Interpretation:
The stereochemistry of the following pericyclic reactions,
a) The thermal cyclization of a conjugated tetraene.
Concept introduction:
a) A pericyclic reaction is a concerted reaction that proceeds through a cyclic transition state. Pericyclic reactions are completely stereospecific; that is, a single stereoisomer of the reactant forms a single stereoisomer of the product. Various kind of stereochemistry occurs in pericyclic reaction.
Interpretation:
The stereochemistry of the following pericyclic reactions,
b) The photochemical cyclization of a conjugated tetraene.
Concept introduction:
b) When like phases of the p orbitals are on the same side of the molecule, the two orbitals must rotate in opposite directions—one clockwise and one counterclockwise. Rotation in opposite directions is said to be disrotatory.
Interpretation:
The stereochemistry of the following pericyclic reactions,
c) A photochemical [4 1 4] cycloaddition.
Concept introduction:
c) When like phases of the p orbitals are on opposite sides of the molecule, the two orbitals must rotate in the same direction—both clockwise or both counterclockwise. Rotation in the same direction is said to be conrotatory.
Interpretation:
The stereochemistry of the following pericyclic reactions,
d) A thermal [2 1 6] cycloaddition.
Concept introduction:
d) A suprafacial stereochemistry occurs when like phases of the p orbitals of both reactants are on the same side of the pie system, so that two bonding interactions result.
Interpretation:
The stereochemistry of the following pericyclic reactions,
e) A photochemical [3, 5] sigmatropic rearrangement.
Concept introduction:
e) An antarafacial stereochemistry occurs when one pie system must twist to align like phases of the p orbitals of the terminal carbons of the reactants.
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Chapter 30 Solutions
Organic Chemistry
- The bicyclic alkene P can be prepared by thermal electrocyclic ring closure from cyclodecadiene Q or by photochemical electrocyclic ring closure from cyclodecadiene R. Draw the structures of Q and R, and indicate the stereochemistry of the process by which each reaction occurs.arrow_forwardIdentify the following pericyclic reaction; explain the course and stereochemistry of the reaction.arrow_forwarda) What product is formed from the [1,7] sigmatropic rearrangement of a deuterium in the following triene? (b) Does this reaction proceed in a suprafacial or antarafacial manner under thermal conditions? (c) Does this reaction proceed in a suprafacial or antarafacial manner under photochemical conditions?arrow_forward
- Predict the major products of the following reactions. Include stereochemistry whereapplicable.(a) 1@methylcycloheptene + BH3 # THF, then H2O2, OH-(b) trans@4,4@dimethylpent@2@ene + BH3 # THF, then H2O2, OHarrow_forwardUsing one or more of the following compounds as starting materials or products illustrate, with an example, each of the following type of pericyclic reactions. Your answer should include curved arrow mechanisms. (i) a disrotatory thermal electrocyclic reaction (ii) a conrotatory photochemical electrocyclic reaction (iii) a [4+2] cycloaddition (iv) a [3,3]-sigmatropic rearrangementarrow_forwardIdentify the following pericyclic reaction; explain the course, product distribution and stereochemistry of the reaction. Where the first product is produced 70% and the second product is produced 30%.arrow_forward
- The reaction of butan-2-ol with concentrated aqueous HBr goes with partial racemization, giving more inversion thanretention of configuration. Propose a mechanism that accounts for racemization with excess inversion.(b) Under the same conditions, an optically active sample of trans-2-bromocyclopentanol reacts with concentrated aqueous HBr to give an optically inactive product, (racemic) trans-1,2-dibromocyclopentane. Proposea mechanism to show how this reaction goes with apparently complete retention of configuration, yet withracemization. (Hint: Draw out the mechanism of the reaction of cyclopentene with Br2 in water to give thestarting material, trans-2- bromocyclopentanol. Consider how parts of this mechanism might be involved in thereaction with HBr.)arrow_forwardPredict the major products of the following reactions. Include stereochemistry whereapplicable.(a) 1@methylcycloheptene + BH3 # THF, then H2O2, OHarrow_forward1. (1-bromo-1, 3-dimethylcyclopentane) an optically active pure sample reacted with water. Write the complete mechanism which includes the electron-pushing arrows. Show the expected stereochemistry for each of the case and each mechanism should give two distinct products and then describe the relationship of the products to one another.arrow_forward
- Using the Woodward–Hoffmann rules, predict the stereochemistry of belowreaction. a thermal [5,5] sigmatropic rearrangementarrow_forwardQ3. For the following reactions, predict the products, mechanism and name all the products obtained Catalytic hydrogenation of cycloalkenes. Reduction of cyclohexanone with Zinc amalgam (Zn/Hg alloy) in concentrated hydrochloric acid Addition of CH2I2 in an alkene in the presence of Zn-Cu 2-hexene + chlorine gas Halogenation of cyclohexane in the presence of light and catalyst Sulfonation of Cyclobutane with oleum Addition of HBr to methylcyclopropanearrow_forwardDraw the product formed when diene M undergoes disrotatory cyclization. Indicate the stereochemistry at new sp3 hybridized carbons. Will the reaction occur under thermal or photochemical conditions?arrow_forward