A Semiempirical (AM1, MNDO, and MINDO/3) Study on the Thermolysis of 1-Alkynyl Ethers. Reaction Analysis by Correlation of Localized Molecular Orbitals

Article abstract of DOI:10.1021/jo00234a007

The thermolyses of ethoxyethyne (2a), isopropoxyethyne (2b), tert-butoxyethyne (2c), 1-ethoxy-1-propyne (3a), 1-isopropoxy-1-propyne (3b), 1-tert-butoxy-1-propyne (3c), and 1-ethoxy-1-butyne (4) leading to ketenes and olefins have been studied by means of the semiempirical SCF MO methods AM1, MNDO, and MINDO/3 at the RHF level.The reactions have been found in all cases to be concerted and to exhibit a highly synchronous character.The predicted order of reactivity, -CCO-t-Bu > -CCO-i-Pr > -CCOEt, fully coincides with the experimental one, the AM1 calculated activation entha lpies being the closest to the experimentally determined Arrhenius activation energies.Observed deuterium primary and secondary kinetic isotope effects are well reproduced by the calculation.A reaction analysis by correlation of localized molecular orbitals identifies the direction of flow of electron density along the reaction coordinate and suggests that the lack of adaptation of the ?-component of the initial triple bond to the geometrical changes taking place along the reaction path makes an important contribution to the activation energy of the reaction.