Die Verseifungsgeschwindigkeit von p‐Nitrophenetol

Blom, A. V.

doi:10.1002/hlca.19210040155

Cited by 3 publications

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“…These observations may easily be explained by the unfavorably high energy of the s-cis-ester Conformation. For example, in the case of methyl acetate [46], the measured value was found to be 8.5 kcal/mol higher than the value for the s-trans-form, and this value has been reproduced by 6-31 lG* calculations [47]. Bearing in mind that both ester groups of the molecule exist in the s-cis-conformation, the strain energy must be higher than 17 kcal/mol when compared to an open-chain 3-HB 'dimer'.…”

Section: Crystal Structures Of Rac-and Meso-diolide 1: Two Sorts O F mentioning

confidence: 99%

Preparation, Structure, and Properties of All Possible Cyclic Dimers (Diolides) of 3‐Hydroxybutanoic Acid

Seebàch¹,

Hoffmann²,

Kühnle³

et al. 1995

Helvetica Chimica Acta

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In connection with the proposed structure of a trans-membrane cellular ion channel consisting of a complex between poly[(R)-3-hydroxy butanoate] (P(3-HB)) and calcium polyphosphate, CaPPi (ca. 150 units each), which is supposed to contain s-cis-bonds or even more highly strained ester conformations, we have prepared and studied the properties of the cyclic dimer of 3-HB, the diolide 1. All possible forms of 1, the rac-, the meso-, and the enantiomerically pure (R,R)-and (S,S)-compounds were prepared, purified, and characterized. The synthesis (Scheme I ) started from dimethyl succinate with the key step being the Baeyer-Villiger oxidation of the rac-and meso-2,5-dimethylcyclohexane-1,d-diones 5. The rat-diolide 1 was resolved by preparative chromatography on a Chiralcel OD column (Fig. 1 ). The crystal structures of rue-1 (Fig. 3 ) and of meso-1 (Fig. 5 ) were determined by X-ray diffraction: the diolides 1 contain s-cis-ester bonds and an ester group with a conformation half way to the transition state of rotation (Fig.2). Strain energies for the diolides 1 of up to 17.8 kcal/mol are suggested. Accordingly, these compounds show reactivities similar to those of carboxylic-acid anhydrides or even acid chlorides. They cannot be chromatographed on silica gel, and they react with primary, secondary, and tertiary alcohols, and with amines to form derivatives of open chain 3-HB 'dimers', hydroxy acids 6, esters 7, and amides 8 (Scheme 2). The rate of acid-catalyzed ring opening of the diolides 1 with alcohols has been measured (Figs.6 and 7). From the results described, we conclude that it is unlikely for strained and reactive ester conformations to occur as part of ion channels through phospholipid bilayers of cells.

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Section: Crystal Structures Of Rac-and Meso-diolide 1: Two Sorts O F mentioning

confidence: 99%