Determination of Thermodynamic Affinities of Various Polar Olefins as Hydride, Hydrogen Atom, and Electron Acceptors in Acetonitrile

Abstract

A series of 69 polar olefins with various typical structures (X) were synthesized and the thermodynamic affinities (defined in terms of the molar enthalpy changes or the standard redox potentials in this work) of the polar olefins obtaining hydride anions, hydrogen atoms, and electrons, the thermodynamic affinities of the radical anions of the polar olefins (X(•-)) obtaining protons and hydrogen atoms, and the thermodynamic affinities of the hydrogen adducts of the polar olefins (XH(•)) obtaining electrons in acetonitrile were determined using titration calorimetry and electrochemical methods. The pure C═C π-bond heterolytic and homolytic dissociation energies of the polar olefins (X) in acetonitrile and the pure C═C π-bond homolytic dissociation energies of the radical anions of the polar olefins (X(•-)) in acetonitrile were estimated. The remote substituent effects on the six thermodynamic affinities of the polar olefins and their related reaction intermediates were examined using the Hammett linear free-energy relationships; the results show that the Hammett linear free-energy relationships all hold in the six chemical and electrochemical processes. The information disclosed in this work could not only supply a gap of the chemical thermodynamics of olefins as one class of very important organic unsaturated compounds but also strongly promote the fast development of the chemistry and applications of olefins.

Unusual Reaction Constant for Hydride Transfer from a Carbanion to 9‐Arylxanthyliums

“…The observed reaction rate constants of hydride-transfer reactions in CH 3 CN (Scheme 1), the hydride affinities (ΔH H -A , defined as the molar enthalpy change in X and 9-GPhXn + to capture a hydride ion in acetonitrile) [8] of X and 9-GPhXn + , the standard one-electron oxidation potentials, and the standard one-electron reduction potentials of the corresponding species were determined. Detailed results are summarized in Tables 1, 2, and 3; see also Scheme 2.…”

Realization of Quantitative Estimation for Reaction Rate Constants Using only One Physical Parameter for Each Reactant

“…Since Δ G ≠o (XH) and Δ G ≠o (Y) contain not only kinetic composition but also thermodynamic composition, neither of Δ G ≠o (XH) and Δ G ≠o (Y) can be directly determined using one experimental method. However, from the definition formula of Δ G ≠o (XH) and Δ G ≠o (Y) (eqs 6 and 7), it is clear that if Δ G ≠ XH/X (activation free energy of self‐exchange HAT‐reaction for XH) and Δ G ≠ YH/Y (activation free energy of self‐exchange HAT‐reaction for Y) could be determined, Δ G ≠o (XH) and Δ G ≠o (Y) can be obtained, because the molar free energy changes of hydrogen atom donors (XH) to release hydrogen atoms, Δ G o (XH), and the molar free energy changes of hydrogen atom acceptors (Y) to accept hydrogen atoms in acetonitrile, Δ G o (Y), can be available . Thus, the remained work is just to determine Δ G ≠ XH/X values of various self‐exchange HAT‐reaction with XH or X in acetonitrile at 298 K.…”

“…In eqs 12–14, Δ G ≠ 3H/40 , Δ G ≠ 3H/39( t Bu) and Δ G ≠ 39( t Bu)H/40 are the activation free energies of the three different cross HAT‐reactions (eqs 9–11) in acetonitrile, respectively, which can be directly derived from the corresponding rate constants at 298 K according to Eyring equation, the latter can be determined by the stopped‐flow UV‐vis method (see Figures , and ); Δ G o 3H/40 , Δ G o 3H/39( t Bu) and Δ G o 39( t Bu)H/40 are the molar free energy changes of the three cross HAT‐reactions (eqs 9–11) in acetonitrile, respectively, which can be derived from our previous work …”

“…[a] Δ G o (XH) is the molar free energy change of XH to release hydrogen atoms in acetonitrile, which is derived from the corresponding Δ H o (XH) reduced by 4.9 kcal/mol . The values of Δ H o (XH) in acetonitrile were determined in our previous work, the unit is kcal/mol. [b] Δ G o (Y)=‐Δ G o (YH).…”

“…[c] Δ G o XH/40 is molar free energy changes of the HAT‐reactions, the data (kcal mol −1 ) of which are derived from the subtraction of the bond dissociation energy of two substrates (XH and 40H ): Δ G o XH/Y =Δ H o (XH) ‐ Δ H o ( 40H ), because the entropy change of the reactions with the type of XH+Y→X+YH in acetonitrile (Δ S o XH/Y ) has been verified to be or quite close to zero . The values of Δ H o (XH) and Δ H o ( 40H ) all can be derived from our previous publications …”