GAS-PHASE PYROLYTIC REACTIONS. PART 4. ARRHENIUS PARAMETERS AND HAMMETT ρ CONSTANTS IN GAS-PHASE ELIMINATIONS OF ALKYL PYRIDYL-, FURYL-, AND THIENYLCARBOXYLATE ESTERS

Article abstract of DOI:10.1016/S0040-4020(01)88383-6

The first-order rate coefficients ( 10⁵k/s^-1) of the gas-phase pyrolytic reactions of seven isopropyl (hetero)arylcarboxylate esters were calculated for 600 K to be: 75.34 for benzoate, and 100.0, 70.46, 94.03, 65.58, 100.9 and 120.2 for 2-thienyl-, 3-thienyl-, 2-furyl-, 3-furyl-, 3-pyridyl- and 4-pyridylcarboxylate, respectively.The corresponding Hammett replacement ρ⁰ substituent constants of the heterocyclic groups are: 0.53, -0.13, 0.42, -0.26, 0.55 and 0.88, respectively.The reported ρ⁰ constants are in agreement with other gas-phase and solution data, and are amenable to rationalization in terms of normal electronic and structural effects.Further, the physical constants of four new isopropyl heteroarylcarboxylate esters are described.