D. A. Evans Anomeric Effects in DNa Phosphodiesters Chem 206 Calculated Structure of ACG-TGC Duplex The Phospho-Diesters Excised from Crystal Structure Guanine The anomeric Effect Acceptor orbital hierarchy: 8 P-OR*>8P-0- R R R Gauche-Gauche conformation R Phosphate-2A Phosphate-2B Oxygen lone pairs may establish a simultaneous hyperconjugative relationship with both acceptor orbitals only in the illustrated Anti-Anti conformation Plavec, et al. (1996). How do the Energetics of the Stereoelectronic Gauche& Gauche-Gauche conformation affords a better donor-acceptor relationship Anomeric Effects Modulate the Conformation of Nucleos(t)ides? Pure Appl. Chem. 68: 2137-44O D. A. Evans Chem 206 Calculated Structure of ACG–TGC Duplex Adenine Thymine Cytosine Guanine Cytosine The Phospho-Diesters Excised from Crystal Structure Phosphate-1A Phosphate-1B Phosphate-2A Phosphate-2B 1B 2B The Anomeric Effect O P O O O R R Acceptor orbital hierarchy: * P–OR * > * P–O– Oxygen lone pairs may establish a simultaneous hyperconjugative relationship with both acceptor orbitals only in the illustrated conformation. – – P O O O R R – – O P O O O R – R – O P O O O R – R – Gauche-Gauche conformation Anti-Anti conformation Gauche-Gauche conformation affords a better donor-acceptor relationship Anomeric Effects in DNA Phosphodiesters Plavec, et al. (1996). “How do the Energetics of the Stereoelectronic Gauche & Anomeric Effects Modulate the Conformation of Nucleos(t)ides? ” Pure Appl. Chem. 68: 2137-44. 1A