Interpretation:
Only the 2E,4E isomer is obtained in practice by opening of trans-3,4-Dimethylcyclobutene by two conrotatory paths to give symmetry-allowed products either (2E,4E)-2,4-hexadiene or (2Z,4Z)-2,4-hexadiene.
Concept introduction:
An electrocyclic ring-opening reaction is a reaction in which a σ bond of a cyclic reactant is cleaved to form a conjugated product with one more π bond. It occurs only when like phases of orbitals can overlap to form a bond. Such a reaction is symmetry allowed. It cannot occur between orbitals of opposite phase. Such a reaction is symmetry forbidden. To form a bond, the p orbitals on the terminal carbons must rotate so that like phases can interact to form the new sigma bond. Two modes of rotation are possible - When like phases of the p orbitals are on the same side of the molecule, the two orbitals must rotate in opposite direction one clockwise and one counterclockwise. Rotation in opposite directions is said to be disrotatory.
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.
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Chapter 30 Solutions
Organic Chemistry
- Show how to construct themolecular orbitals of a conjugatedcyclic system similar to benzene andcyclobutadienearrow_forwardExplain [3,3] Sigmatropic Rearrangements ?arrow_forwardThis reaction is also an important reaction of the tricarboxylic acid cycle in cells, wherein the reaction occurs in neutral solution, so the acid groups are both ionized to the carboxylate form. The reaction is catalyzed by the stereospecific enzyme fumarase that utilizes only the trans form of 2-butenedioate ion (also known as fumarate) and produces only the (S)-2-hydroxysuccinate enantiomer (also known as (S)-malate). Draw the correct stereochemical structures of these two compounds of the fumarase-catalyzed reaction. Be sure to include all hydrogen atoms and show the carboxylates as anions.arrow_forward
- The NMR spectrum of bromocyclohexane indicates a low field signal (1H) at δ 4.16. To room temperature, this signal is a singlet, but at -75 ° C it separates into two peaks of unequal area (but totaling one proton): δ 3.97 and δ 4.64, in ratio 4.6: 1.0. How do you explain the doubling in two peaks? According to the generalization of the previous problem, what conformation of the molecule predominates (at -75 ° C)? What percentage of the molecules does it correspond to? Solve all parts otherwise down vote and hand written solutionarrow_forward1-Chloro-1,2-diphenylethane can undergo E2 elimination to give either cis- or trans-1,2-diphenylethylene (stilbene). Draw Newman projections of the reactive conformations leading to both possible products, and suggest a reason why the trans alkene is the major product.arrow_forwardWhat is the best way to draw a molecular orbital diagram for 1,3-cyclopentadiene, identifying the Lowest unoccupied molecular orbital and the highest occupied molecular orbital?arrow_forward
- Answer the following question pertaining to the reaction of maleic anhydride and 1,3-butadiene: - Which conformation of 1,3-butadiene, s-cis or s-trans, is thermodynamically preferred and why?arrow_forward(2E,4Z,6Z,8E)-decatetraene has been cyclized to give 7,8-dimethy-1,3,5-cyclooctatriene. Predict the manner of ring-closure conrotatory or disrotatory for both thermal and photochemical reactions, and predict the stereochemistry of product in each case. Show how to get the answerarrow_forwardThere are a variety of isometric 1,2,3,4,5,6-hexachlorocyclohexanes, but one of them does not react with CH3CH2O- to give an elimation product. Provide the structures of this compound and briefly explain why it does not reactarrow_forward
- Determine all of the products obtained from the addition of HCl to the 1,3-diene. Once determined, draw a mechanism that accounts for the formation of every product. Then, Identify and account for the formation of the major adduct/or adducts under these conditions assuming that the reaction is conducted under thermodynamic conditions.arrow_forwardGiven that the change in free energy between axial and equatorial chlorine is 0.52 kcal.mol-1 , what is the difference in energy between the two chair conformations of 1,2,3,5-tetrachlorocyclohexane?What is the percent of the most stable chair conformation in solution at 298K?arrow_forwardWhat does the mechanism look like for 1,3-butadiene reacted with one mole of HBr to get 1-bromo-2-butene as a product?arrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning