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  • Title: Conformational preferences and orbital interactions for methyl haloacetates.
    Author: Tormena CF, Yoshinaga F, Doi TR, Rittner R.
    Journal: Spectrochim Acta A Mol Biomol Spectrosc; 2006 Mar 01; 63(3):511-7. PubMed ID: 16359914.
    Abstract:
    Conformational preferences and orbital interactions of methyl chloroacetate (1), methyl bromoacetate (2) and methyl iodo-acetate (3) were analyzed using experimental infra-red data, theoretical calculations and NBO analyses. The conformational equilibria of compounds 1-3 can be represented by their cis and gauche rotamers. The gauche form of 1 is stable in the vapour phase and in a non-polar solvent, but the cis is predominant in a polar solvent. For 2 the gauche form is more stable than the cis, in both the vapour and liquid phases, but for compound 3 only the gauche form was observed both in vapour phase as in solution. These conformational preferences were attributed to the orbital interaction between two antibonding orbitals pi(C=O)(*)-->sigma(C-X)(*). This unexpected interaction was possibly due to the high (0.2) electron density on pi(C=O)(*), which results from the interaction between ether oxygen lone pair and pi(C=O)(*).
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