Sarah Siska. C. A. Morales Ciekplak Model Chem 206 Anh's Calculated Transition State Energies Cieplak Model for Carbonyl Addition The model on-perpendicular attack similar to Anh-Eisenstein modification of the 15A6=90°.100110 Felkin model: stabilization of nucleophile via h2 Me a quadratic curve) Rn-105° assumes an electron-poor transition state L aligns best donor C-Xp anti to incoming nucleophile to stabilize o*of forming bond 163A a model generated rotate C-C bond by for optimum overlap Cieplak model STo-3G ab initio method (low level) Houk, Paddon-Row) disputed relkin. Anh importance of torsional effects Lowest energy transition states 0=107° σ*CNu Felkin Anh 、oCNu C 2-methylbutanal 2-chloropropanal C—X oC- (Felkin-Anh model (Felkin-Anh polar model Rs Structures are stabilized by stabilizing one of the fundamendal assumptions in frontier molecular orbital theory >2.7 kcal/mol Cieplak hypothesis is nonsense," ne Just because a hypothesis correlates a most stable Oc-Xd f'0 C-Nu set of observations doesn t make that ground state EFelkin model - EG1 Karabatsos conformed better donor DAE Anh. N. T. Eisenstein O. Tetrahedron Lett. 1976. 155 C-H>C-C>C-N>C-0 Cieplak, A S.J. Am. Chem 03.4540 Anh. N. T: Eisenstein. O. Nouv. J. Chim. 1977. 1. 61 (Houk disputes the Cieplak, A S; Tait, B D ; Je 111.8447 Anh, N. T. Top. Curr. Chem. 1980, 88, 14 ordering of C-H, C-C)Sarah Siska, C. A. Morales Ciekplak Model Chem 206 Et H Me H O Li H – Cl H Me H O Li H – RS RL RS RL R O RM R O M RM q = 107° Nu: X H Me H O Li H – O R R M Anh's Calculated Transition State Energies Anh, N. T.; Eisenstein, O. Tetrahedron Lett. 1976, 155 Anh, N. T.; Eisenstein, O. Nouv. J. Chim. 1977, 1, 61 Anh, N. T. Top. Curr. Chem. 1980, 88, 146 1.5 Å q q = 90°, 100°, 110° rotate C–C bond by 30° increments 1.63 Å 2-methylbutanal (Felkin-Anh model) 2-chloropropanal (Felkin-Anh polar model) The model: Lowest energy transition states: STO-3G ab initio method (low level) (interpolated using a quadratic curve) Karabatsos model Nu: 95 – 105° Non-perpendicular attack most stable ground state conformer a range of angles for optimum overlap >2.7 kcal/mol EFelkin model EG1 G1 C Nu s* C Nu H XD H RM/L O M Nu C XD C XD C XA C XA XD RS RM/L R O M s (Houk disputes the ordering of C–H, C–C) Cieplak Felkin Anh s s* s* s Cieplak, A. S. J. Am. Chem. Soc. 1981,103, 4540; Cieplak, A. S.; Tait, B. D.; Johnson, C. R. J. Am. Chem. Soc. 1989, 111, 8447 Cieplak Model for Carbonyl Addition - DAE Cieplak model Nu: • similar to Anh-Eisenstein modification of the Felkin model: stabilization of nucleophile via antiperiplanar C–XD bond • assumes an electron-poor transition state: aligns best donor C–XD anti to incoming nucleophile to stabilize s* of forming bond • a model generated to explain unexpected selectivities • importance of torsional effects (Felkin, Anh, Houk, Paddon-Row) disputed sC–Xd ↔ s*C---Nu C–H > C–C > C–N > C–O better donor "Structures are stabilized by stabilizing their highest energy filled states. This is one of the fundamendal assumptions in frontier molecular orbital theory. The Cieplak hypothesis is nonsense." "Just because a hypothesis correlates a set of observations doesn't make that hypothesis correct