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_forwardExplain [3,3] Sigmatropic Rearrangements ?arrow_forward
- Is 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 2,2-dimethylbutane is subjected to free-radical chlorination, ——— distant monochlorinated products are possible, and ——— of these products contain (s) asymmetric carbon atom.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_forwardWhat is the name of the following structure? хуба Br (3E,6Z)-7-bromo-4-fluoro-2,3,5-trimethyl-3,6-nonadiene (3Z,6Z)-7-bromo-4-fluoro-2,3,6-trimethyl-3,5-nonadiene (3E,6E)-7-bromo-4-fluoro-2,3,6-trimethyl-3,6-nonadiene (3Z,6E)-7-bromo-4-fluoro-2,3,6-trimethyl-3,5-nonadiene O (3Z,6E)-7-bromo-4-fluoro-2,3,6-trimethyl-3,6-nonadienearrow_forward23. For the alkenes shown below, consider the symmetry properties of the HOMO and the LUMO and decide whether this concerted cycloaddition reaction is likely to occur. CH2=CH2 CH2=CH2arrow_forward
- Answer the questions for 1,3,5-hexatriene, the conjugated triene containing six carbons. Select all that apply. 000000 Q00000 000000 Q00000 000000 000000 How many a molecular orbitals are there? O 3 Energy of the p atomic orbitals 器器 A2 00000 000000 a molecular orbitals Which a molecular orbitals are symmetric? Which t molecular orbitals are antisymmetric? T2 | T2 O T1 O O O O O O O O O Energy O O O O O Oarrow_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_forwardAssume that (2S,3R)-2-bromo-3-chloropentane has a specific rotation of +58°. What would be the specific rotation of the (2R,3S) isomer?arrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning