The thermal decomposition of biallyl has been investigated from 977 – 1 070 °K at helium carrier gas pressures of 10–50 Torr. Under these conditions the rate of central C—C bond fission to give two allyl radicals can be measured without interference from secondary reactions. The reaction at the pressures employed is first order with respect to biallyl, but between first and second order in the total pressure. The temperature dependence of the rate constants, extrapolated to infinite pressure, and corrected to 298 °K, gives an activation energy of 45.7 kcal/mole for the reaction, corresponding to ΔH f (allyl) = 33.0 kcal/mole.
Abstract The structures of the m /z 87, [C 4 H 7 O 2 ] + , ions generated by dissociative ionization of CH 3 CGXCOOCH 3 and XCH 2 CH 2 COOCH 3 (X = CH 3 , Cl, Br, and I) have been investigated via their unimolecular and collisionally activated fragmentations and by apperance energy measurements. For both precursors loss of X = CH 3 produced, via H atom transfer, ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_2 = CH}\mathop {\rm C}\limits^{\rm + } \left({{\rm OH}} \right){\rm OCH}_{\rm 3} $\end{document} ( a ), Δ H f = 386 kj mol −1 . In marked contrast, loss of I ˙ from ionized CH 3 CHICOOCH 3 and ICH 2 CH 2 COOCH 3 proceeded without rearrangement to yield respectively ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_3}\mathop {\rm C}\limits^{\rm + } {{\rm HCOOCH_3}} $\end{document} ( b ), Δ H f = 480 kJ mol −1 and ( c ), Δ H f = 450 kJ mol −1 . These different fragmentation behaviours are explained via photoelectron spectra which show that the formal charge site in the precursor ion is at the carbonyl oxygen when X = CH 3 but at the halogen atom when X = I. The precursor molecules X = Cl and Br display both of the above characteristics, CH 3 CHXCOOCH 3 yielding mixtures of a and b and XCH 2 CH 2 COOCH 3 producing a and c ions.
Abstract The energetics of olefin loss from ionized alkyl phenyl ethers have been determined by ionization and appearance energy measurements. It is concluded that the reaction is governed by one or more of three features: (i) the strength of the bond between the phenoxy radical and the alkyl ion; (ii) the ease of isomerization of the alkyl ions, chiefly by H‐shifts therein, and (iii) the strength of the CH bond (primary, secondary and tertiary) involved in the H transfer to oxygen which precedes the olefin loss. The possible participation in the reaction of distonic ions and proton bound radical‐molecule pairs is also discussed.
Using an energy-resolved electron beam, ionization potentials for the following free radicals have been measured: vinyl 8.95 V, allyl 8.07 V, benzyl 7.27 V. For vinyl and allyl ions new measurements of thresholds for dissociative ionization give ΔH f (C 2 H 3 + ) = 266 kcal/mol and ΔH f (C 3 H 5 + ) = 226 kcal/mol, leading to neutral radical heats of formation ΔH f (C 2 H 3 ) = 59.6 kcal/mol and ΔH f (C 3 H 5 ) = 40 kcal/mol. The data for benzyl radical and ion give ΔH f (benzyl cation) = 213 kcal/mol.
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