| Crystalline lithium trans-2-butenoate (1) undergoes a Michael addition upon irradiation with 60Co γ-rays. An X-ray structure determination of 1 revealed (a) that the head-to-tail arrangement of molecules in the crystal structure likely prevents the formation of a cyclodimer, and (b) the intermolecular arrangement is consistent with a radical chain mechanism proposed for the Michael addition. Introduction of formamide as an “extra” ligand results in a formamide “monosolvate” (2), with shorter distances between butenoates and greatly enhanced solid-state reactivity. Further consideration final step in the mechanism, would occur in a syn-fashion in 1, but in an anti-fashion in 2. In a mechanistic study using deuterium labeled trans-2-butenoates, the syn- and anti-additions were established. intermolecular, solid-state reaction is stereospecific and not the result of a random process.; The single-crystal to single-crystal ene reaction of hexaquamagnesium trans-2-butenoate dihydrate was studied in detail. Crystal structures at six different reaction stages for four individual crystals were solved; results were identical within experimental error. The reaction occurs as a “one-phase” process, with only small changes in cell constants and volume. Initial disorder of reactants (≈7:3), along with a corresponding product disorder and maximum product conversion of 76%, results in a complex four-component disorder.; A series of tetracarboxylatodicopper(II) species, Cu2(O 2CCH=CHCH3)Ln (n = 0,1,2), with L = formamide; acetamide; urea; N,N-diethylformamide, and pyridine were synthesized and structurally characterized. Changes of distances and alignments of trans-2-butenoate groups were readily achieved by changing the axial L groups. For n = 0, a complex that appeared to satisfy the geometric requirement for an ene reaction was obtained. However, upon heating, no ene reaction was observed for this complex or indeed any of the other materials, which is attributed to intermolecular steric factors.; New crystalline materials corresponding to the previously known sodium trans-2-butenoate (3) and potassium propionate ( 4) were successfully grown and structurally characterized. Both phases have crystal structures different from, but closely-related to, those previously studied. Consideration of the structures suggests that the new materials are polytypes, rather than polymorphs. If the polytypes of 4 could be isolated in sufficient quantities, the effects of polytypism on solid-state reactivity could be tested for the first time. (Abstract shortened by UMI.)... |
