19719-81-4Relevant articles and documents
Transannular Interactions in Difunctional Medium Rings. 2. Molecular Structure and Conformational Properties of 1-Alkylhexahydroazocin-5-ones
Spanka, Gerhard,Boese, Roland,Rademacher, Paul
, p. 3362 - 3367 (1987)
Conformational properties of 1-alkylhexahydroazocin-5-ones 1-4 with a methyl, ethyl, isopropyl, or tert-butyl group as a substituent have been studied by He I photoelectron, 13C NMR, and IR spectroscopy as well as by MM2 and MNDO calculations.The molecular structure of the tert-butyl derivative 4 was determined by X-ray crystallography.Transannular interactions of the two functional groups in 1-4 have been determined from the first two ionization potentials with reference to the corresponding data of the respective monofunctional compounds.Since the ΔIP(n0) values of 1-4 are nearly identical, these molecules must have rather similar conformations. δ13C values of the carbonyl group in 1-4 show a systematic variation with substituent size, but this is probably caused by different solvation.From the IR spectra of 1 and 4 in the solid and liquid state and in solution it is concluded that phase transition is not accompanied by conformational changes.The eight-membered ring in 1-4 has a boat-chair conformation with the functional groups occupying positions with the shortest possible transannular distance (approximately 270 pm).It has been found difficult to determine the most stable conformation by theoretical methods, since transannular amide resonance is not treated correctly.For this interaction an energy of approximately 12 kJ/mol is estimated for 4 by comparison of experimental and calculated molecular structures.
Structural and Mechanistic Effects on the Rates of Ring-Opening Reactions in the 5-16-Membered-Ring Region
Cerichelli, Giorgio,Illuminati, Gabriello,Lillocci, Claudio
, p. 3952 - 3957 (2007/10/02)
Partial rate coefficients have been determined for the reaction of cyclic dimethylammonium ions with sodium methoxide in the 7-16-membered-ring region.Three second-order parallel reactions take place and lead to exocyclic demethylation (A), ring-opening substitution (B), and ring-opening olefin-forming elimination (C).The results were compared with the behavior of the five- and six-membered rings.Reaction A shows negligible dependence on ring size.In contrast, reactions B and C are affected by ring size through ring strain and geometry of the transition state: the latter factor is held responsible for major differences in the reactivity profiles between such reactions.
