130451-23-9Relevant academic research and scientific papers
The γ and δ effects of tin
Lambert, Joseph B.,Salvador, Lourdes A.,So, Jeung-Ho
, p. 697 - 703 (2008/10/08)
The trimethylstannyl group either γ (four bonds) or δ (five bonds) from a tosylate leaving group in the simple cyclohexane framework can alter the mechanism from nucleophilic assistance by solvent to intermediacy of a hyperconjugatively stabilized carbocation. The mechanistic change is indicated by rate accelerations (compared with the analogous ring lacking tin), by stereochemical dependence, by insensitivity to solvent nucleophilicity, by sensitivity to solvent ionizing power, by products resembling the hyperconjugative resonance structure, and (in the δ case) by the α-deuterium kinetic isotope effect. For the γ effect, stabilization of the carbocation occurs when tin is anti-anti to the leaving group (W geometry) and involves homohyperconjugation or cyclopropyl-(no-bond) conjugation. For the δ effect, stabilization occurs when tin is anti-gauche-anti (zigzag) to the leaving group and involves double hyperconjugation, i.e., (double-bond)-(no-bond) conjugation twice over. These results extend the concepts of delocalization of positive charge over σ bonds within the simple cyclohexane ring.
