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
- Consider the reaction between (1S,3S)‑1‑chloro‑3‑methylcyclopentane and methanethiol in the presence of sodium hydroxide. (a) Draw the organic product and clearly indicate stereochemistry by showing the hydrogen on the chirality centers and using wedge and dash bonds. (b) Then analyze the stereochemistry of the product. racemic chiral achiral (1R, 3S) (1R, 3R) (1S, 3S)arrow_forwardtrans-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_forwardCompound (2E,4Z,6Z,8E)-2,4,6,8-decatetraene has been cyclized to give 7,8-dimethyl- 1,3,5- cyclooctatriene. Predict the manner of ring-closure-conrotatory or disrotatory-for both thermal and photochemical reactions and predict the stereochemistry of the product in each case. Show the outermost molecular orbital cyclizaion.arrow_forward
- Compound W, C8H₁7Br, and X, CgH₁7Cl, are products of the radical bromination (W), and chlorination (X), of 2,4-dimethylhexane. W and X are each chiral. W reacts readily in water to form a chiral substitution product Y, CgH17OH. Reaction of a single enantiomer of W produces a single enantiomer of Y as the only substitution product. X likewise reacts readily in water though at a slower rate than W; a chiral substitution product Z, C8H₁7OH, is again formed. Unlike w, however, reaction of a single enantiomer of X produces Z that is nearly racemic. Propose structures for W and X. 0 • Do not use stereobonds in your answer. In cases where there is more than one possible structure for each molecule, just give one for each. • Draw one structure per sketcher. Add additional sketchers using the drop-down menu in the bottom right corner. Separate structures with + signs from the drop-down menu. ● +▾ 99.8) ChemDoodleⓇ + v ChemDoodleⓇarrow_forwardIs the molecular orbital diagram of 1,3-butadiene the same as cyclopenta-1,3-diene? If so how come? Doesn't the latter have 5 p orbitals or will it technically only have 4?arrow_forwardWhen 2-bromo-3,3-dimethylbutane is treated with K+ −OC(CH3)3, a single product T having molecular formula C6H12 is formed. When 3,3dimethylbutan-2-ol is treated with H2SO4, the major product U has the same molecular formula. Given the following 1H NMR data, what are the structures of T and U? Explain in detail the splitting patterns observed for the three split signals in T. 1H NMR of T: 1.01 (singlet, 9 H), 4.82 (doublet of doublets, 1 H, J = 10, 1.7 Hz), 4.93 (doublet of doublets, 1 H, J = 18, 1.7 Hz), and 5.83 (doublet of doublets, 1 H, J = 18, 10 Hz) ppm 1H NMR of U: 1.60 (singlet) ppmarrow_forward
- When 2,2-dimethylbutane is subjected to free-radical chlorination, ——— distant monochlorinated products are possible, and ——— of these products contain (s) asymmetric carbon atom.arrow_forwardUse the Woodward Hoffmann rule {Σ(4q+2) + (4r)a} to determine if the following 1,3-dipolar cycloaddition is thermally or photochemically allowed.arrow_forward1)Chemistry students are taking an experimental course in organic chemistry at a public university. During an experiment involving conjugated dienes, some doubts arose when discussing the results obtained so far: (a) A student obtained two products from the reaction of 1,3-cyclohexadiene with Br2. His lab partner was surprised to get only one product from the reaction of 1,3 - cyclohexadiene with HBr. Explain these distinct results. (b) One student, seeing the discussion of colleagues, commented that she obtained two distinct products when reacting 1,3,5-hexatriene with HBr, with different yields just by changing the reaction temperature. Explain the results she obtained using reaction mechanism and based on kinetic and thermodynamic control involving conjugated dienes.arrow_forward
- 1,3,5,7-Cyclooctatetraene, CgHg, is an unusual hydrocarbon in that it reacts with exactly 2 equivalents of potassium to give A, CgHgK₂, which can be isolated as a white solid. A exhibits a single proton NMR signal. Draw the structure of A. 1,3,5,7-cycloctatetraene 2 K/THF C8H8K2 + H₂ A • Draw cations and anions in separate sketchers. Separate structures with + signs from the drop-down menu. ? n ChemDoodle®arrow_forwardShow that the [4 + 4] cycloaddition of two butadiene molecules to give cycloocta1,5-diene is thermally forbidden but photochemically allowedarrow_forwardFor each of the following reactions, (a) draw the HOMO of one reactant and the LUMO of the other, assuming that both reactants are in their ground state, and (b) illustrate the HOMO–LUMO interaction and determine if such an interaction leads to a thermally allowed or forbidden reaction.arrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning