Continuous concerted reorganisation of electrons, 5 major categories: Electrocyclic ring opening closure, cycloaddition, cycloreversion reactions, cheletropic reactions,. is the main content of the lesson chapter 10 "Pericyclic Reactions 周环反应". Invite you to consult. | Chapter 10 Pericyclic Reactions（周环反应） Pericyclic Reactions Continuous concerted reorganisation of electrons 5 major categories: Electrocyclic ring opening/closure Cycloaddition/cycloreversion reactions Cheletropic reactions (. carbene addition) Group transfer reactions (. H2 transfer) Sigmatropic rearrangements Sigmatropic Rearrangements Migration of a s-bond across a conjugated p-system [m,n] shift when the s-bond migrates across m atoms of one system and n of another Conjugated π Systems Suprafacial/Antarafacial Suprafacial migration: Group moves across same face Antarafacial migration: Group moves from one face to the other FMO Analysis [1,3] Sigmatropic Rearrangements: H migration FMO Analysis [1,3] Sigmatropic Rearrangements: C migration FMO Analysis [1,5] Sigmatropic Rearrangements Dewar-Zimmerman Dewar-Zimmerman model: Choose a set of 2p atomic orbitals and arbitrarily assign phase Connect the orbitals in the starting material Allow reaction to proceed according to . | Chapter 10 Pericyclic Reactions（周环反应） Pericyclic Reactions Continuous concerted reorganisation of electrons 5 major categories: Electrocyclic ring opening/closure Cycloaddition/cycloreversion reactions Cheletropic reactions (. carbene addition) Group transfer reactions (. H2 transfer) Sigmatropic rearrangements Sigmatropic Rearrangements Migration of a s-bond across a conjugated p-system [m,n] shift when the s-bond migrates across m atoms of one system and n of another Conjugated π Systems Suprafacial/Antarafacial Suprafacial migration: Group moves across same face Antarafacial migration: Group moves from one face to the other FMO Analysis [1,3] Sigmatropic Rearrangements: H migration FMO Analysis [1,3] Sigmatropic Rearrangements: C migration FMO Analysis [1,5] Sigmatropic Rearrangements Dewar-Zimmerman Dewar-Zimmerman model: Choose a set of 2p atomic orbitals and arbitrarily assign phase Connect the orbitals in the starting material Allow reaction to proceed according to postulated geometry and connect reacting lobes. Count number of phase inversions: Odd = Möbius, Even = Hückel Assign transition state as aromatic or antiaromatic based on number of electrons: Aromatic = Thermally allowed (Photochemically forbidden) Antiaromatic = Thermally forbidden (Photochemically allowed) System Aromatic Antiaromatic Hückel 4n + 2 4n Möbius 4n 4n + 2 Dewar-Zimmerman [1,3]-H shift [1,5]-H shift Suprafacial: Two Phase Inversions Hückel Topology Four electrons FORBIDDEN Suprafacial: Zero Phase Inversions Hückel Topology Six electrons THERMALLY ALLOWED Antarafacial: Three Phase Inversions Möbius Topology Four electrons ALLOWED Woodward-Hoffman A ground-state pericyclic change is symmetry-allowed when the total number of (4q+2)s and (4r)a components is odd. [1,5]-H shift – suprafacial [1,5]-H shift – antarafacial No. (4q+2)s = 1 No. (4r)a = 0 Total = 1 ALLOWED No. (4q+2)s = 1 No. (4r)a = 1 Total = 2 FORBIDDEN Woodward-Hoffman [1,7]-H shift – antarafacial [3,3] rearrangement .
