustive study of the interactions of the nitroxide radical with a variety of closed-shell molecules. With proton donor molecules (X H) (e.g. CHCI3, CH2CI2) the low frequency shifts of the X-H proton and the high frequency shifts of the X portion are interpreted in terms of spin polarization of electron density from DTBN to X-H. Formation constants, enthalpies, and spin densities on the H and atoms for the H-bonded complex X H - DTBN have been evaluated. The spin delocalization mechanism involves positive spin density on DTBN being directly transferred on to the C-X antibonding orbital of the halogenomethane... 

Theoretical Studies. A total of seven theoretical analyses of the electronic structure of methane have been undertaken.67-73 In a number of these the results are compared with those for either the halogenomethanes CH F4 n(0s n 4),71,72 CH3C1,72 CH2C12,72 or the isoelectronic ions BH4 73 and NH1.73 The electronic structures of CF474 (in the isoelectronic series BeF4-, BF4, CF4) and CH3N075 have also been determined. 

It is thought that the halogenomethanes may remain at altitudes of 20—40 km for 40—150 yr and may well reach saturation values of 10—30 times the present levels. " According to Wofsy et aC the reduction in the ozone conentration in the stratosphere caused by the chloromethanes could be as much as 3% by 1980 and 16% by the year 2000, if the chloromethane consumption were to grow at the rate of 10% yr" Even if they were banned in 1990, the residual effect could be significant, and might endure for several hundred years. Other investigators, however, take a less pessimistic view (e.g. ref. 20). 

The formation of a peptide bond using tertiary phosphines and a halogenomethane has been studied in more detail. Trisamino-phosphines and carbon tetrachloride are the reagents of choice. Tripeptides are formed in high yield and with high optical purity. The simultaneous action of triphenylphosphine and carbon tetrachloride on the sulphonyl compounds (41), followed by triethylamine, gave iminophosphoranes (42). 

Interest in the photochemical generation and fate of acyl nitrenes has again been expressed. In benzoyl, p-methoxybenzoyl, and m-fluorobenzoyl azides, Curtius rearrangement of the photochemically generated acyl nitrenes to the corresponding isocyanates competes with formation of insertion products in halogen-free solvents.78 In halogenomethanes, the yields of isocyanates are... 

Some photoionizations occur only in halogenomethane solvents whereas in other solvents (e.g. ethanol, benzene) only fluorescence occurs in the halogenated solvents ionization is monophotonic. This is the case with di- and tetraphenyl-p-phenylenediamine in chloroform and carbon tetrachloride (Fitzgerald et al., 1971), and with TMPD in chloroform, bromoform, methylene bromide and chloride (Meyer, 1970), and dimethylaniline in bromobenzene (Gradowski and Latowski, 1974 et al., 1972). Electron transfer may occur from the excited aromatic singlet to ground state solvent [(54) and... 

Several papers have been published describing the reactions of halogenomethanes with halogens the systems which have been investigated are summarized in Table 13. The kinetics and mechanism of the reaction of atomic fluorine with CF3I and CCl3Br have been investigated in a fast-flow reactor. The analysis of the results proves conclusively that both reactions... 

Table 13 Summary of reactions of halogenomethanes with halogen atoms Halogen Halogenomethanes...

The kinetics of the reactions of chlorine atoms with a series of halogenomethanes have been investigated using mass-spectrometric techniques. The reactions of hot Br, produced by an (n, y) reaction with CHsBr, were studied in the presence of helium and krypton as moderators the results obtained were compared with those previously established for the formally analogous reaction between hot C1 and CH3CI. 

In a similar investigation, the interactions of the halogenomethanes CFgH, CH3F, and CH3CI with molecular iodine excited with 185 nm radiation have been studied in an attempt to elucidate the mechanisms of reactions of excited iodine molecules. ... 

In two communications, a group of Russian workers have summarized the enthalpies of formation and bond-rupture energies of all the halogenomethanes. These parameters are studied in relation to the number and type... 

Instructions for the conversion of polynuclear arenes (coronene, anthracene, decacyclene, naphthacene, naphthalene, pentacene, ovalene, 9,10-benzphenanthrene, 1,2-benzanthracene, 1,3,6,8-tetraphenylpyrene) into the corresponding perfluoro-alicyclic compounds and of 1,4-dichlorobenzene into perfluorocyclohexane by LaMar controlled-concentration direct-flow fluorination at room temperature and atmospheric pressure are now available in the patent literature, and precise details of the use of the method, in conjunction with a cryogenic reactor, to convert neopentane into perfluoroneopentane in low yield (10% after g.l.c. isolation) are also to hand. jhe results of kinetic studies on the direct fluorination of methane, [ H2]methane, halogenomethanes, and olefins are likewise in print. Treatment of the perfluoropropene dimers (CFsjsCiCF-CFs-CFs and trans-(CF3)2CF-CF -CF CFa with fluorine at —78 °C yields perfluoro-(2-methylpentane) quantitatively, while fluorination of a mixture of the trimers [(CFsjaCFlaC .CF-CFs and... 

Method using Base and a Substituted Halogenomethane. The influence of catalyst anions (as their tetrabutylammonium salts) and cations (as chlorides or bromides) on the generation of dichlorocarbene from chloroform-sodium hydroxide has been studied under standard conditions by determining the yield of dichloronorcarane produced from the addition of the carbene to cyclohexene. The presence of olefin appears to be necessary since in its absence only very slow decomposition of the trichloromethyl anion occurs. Dehmlow has also devised a new procedure for phase-transfer-catalysed cyclopropanation. Treatment of an alkene (or cycloalkene) with sodium trichloroacetate and a tetra-alkylammonium salt in chloroform without... 

Even in lipophilic solvents where hydrophobic effects and interactions are minimized, the cryptophanes strongly, reversibly and selectively complex neutral guests of complementary size such as the halogenomethanes. For example, enantio-selective complexation of CHFClBr by (140) has also been reported (138a). The water-soluble cryptophane (141) scavenges trace amounts of halogenomethanes from water. 

Kinetic studies on the static gas-phase thermal decomposition of the halogenomethanes CHFgCI (temperature range 434—S23 °C, initial reactant pressure 100—500 Torr) and CHF (437—515 C, 20—250 Torr) have established that the initial mechanistic step is a-eliraination of HX (X = Cl or Br) leading to difluorocarbene release, a reaction that has been put to preparative use in the synthesis of gem-difiuorocyclopropylsilanes [via flow copyrolysis of vinylchlorosilanes with chlorodifluoromethane at 485— 505 C (see p. 197)]. Fluoro-carbenes, -carbenoids, or -carbenoid complexes have also featured in several other pieces of work on the synthesis of halogenocyclopropanes [for example, see Schemes 29, 30 (olefins used... 

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