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The standard gaseous enthalpy of formation for methyl fluoride is estimated by five methods, all of which are in remarkable agreement with each other and which deviate significantly from the available experimental values. The suggested derived value is -225.4 + 3.2 kJ/mol. [1][2][3]. The value given in JANAF Tables [4], AfH~ F, g) = -234.3 + 29 kJ/mol, was based on the measured appearance energies ofCH3 + from CH3F and CH4 and has a large uncertainty. More recently, Lias, Karpas, and Liebman [5] have recommended At.H~ F, g) = -247 kJ/mol (no error bar was assigned), based on a photoionization mass spectrometry result for the threshold of gas-phase reaction 1 and on the enthalpy of formation of CH2 F § CH3F ~ CH2 F § + H + e- that fluorine has anomalous properties relative to the heavier halogens. In particular, the electron affinity of the fluorine atom and the homolytic dissociation energies of HF, CH3F, and the alkali fluorides are lower than they "should" be by ca. 109 kJ/mol (the range is about 20 kJ/mol for the most reliable measurements) when correlated with either the ionization potentials of the halogen atoms or the reciprocal of the relevant bond distances. About twice that destabilization is also found for the dissociation of F2 compared to the covalent dihalogens X2. It appears that fluorine species are destabilized relative to the chlorine, bromine, and iodine species by essentially a constant amount. We might expect similarly anomalous behavior of fluorine species in enthalpy-of-formation correlations with the other halogens. Indeed, plotting the enthalpies of formation of the hydrogen halides, the n-propyl and the isopropyl halides (the only alkyl fluorides for which there are experimental enthalpy-of-formation data [2]) against either (a) the ionization potentials of the halogen atoms or (b) the reciprocal of the diatomic halogen bond length shows in each case a linear correlation from which the fluorinecontaining molecule deviates. Screttas and Michel-Screttas [7] report that the enthalpies of formation of the mono-through the tetrahalomethanes and many other halogen-substituted compounds, R~R2R3CX, are linearly related to the respective sums of the ionization potentials of the halogen(s) and other groups, R i, in the molecule. Because the authors correlate a large data base of compounds, the deviation of each fluoride member from its congener series 65 10404)400/95/0200-0065507.50/0 ~r 1995 Plenum Publi~,hing Corlx~ration

Introduction: Scope of the Chapter, Definitions of Key Terms and Sources of Data Hydroxylamines and N ‐Substituted Derivatives O ‐Substituted Hydroxylamine Derivatives (Alkoxylamines) Monooximes Glyoxime and Other Dioximes Quinone Oximes and Nitrosoarenols Oxime Ethers Hydroxamic Acids and their Derivatives

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