Product of the photochemical cyclization of (2E,4Z,6E)-2,4,6-octatriene. Of (2E,4Z,6Z)-2,4,6-octatriene. Concept introduction: In photochemical reactions, the orbitals of the HOMO of the excited state to determine the course of the reaction. The excited state HOMO has the opposite orientation of the outermost p orbitals compared to the HOMO of the ground state. As a result, the method of ring closure of a photochemical electrocyclic reaction is opposite to that of a thermal electrocyclic reaction for the same number of pie bonds. Photochemical electrocyclic reactions occur in a conrotatory fashion for a conjugated polyene with an odd number of pie bonds.

Question

Treatment of propadiene (an allene) with hydrogen bromide produces 2-bromopropene as the major product. This suggests that the more stable carbocation intermediate is produced by the addition of a proton to Br HBr. H2C=C=CH, H3C CH2 a terminal carbon rather than to the central carbon. Propadiene 2-Bromopropene (a) Draw both carbocation intermediates that can be produced by the addition of a proton to the allene. (b) Explain the relative stabilities of those intermediates. Hint: Draw the orbital picture of the intermediates and consider whether the CH, groups in propadiene are in the same plane.

Answer 1

Question

Chapter 30.4, Problem 4P

Interpretation Introduction

Interpretation:

Product of the photochemical cyclization of (2E,4Z,6E)-2,4,6-octatriene. Of (2E,4Z,6Z)-2,4,6-octatriene.

Concept introduction:

In photochemical reactions, the orbitals of the HOMO of the excited state to determine the course of the reaction. The excited state HOMO has the opposite orientation of the outermost p orbitals compared to the HOMO of the ground state. As a result, the method of ring closure of a photochemical electrocyclic reaction is opposite to that of a thermal electrocyclic reaction for the same number of pie bonds.

Photochemical electrocyclic reactions occur in a conrotatory fashion for a conjugated polyene with an odd number of pie bonds.

Expert Solution & Answer

Trending nowThis is a popular solution!

See solution

Check out sample textbook solution

Students have asked these similar questions

Treatment of propadiene (an allene) with hydrogen bromide produces 2-bromopropene as the major product. This suggests that the more stable carbocation intermediate is produced by the addition of a proton to Br HBr. H2C=C=CH, H3C CH2 a terminal carbon rather than to the central carbon. Propadiene 2-Bromopropene (a) Draw both carbocation intermediates that can be produced by the addition of a proton to the allene. (b) Explain the relative stabilities of those intermediates. Hint: Draw the orbital picture of the intermediates and consider whether the CH, groups in propadiene are in the same plane.

5. What product would you expect to obtain from the Sy2 reaction of (S)-2-bromo- hexane with sodium acetate, CH3CO2Na? Show the stereochemistry of both product and reactant.

Why do cis-1-bromo-2-ethylcyclohexane and trans-1-bromo-2-ethylcyclohexane form different major products when they undergo an E2 reaction?