Neuere Beiträge zur Chemie mittlerer Ringe

Huisgen, Rolf

doi:10.1002/ange.19570691102

Cited by 85 publications

(21 citation statements)

References 125 publications

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“…Table 10 summarizes the experimental dipole moments along with the MM3 and MM4 results. All MM4 dipole moments for carboxylic acids and esters are in fair agreement with experiment, 23,28,31,33,42,43,[47][48][49] except that for -caprolactone (chair). 49 The problem here is probably the experimental value, which was determined by polarization methods in solution.…”

Section: Moments Of Inertia and Dipolesupporting

confidence: 65%

“…All MM4 dipole moments for carboxylic acids and esters are in fair agreement with experiment, 23,28,31,33,42,43,[47][48][49] except that for -caprolactone (chair). 49 The problem here is probably the experimental value, which was determined by polarization methods in solution. The MM4 dipole moment rms error calculated from the microwave (Stark effect) values is improved from that of the MM3 from 0.135 to 0.024 D.…”

Section: Moments Of Inertia and Dipolesupporting

confidence: 65%

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Molecular Mechanics (MM4) Studies of Carboxylic Acids, Esters, and Lactones

Lii

2002

J. Phys. Chem. A

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MM4 force-field calculations have been extended to carboxylic acids, esters, and lactones. The related parameters were determined mainly by fitting to available experimental data and high-level ab initio calculations on simple molecules. The structures of the training-set molecules were well-reproduced with a rms errors of 0.005 Å for bond lengths and 0.8° for bond angles. The moments of inertia for 12 simple molecules of the title class were fit to the experimental (microwave) values with an overall rms error of 0.32%. The vibrational spectra were significantly improved from previous force-field calculations, with a rms error of 19 cm-1 for 74 frequencies of 5 compounds. The conformational equilibria and rotational barriers were also fit, approximately within experimental error. Although the calculated heats of formation for the carboxyl acids and esters were also improved relative to values in earlier work (MM3), the standard deviation of the heats for 30 selected compounds is still high (0.67 kcal/mol) compared to those for other classes of compounds previously studied with MM4.

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Section: Moments Of Inertia and Dipolesupporting

confidence: 65%

Section: Moments Of Inertia and Dipolesupporting

confidence: 65%

Molecular Mechanics (MM4) Studies of Carboxylic Acids, Esters, and Lactones

Lii

2002

J. Phys. Chem. A

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“…Properties of Lactones. In the 1950s, Huisgen and co-workers described detailed studies on lactones of different ring sizes to explain their deviating physical properties compared to their linear counterparts . In normal ring lactones (ring size 5−7), high dipole moments provide dipole interactions that rationalize their relatively high boiling points (see Table ).…”

Section: Resultsmentioning

confidence: 99%

Investigation of Lipase-Catalyzed Ring-Opening Polymerizations of Lactones with Various Ring Sizes: Kinetic Evaluation

et al. 2006

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Lipase-catalyzed ring-opening polymerizations of lactones with various ring sizes (6-to 13-and the 16-membered ring) employing Novozym 435 demonstrate fascinating differences in their polymerization rates. These differences cannot be related to variations in physical properties such as the dipole moment of the lactones only. For example, 10-decanolactone, 11-undecanolactone, and 12-dodecanolactone show dipole moments of around 1.9 D, but the initial rate constant of their Novozym 435-catalyzed polymerization was found to be 0.10, 0.38, and 4.91 h -1 , respectively. The Michaelis-Menten constants K M and V max were measured for all lactones, and this revealed that the K M was more or less independent of the ring size, suggesting similar affinities of the lipase for all lactones, while no obvious trend could be discerned for V max . However, conformational strain and transannular interactions present in medium ring lactones (ring size 8-12) affect the reactivity of these lactones in lipase catalysis in a similar way as was previously described for the alkaline hydrolysis of lactones, rationalizing the low reactivity of the 10-12-membered rings and the high reactivity of the 8-membered ring. To our surprise, there is a large discrepancy in lipase-catalyzed ring-opening polymerizations compared to the alkaline hydrolysis reactions with respect to the relative reactivity of lactones possessing a cisoid conformation of the ester bond: while the ratio in rates between δ-valerolactone and 12-dodecanolactone in a alkaline hydrolysis is 9400, the ratio in rates using Novozym 435-catalyzed polymerization is only 3. In fact, in the latter case lactones possessing a cisoid conformation are less reactive than large ring lactones possessing a transoid conformation. This mechanistic study also furnished polyesters with an increasing number of methylenes in their repeat unit. The polyesters can be readily prepared in reasonable molecular weights (>10 000 g/mol). Preliminary thermal characterization of the polyesters shows, as expected, that the melting temperature and the melting enthalpy increase with an increasing number of methylenes in the repeat unit.

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“…It is evident, however, that compounds 3 and 4 with a lactone structure are less nucleophilic than their acyclic and carbocyclic analogues 1 and 2 . It has long been known that small lactones are more acidic than the corresponding acyclic esters,13 because they cannot adopt the ( Z ) conformation, which is preferred by approximately 36 kJ mol –1 for methyl acetate (Scheme ) 14…”

Section: Resultsmentioning

confidence: 99%

Quantification of the Nucleophilic Reactivities of Cyclic β‐Keto Ester Anions

Corral-Bautista

Mayr

2015

Eur J Org Chem

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Keywords: Kinetics / Ion pairs / Anions / Enols / Reaction mechanismsKinetics of the reactions of enolate anions derived from acyclic and cyclic β-keto esters with benzhydrylium ions and quinone methides have been determined photometrically in dimethyl sulfoxide solution at 20°C. The reactions follow second-order rate laws: first-order with respect to the electrophile and first-order with respect to the enolate. Reactions conducted in the presence of 18-crown-6 ether and in the presence of variable concentrations of K + allowed the influ-

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Neuere Beiträge zur Chemie mittlerer Ringe

Cited by 85 publications

References 125 publications

Molecular Mechanics (MM4) Studies of Carboxylic Acids, Esters, and Lactones

Molecular Mechanics (MM4) Studies of Carboxylic Acids, Esters, and Lactones

Investigation of Lipase-Catalyzed Ring-Opening Polymerizations of Lactones with Various Ring Sizes: Kinetic Evaluation

Quantification of the Nucleophilic Reactivities of Cyclic β‐Keto Ester Anions

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