Stereoelectronic control on the energy barrier to rotation about N-C (phenyl) bond

Abstract

Conformational analysis about the N-C (aryl) bond in <i style="mso-bidi-font-style:normal">N</i>-arylsuccinimidyl system incorporating different dissymmetric cages indicates that besides the steric and electronic interaction of <i>ortho-</i><span style="mso-bidi-font-style:italic">substituents<i>, </i>the dissymmetric cage also plays an important role in controlling the torsional barrier. In the case of anthracenemaleic

<span style="font-size:12.0pt;font-family:" times="" new="" roman";="" mso-fareast-font-family:"times="" roman";mso-ansi-language:en-in;mso-fareast-language:="" en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">anhydride adduct system, two stable rotamers about the N-C (phenyl) bond with 2'-methyl and 6'-ethyl substituents are isolated, whereas with such substituents rotamers are not isolable with cyclopentadiene-maleic anhydride and hexachlorocyclopentadiene-maleic anhydride (HCCPD-MA) adduct cages. X-ray crystallography of the HCCPD-MA system with two methyls at 2'-and 6'-positions in the phenyl ring (as in <b style="mso-bidi-font-weight: normal">5b</b>) demonstrats an orthogonal geometry of the aryl ring with respect to the succinimidyl plane. The <i>endo-</i>configuration of the adduct <b style="mso-bidi-font-weight:normal">5</b> has also been established.</span></span>