Electrostatic Potential Field and Nucleophilicity of 3, 5, 8, 10‐Tetramethyl‐aceheptylene

Abstract

The electrostatic potential (EP.) for aceheptylene (I) is calculated using a b -i d i o wavefunctions. I n addition, the EP. around I is approximated by a monopolc cxpression, using wavefunctions from various semiempirical procedures as a basis. It is found that the prcviously noted discrepancy between the theoretical prediction of differential nuclophilicity of the individual unsaturated C-atoms in 3,5,8,10-tetramethyl-accheptylene(II) and the experimental results of protonation is removed, if instead of local atomic charges, the EP. around 11, approximated by that of I is considered.

Molecular electrostatic potentials: an effective tool for the elucidation of biochemical phenomena.

“…that the C1-C2 region has the most negative potential associated with it and therefore should be the most likely target for electrophilic attack (37). This is in full accord with the experimental observation that protonation initially occurs exclusively at C1 or C2, even though the most stable final site for the proton is near C6, to which it eventually migrates (37,38).…”

“…[From the calculated atomic charges (37), protonation would incorrectly be predicted to occur at C4 or Cj.] Thus the electrostatic potential correctly reveals a key mechanistic feature of the reactivity of this molecule, the site of initial proton attack; this is not, however, the site that is favored thermodynamically.…”

Molecular Electrostatic Potentials: An Effective Tool for the Elucidation of Biochemical Phenomena

“…For instance, the electrostatic potential computed for acehepthylene (II) shows II 9 4 that the C1-C2 region has the most negative potential associated with it and therefore should be the most likely target for electrophilic attack (37). This is in full accord with the experimental observation that protonation initially occurs exclusively at C1 or C2, even though the most stable final site for the proton is near C6, to which it eventually migrates (37,38). [From the calculated atomic charges (37), protonation would incorrectly be predicted to occur at C4 or C9.]…”