Interpretation:
Ring opening reaction of the trans-cyclobutene isomer shown takes place readily at a lower temperature than a similar ring opening of the cis-cyclobutene isomer. This temperature effect is to be explained and the stereochemistry of each reaction, conrotatory or disrotatory, is to be identified.
Concept introduction:
An electrocyclic reaction involves the cyclization of a conjugated acyclic system. These reactions are reversible and are highly stereospecific.
In elecrocyclic reactions involving even number of electron pairs, a thermal reaction occurs in conrotatory manner and a photochemical reaction occurs in disrotatory manner.
In elecrocyclic reactions involving odd number of electron pairs, a thermal reaction occurs in disrotatory manner and a photochemical reaction occurs in conrotatory manner.
Want to see the full answer?
Check out a sample textbook solutionChapter 30 Solutions
Organic Chemistry
- The bicyclic alkene P can be prepared by thermal electrocyclic ringclosure from cyclodecadiene Q or by photochemical electrocyclic ringclosure from cyclodecadiene R. Draw the structures of Q and R, andindicate the stereochemistry of the process by which each reactionoccurs.arrow_forwardOH он toluene H OH 130 °C OH HO, ÓH Ph "Iarrow_forwardThe deuterated ethanol shown can be converted to an alkyl halide via a mesylate intermediate. Complete the mechanism, draw the final product (with nonbonding electrons) and select the correct absolute stereochemistry of the starting material and the final product.arrow_forward
- trans-Cyclooctene has been resolved, and its enantiomers are stable at room temperature. trans-Cyclononene has also been resolved, but it racemizes with a half-life of 4 min at 0°C. How can racemization of this cycloalkene take place without breaking any bonds? Why does trans-cyclononene racemize under these conditions but trans-cyclooctene does not? You will find it especially helpful to examine the molecular models of these cycloalkenes.arrow_forwardORGANIC CHEMISTRY Justify the stereoselectivity of the following Diel Alders intramolecular reaction:arrow_forward(a) When cis-1-bromo-2-methylcyclohexane undergoes an E2 reaction, two products (cycloalkenes) are formed. What are these two cycloalkenes, and which would you expect to be the major product? Write conformational structures showing how each is formed. (b) When rans-1-bromo-2-methylcyclohexane reacts in an E2 reaction, only one cyclo- alkene is formed. What is this product? Write conformational structures showing why it is the only product.arrow_forward
- The alkene shown undergoes bromination. (a) Draw the product(s) of bromination of this compound, including all expected stereoisomers (if any). Use wedge‑and‑dash bonds to designate the stereochemistry at any chirality centers, and make sure to draw an explicit hydrogen if a chirality center has one. (b) Characterize the starting alkene as having the E or Z configuration. (c) characterize the product(s).arrow_forwardWhen exactly 1 mole of methane is mixed with exactly 1 mole of chlorine and light is shone on the mixture, a chlorination reaction occurs. The products are found to contain substantial amounts of di-, tri-, and tetrachloromethane, as well as unreacted methane. Explain how a mixture is formed from this stoichiometric mixture of reactants, and propose mechanisms for the formation of these compounds from chloromethane.arrow_forwardIdentify the most stable, second most stable, and least stable conformation resulting from rotation about the bond indicated by the purple arrow. Assume, in this context, that the methoxy group is sterically smaller than the methyl group, an assumption that is supported by the fact that methoxy groups induce less axial strain than methyl groups in cyclohexane conformations. H H CH₂ CH₂ QOCH, HIC DOCH, HIC H₂C H₂C A Most stable Second most stable OCH₂ Least stable HH с H₂ OCH H₂C [Choose] [Choose] [Choose ] OCH₂ CH₂ D H₂C+ HH носна H₂C H₂C H H H OCH₂arrow_forward
- Define the Mechanism of the Radical Addition of HBr to an Alkene ?arrow_forwardA novel heterocyclic compound, M, contains nitrogen and sulfur atoms and exhibits interesting photochemical properties. When exposed to ultraviolet (UV) light at a specific wavelength, M undergoes a photoreaction resulting in two products: N and O. Product N is formed through a [2+2] cycloaddition involving the nitrogen atom in M, while product O results from a homolytic cleavage of a sulfur-sulfur bond in M. Given these reaction pathways, what is the most probable structure of M, and what are the likely structures of N and O? A. M is a thiazole derivative; N is a dimerized product through the nitrogen atoms, and O is a compound with two sulfur-centered radicals. B. M is a diazine derivative; N is a tetra-atomic cyclic compound, and O is a compound with two separate thiol groups. C. M is a thiadiazole derivative; N is a four-membered ring involving the nitrogen atom, and O results in two sulfur-centered radicals. D. M is a dithiolane derivative; N is a dimer involving the nitrogen…arrow_forwardDraw an approximate reaction-energy diagram showing the curves for the two possible pathways for ionic addition of HBr to 1-methylcyclohexene. (a) Formation of the major product, 1-bromo-1-methylcyclohexane, and (b) formation of the minor product, 1-bromo-2-methylcyclohexane. Point out how these curves show that 1-bromo-1-methylcyclohexane should be formed fasterarrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning