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Conformational preferences of ?-fluoroketones may influence their reactivity.

ABSTRACT: Fluorine has been shown in many cases to impart specific and predictable effects on molecular conformation. Here it is shown that these conformational effects may have an influence on reactivity through studying the relative reactivity of various ?-halogenated ketones towards borohydride reduction. These results demonstrate that the ?-fluoro ketones are in fact a little less reactive than the corresponding ?-chloro and ?-bromo derivatives. It is suggested, supported by computation, that this effect is due to reactive conformations in which the C-X bond is orthogonal to the carbonyl group for good orbital overlap being disfavoured in the case of fluoro ketones.

SUBMITTER: Pattison G

PROVIDER: S-EPMC5753061 | biostudies-other | 2017

REPOSITORIES: biostudies-other

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Conformational preferences of α-fluoroketones may influence their reactivity.

Pattison Graham G

Beilstein journal of organic chemistry 20171229

Fluorine has been shown in many cases to impart specific and predictable effects on molecular conformation. Here it is shown that these conformational effects may have an influence on reactivity through studying the relative reactivity of various α-halogenated ketones towards borohydride reduction. These results demonstrate that the α-fluoro ketones are in fact a little less reactive than the corresponding α-chloro and α-bromo derivatives. It is suggested, supported by computation, that this eff ...[more]

PMID: 29564019

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Project description:Quantum mechanical calculations have been used to investigate how the incorporation of an amino group to the Cbeta- or Cgamma-positions of the pyrrolidine ring affects the intrinsic conformational properties of the proline. Specifically, a conformational study of the N-acetyl-N'-methylamide derivatives of four isomers of aminoproline, which differ not only in the beta- or gamma-position of the substituent but also in its cis or trans relative disposition, has been performed. To further understand the role of the intramolecular hydrogen bonds between the backbone carbonyl groups and the amino side group, a conformational study was also performed on the corresponding four analogues of (dimethylamino)proline. In addition, the effects of solvation on aminoproline and (dimethylamino)proline dipeptides have been evaluated using a self-consistent reaction field model, and considering four different solvents (carbon tetrachloride, chloroform, methanol and water). Results indicate that the incorporation of the amino substituent into the pyrrolidine ring affects the conformational properties, with backbone...side chain intramolecular hydrogen bonds detected when it is incorporated in a cis relative disposition. In general, the incorporation of the amino side group tends to stabilize those structures where the peptide bond involving the pyrrolidine nitrogen is arranged in cis. The aminoproline isomer with the substituent attached to the Cgamma-position with a cis relative disposition is the most stable in the gas phase and in chloroform, methanol and water solutions. Replacement of the amino side group by the dimethylamino substituent produces significant changes in the potential energy surfaces of the four investigated (dimethylamino)proline-containing dipeptides. Thus, these changes affect not only the number of minima, which increases considerably, but also the backbone and pseudorotational preferences. In spite of these effects, comparison of the conformational preferences, i.e., the more favored conformers, calculated for different isomers of aminoproline and (dimethylamino)proline dipeptides showed a high degree of consistency for the two families of compounds.

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Conformational preferences of ?-fluoroketones may influence their reactivity.

Publications

Conformational preferences of α-fluoroketones may influence their reactivity.

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