Concept explainers
(a)
Interpretation: The formation of both the isomeric products from the starting material by a sigmatropic rearrangement involving a
Concept introduction: In the sigmatropic rearrangement, the rearrangement of pi bond and the breaking of sigma bond take place. This results in the generation of new sigma bond in the product. In this type of rearrangement, the number of pi bonds remains constant in the reactant as well as in the product.
(b)
Interpretation: The reasons as to why
Concept introduction: In the sigmatropic rearrangement, the rearrangement of pi bond and the breaking of sigma bond take place. This results in the generation of new sigma bond in the product. In this type of rearrangement, the number of pi bonds remains constant in the reactant as well as in the product.
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ORGANIC CHEMISTRY
- 2) The Diels-Alder reaction, developed by German chemists Otto Diels and Kurt Alder (who received the Nobel Prize in 1950 for their discovery), has great synthetic importance due to the possibility of forming an unsaturated six-membered cycle without involving intermediates ionic. About the reaction, answer: (a) Indicate the reagents necessary for the synthesis of the following compounds, indicating who is the diene and who is the dienophile.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_forwardThe 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_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_forwardThe alkene shown undergoes bromination. H (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). (a) H Br₂ Draw the product(s) of bromination. Br H Brarrow_forwardThe bicyclic heterocycles quinoline and indole undergo electrophilic aromatic substitution to give the products shown. (a) Explain why electrophilic substitution occurs on the ring without the N atom for quinoline, but occurs on the ring with the N atom in indole. (b) Explain why electrophilic substitution occurs more readily at C8 than C7 in quinoline. (c) Explain why electrophilic substitution occurs more readily at C3 rather than C2 of indole.arrow_forward
- When treated with NaOH, the bromide below gives an alkene by the E2 mechanism, by elimination of the H atom indicated by the arrow: (a) Draw the Newman projection from which elimination takes place. (b) Draw the mechanism. (c) Draw the product with the proper stereochemistry. (d) Assign the proper stereochemical descriptor to the product. (e) Give the rate equationarrow_forwardIn some nucleophilic substitutions under SN1 conditions, complete racemization does not occur and a small excess of one enantiomer is present. For example, treatment of optically pure 1-bromo-1-phenylpropane with water forms 1-phenylpropan-1-ol. (a) Calculate how much of each enantiomer is present using the given optical rotation data. (b) Which product predominates—the product of inversion or the product of retention of configuration? (c) Suggest an explanation for this phenomenon.arrow_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_forward
- The bicyclic heterocycles quinoline and indole undergo electrophilic aromatic substitution to give the products shown. (a) Explain why electrophilic substitution occurs on the ring without the N atom for quinoline, but occurs on the ring with the N atom in indole. (b) Explain why electrophilic substitution occurs more readily at C8 than C7 in quinoline. (c) Explain whyelectrophilic substitution occurs more readily at C3 rather than C2 of indole.arrow_forwardIn some nucleophilic substitutions under SN1 conditions, complete racemization does not occur and a small excess of one enantiomer is present. For example, treatment of optically pure 1-bromo-1-phenylpropane with water forms 1-phenyl-1-propanol. (a) Calculate how much of each enantiomer is present using the given optical rotation data. (b) Which product predominates-the product of inversion or the product of retention of configuration? (c) Suggest an explanation for this phenomenon. H Br он H20 1-bromo-1-phenylpropane 1-phenyl-1-propanol observed [a) = +5.0 optically pure S isomer, [a] =-48 %3Darrow_forwardWhen (CH3)3C-C=C-H is treated with HCI, (CH3)2C(CI)C(CH3)C=CH₂ is formed as a minor product. Suggest a mechanism that would account for this transformation.arrow_forward
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