- The Self-Reactions of 1-Methoxycarbonyl-1-methylethyl and Higher Ester Radicals: Combination vs Disproportionation and Oligomeric Products from Secondary Reactions
-
The geminate self-reactions of the title methyl, ethyl and butyl ester radicals (2a-c), formed by decomposition of the corresponding azo precursors (1a-c) in the presence of stable nitroxide radical scavengers, were found on the basis of product analysis to comprise combination and disproportionation in the ratios 56 : 44 (methyl), 58 : 42 (ethyl) and 47 : 53 (butyl).In the absence of radical scavengers, extensive oligomerization is observed.Hydrogenation and degradation were used in conjunction with g.l.c.-m.s. to deduce the identities of the dimeric, trimeric and tetrameric products, which were in most cases subsequently confirmed by isolation and n.m.r. analysis.Of particular interest is the highly regioselective disproportionation of radical (3) to give dimethyl 4-methylpent-1-ene-2,4-dicarboxylate (8), and the further reaction of (8) with (2a) to form branched oligomers (10) and (15).
- Bizilj, Snezna,Kelly, David P.,Serelis, Algirdas K.,Solomon, David H.,White, Kathleen E.
-
p. 1657 - 1673
(2007/10/02)
-
- Quantitative Evaluation of the gem-Dimethyl Effect on the Succinic Acid Anhydride Equilibrium. Conformations of the Acids and Anhydrides by Empirical Force Field Calculations
-
In order to evaluate quantitatively the gem-dimethyl effect on the succinic acid anhydride equilibrium, the conformations of succinic acid and its 2-methyl-, racemic 2,3-dimethyl-, tetramethyl-, and racemic 2,3-di-t-butyl-derivatives have been calculated by means of Allinger's 1977 empirical force field.An extension of the field was developed to calculate the conformations of the respective anhydrides.The calculated preferred conformations compare well with existing experimental data.No low-energy hydrogen-bonded minima for the acids were obtained.Increased substitution in the acids caused conformational changes facilitating ring closure: smaller torsion angles of conformations with gauche carboxy groups, favourable bond length and angle deformations, and a reduced number of preferred conformations.In the anhydrides, substitution leads to a twist around the C(2)-C(3) bond of the ring.The ΔΔH values estimated for the diacid anhydride equilibria agree well with experimental data in water indicating that the main cause of the observed gem-dimethyl effect in the anhydrides is relief of intramolecular strain arising on substitution in the acids.
- Ivanov, Petko M.,Pojarlieff, Ivan G.
-
p. 245 - 250
(2007/10/02)
-
