Margaret N. Mruzek

Low-energy, low-temperature mass spectra. XII. Identification of the isomers of the menthols and menthol methyl ethers by low-energy, low-temperature mass spectrometry

Abstract It is shown that it is possible to distinguish between menthol, isomenthol, neomenthol and neoisomenthol and their methyl ethers by measuring M + /[M-HOR] + (R = H for the menthols, R = Me for the ethers) at an electron ionizing energy of ca. 12 eV and at a source temperature of ca. 350 K. The low-energy, low-temperature mass spectra are reported.

Heavy atom kinetic isotope effects. Part 3.—The chlorine kinetic isotope effect in the gas-phase unimolecular decomposition of ethyl chloride

A study of 35k/37k for the gas-phase elimination of hydrogen chloride from ethyl chloride is reported. The value found at 723 K is 1.001 5 ± 0.000 2. Heavy atom kinetic isotope theory is applied in an attempt to characterise the transition state. It is concluded that there is only a moderate lengthening of the carbon-chlorine bond, and only a little motion of the chlorine atom in the transition state.

Chlorine kinetic isotope effects. Application of the transition state model to thermolysis of secondary and tertiary alkyl chlorides

Chlorine kinetic isotope effects in the thermolysis of 2-chloropropane and 2-chloro-2-methyl-propane have been measured at temperatures between 250 and 441 °C. The isotope effects are primary and they show normal temperature dependence. They increase with increasing methyl substitution on the central carbon atom. Model calculations using the heavy atom approximation theory show satisfactory agreement with the experimental data and with the observed temperature dependence. The participation of chlorine in the activated complex is the same for primary, secondary and tertiary alkyl chlorides and involves a combination of C—Cl stretching (3 %), C—C—Cl bending (2.7 %) and C—CH3 shortening (4 %) from the ground state values.

Chlorine kinetic isotope effects. Theramal decomposition of 1-chloroethane and evaluation of possible models of activated complex

Chlorine kinetic isotope effects have been investigated for the pyrolysis of 1-chloroethane in a static system in the temperature range 395–482°C. The temperature dependence of the kinetic isotope effects has been determined. The mass spectrometric isotope ratio analysis was made on the hydrogen chloride produced. A model for the chlorine involvement in the four-centre activated complex is advanced and various alternative geometries are evaluated in terms of heavy-atom approximation and first-order high temperature kinetic isotope effects. Best agreement with the experimentally determined values of k35/k37 is given by a model of the activated complex which involves chlorine participation in the reaction coordinate with three degrees of freedom. The effect of the individual geometric parameters that includes the C—Cl stretching, the C—C—Cl bending and the C—CH3 stretching and their combination, is evaluated.