Conformational studies by dynamic nuclear magnetic resonance. Part 24. Gear effect in di-isopropyl-nitrosoamine and -phenyltriazene studied by carbon-13 nuclear magnetic resonance and molecular mechanics

Abstract

Evidence of the existence of correlated intramolecular orientation (gear effect) has been observed in Prⁱ₂NNO (1) and Prⁱ₂NNNPh (2) by ¹³C n.m.r. In the first case two conformers have been detected in a 92 :8 ratio at –120 °C. The corresponding activation parameters have been measured (ΔG^‡ 9.7 kcal mol^–1) and the structures of the two conformers assigned. Molecular mechanics calculations reproduce all the experimental observations and indicate, in addition, that this dynamic process is not synchronous but follows a two-step pathway. In the case of (2) the existence of the phenomenon could be detected through the interpretation of the selective broadening of one spectral line, and the free energy of activation could be measured (ΔG^‡ 10.2 kcal mol^–1) even though the spectrum of the less populated conformer was not directly detected.