Sterically Congested Molecules, 6. Lone Electron Pair Donor Quality of the Imino Function: Increased Front Strain and Electronic Substituent Effects on Sterically Accelerated Nitrogen Inversion in Iminocyclopentanes

The p‐substituents of 2,6‐dimethyl‐N‐(2,2,5,5‐tetramethylcyclopentylidene)anilines are modified without interfering reactions at the CN double bond. The resultant series (5 – 8, 10 – 19) shows a strong (ca. —4.7 kcal/mol) steric acceleration of (E/Z) diastereotopomerization by front strain along the CN double bond but also the usual electronic substituent dependence, characterized by a Hammett s̀p– correlation (Q = +2.7). Conversely, the substituent constant for lithium at the p‐position of 7 may be estimated. The volume of activation is 1.5(8) cm3 mol–1 for 5. The π donor quality of the imino group corresponds to ca. 55 (±8)% of Pπ character as evaluated by spectral (13C NMR of 5 and 13, IR of 13) and reactivity data (of 13).