assignment5answers - CHM 3120 Assignment 5 Answers 1 Show...

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1 CHM 3120 Assignment 5 Answers 1. Show the missing products in the following sequence of reactions. Indicate whether the reactions are conrotatory or disrotatory. HOMO Ψ 3 H H A HOMO Ψ 4 A HOMO Ψ 3 B B H H h ν Disrotatory h ν Conrotatory Disrotatory 2. Identify the mode of ring closure or opening in the following. Are the hydrogens in the products syn or anti? h ν H H Me H H Me CH 3 CH 3 CH 3 CH 3 h ν O H H h ν O H H Me Me Me Me Me Me HOMO Ψ 3 HOMO Ψ 3 HOMO Ψ 5 HOMO Ψ 4 H H HOMO Ψ 3 HOMO Ψ 3 Me Me H H HOMO Ψ 2 HOMO Ψ 3 a) b) c) d) e) f) Disrotatory Disrotatory Disrotatory Conrotatory Conrotatory Disrotatory Disrotatory Disrotatory
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2 CH 3 CH 3 H H CH 3 H 3 C H 3 C CH 3 HOMO Ψ 2 HOMO Ψ 2 g) h) Conrotatory Conrotatory 3. Explain the formation of A and B. Identify the motion and give a name for each reaction. Identify the stereochemistry of the first and last compounds. HOMO Ψ 2 H H motion is conrotatory to get the cis-cis-trans product shown, must start with a cis fused compound cis HOMO Ψ 3 4 π electrocyclization 6 π electrocyclic reaction motion is disrotatory H H 4. The nucleophilic reactions of cyclopropanes involve S N 1-type displacements leading to the formation of open-chain products. OAc Cl OAc KOAc, HOAc KOAc, HOAc not formed a. Explain the above reaction by drawing a mechanism. Cl OAc OAc KOAc, HOAc + + - b. Is the opening in the reaction below conrotatory or disrotatory? Justify your answer. Cl KOAc, HOAc H 3 C CH 3 HOMO Ψ 1 opens by disrotatory motion +
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3 5. Ergosterol (derived from plants) is converted to Provitamin D 2 by a photochemical 6 π electrocyclic reaction. Give the structure of Provitamin D
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