Thermochemical determination of the structure of negative ions on the basis of data from resonance electron capture mass spectrometry. Phenol, its chlorinated derivatives and a thioanalogue

Appearance energies for [M - H](-) ions from phenol (I), 4-chlorophenol (II), pentachlorophenol (III) and pentachlorothiophenol (IV) were measured. The following thermochemical data were deduced from experiment: DeltaH(acid) values of 343.3, 335.7, 317.1 and 317.1 kcal mol(-1) for RH molecules (I, II, III, and IV, respectively) and electron affinities (EAs) of R(.) free radicals 2.55, 2.90, 3.79, and 3.65 eV, respectively. Our data for phenol (I) and 4-chlorophenol (II) demonstrate a higher stabilization of ArO(-) anions than was previously accepted. Using the enthalpic shift procedure for molecules and a series of isodesmic reactions for free radicals, earlier elaborated by the authors, a new Delta$bf H_bf fbf 0$ values for the following gas-phase species were obtained (kcal mol(-1)): C(6)Cl(5)Br (5.0), C(6)Cl(5)SH (8.5), p-ClC(6)H(4)C(.) (2. 0), C(6)Cl(5)C(.) (-15), C(6)Cl(5)S(.) (44). Copyright 2000 John Wiley & Sons, Ltd.     

Unexpected formation of the most strained δ-lactone in the pyrolysis of diethyl ester of cis-4-hydroxy-trans-5-methoxy-trans-1,2-cyclohexanedicarboxylic acid

Vacuum distillation of diethyl ester of cis-4-hydroxy-trans-5-methoxy-trans-1,2-cyclohexanedicarboxylic acid gave a single compound, 5-ethoxycarbonyl-7-methoxy-2-oxa[2.2.2.]bicyclooctan-3-one. The structure of this -lactone was demonstrated by data of NMR and IR spectroscopy. Calculations using the method of molecular mechanics showed that this structure has the highest steric strains of all possible stereoisomeric -lactones.M. V. Lomonosov Moscow State University, Moscow 119899. M. V. Lomonosov Moscow State Academy of Fine Chemical Technology, Moscow 117571. K. D. Ushinskii Yaroslavl' State Pedagogical University, Yaroslavl' 150000. Translated from Khimiya Geterotsiklicheskaya Soedinenii, No. 1, pp. 41–47, January, 1997.     

trans-2-Aminocyclohexanols as pH-triggers for conformationally controlled crowns and podands

Protonation of trans-2-aminocyclohexanols leads to dramatic conformational changes: due to an intramolecular hydrogen bond a conformer with equatorial position of ammonio- and hydroxy-groups becomes predominant. The trans-2-aminocyclohexanol moiety has been used for pH-induced conformational switching of a crown ether and a podand.     

Photoionization studies of substituted trimethylamines

Ionization energies of substituted trimethylamines (CH₃)₂NCH₂X, together with appearance energies of [M ? X]⁺ ions, have been measured by the photoionization technique. The heats of formation for the following radicals have been derived (in kJ mol^?1): C₂H₃^˙ (+ 314), Ph^. (+ 347), p-CH₃C₆H₄^˙ (+ 326), HC₂^˙ (+ 494), (CH₃)₂N?H₂ (+ 134), NC^˙ (+ 452), CF₃^. (? 435), (CH₃)₃Si^˙ (+ 54.5). The heats of formation obtained for [(CH₃)₂NCH₂]⁺ (+ 649) and (CH₃)₃Si⁺ (+ 610) lead to ionization energies of 5.35 eV for (CH₃)₂N?H₂ and 5.75 eV for (CH₃)₃Si^˙.