Thermochemistry of organic and heteroorganic species. Part V. Photoionization studies of isomerization and fragmentation of polysubstituted cyclopropenes: 3-methyl-3-acetyl- and related compounds

Abstract

Appearance energies for molecular and some fragment ions from 3-methyl-3-acetyl-, 1,2-dimethyl-3-acetyl-, 1,2-dimethyl-3hydroxycarbonyl-and 1,3-dimethyl-2-(1-methyl)vinylcyclopropenes and model compounds 2,3-dimethylfuran and 1-methylindene were measured by photoionization mass spectrometry. It was shown that, in all cases, the structure of the [M-Me] + ion does not correspond to the expected structures of substituted cyclopropenium ions. Possible schemes for formation of [M-Me] + ions are given. Isodesmic reactions were systematically applied for calculation of the heats of formation for 35 possible C 5 H 5 O + isomers from 3methyl-3-acetyl-cyclopropene. In addition, the heats of formation for more than 30 other unsaturated ions and free radicals were estimated with the help of series of isodesmic reactions. A new value of 160 kJ mol-1 , as compared with the currently used value of 215.5 kJ mol-1 , for the cyclopropylmethyl free radical is suggested. The publication represents the further development of the methodology for the heat of formation estimation procedure for even-electron ions and free radicals.

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

“…However, from Scheme it is quite clear that the introduction of a stronger electron‐withdrawing (or more exactly more polarizable) group gives better stability to the less stable, in this case O‐centered, negative ion. In other words, the less stable ion (with more localized negative charge) extracts the higher stabilization effect from the same substituent compared with more stable ion species Similar tendencies were found previously for positive ions6–8 and free radicals 5,. 6 From Scheme we derive, by interpolation, the EA ( p ‐Cl 6 H 4 S · ) ≈2.8 eV.…”

“…To find out the unknown value of $$\Delta \hbox{H}_{\rm f}^{0} (\hbox{C}_{6}\hbox{Cl}_{5}\hbox{S}^{\cdot})$$ we used the series of isodesmic reactions which have been systematically applied to the thermochemistry of free radicals5–8 (Scheme , $$\Delta \hbox{H}_{\rm f}^{0}$$ and Q in kcal mol −1 given below; derived values—in square brackets):…”

Computational estimates of thermochemistry and pKavalues of cyclopropenyl imine superbases

“…The reactions RX 3A and RX 3B allow a check of the internal consistency of reports of the enthalpies of formation of the ions cyclopropenium and its methyl and trimethyl derivatives. The experimental value 1071 kJ/mol quoted by Domnin et al, is taken as a reference point . Then the formation enthalpy can be defined for methyl and trimethylcyclopropenium through isodesmic reactions RX 3A and RX 3B.…”

Thermochemistry of negatively charged ions. II. Energetics of formation of negative ions from acridanone and some of its derivatives

“…Á free radical with one benzene ring gives Q = 2.2 kcalÁmol À1 for the PhO Á → 2ÀNfO Á isodesmic reaction. 1,30 Further annelation of NfO Á radical with a benzene ring displays an attenuation effect 32 giving Q = 2.2 Â 0.7 = 1.54 kcalÁmol À1 . The final value for Q 1 (Eqn (13)) = 2.2 1.54 = 3.74 kcalÁmol À1 .…”

“…DH acid of 9-hydroxyanthracene was estimated using DDH acid 350.4 3 À 343.7 3 = 6.7 kcalÁmol À1 for phenol→ 1-hydroxynaphthalene and the suggested rule 32 of the attenuation effect Q 2 = 0.7Q 1 , upon further annelation or substitution in aromatic transition species like ions or free radicals. Hence, we get DDH acid = 6.7 Â 0.7 % 4.5 kcalÁmol À1 for 1-hydroxynaphthalene → 9-hydroxyanthracene and DH acid = 343.7À4.5 = 339.2 % 339 kcalÁmol À1 for the latter.…”