a. For conjugated systems with two, three, four, five,

Draw the product of each of the following reactions:

Draw the product of each of the following reactions:

Account for the difference in the products of the following reactions:

Show how norbornane could be prepared from cyclopentadiene.

Draw the product formed when each of the following compounds undergoes an electrocyclic reaction

Draw the product of each of the following reactions:

Could the reactions shown here take place by a concerted mechanism?

Which is the product of the following [1,3] sigmatropic rearrangement, A or B?

Dewar benzene is a highly strained isomer of benzene. In spite of its thermodynamic instability, it is very stable kinetically. It will slowly rearrange to benzene, but only if heated to a very high temperature. Why is it kinetically stable?

If the compounds shown here are heated, one will form one product from a [1,3] sigmatropic rearrangement and the other will form two products from two different [1,3] sigmatropic rearrangements. Draw the products of the reactions.

When the following compound is heated, a product is formed that shows an infrared absorption band at 1715cm-1 . Draw the structure of the product.

Two products are formed in the following [1,7] sigmatropic rearrangement, one due to hydrogen migration and the other to deuterium migration. Show the coni guration of the products by replacing A and B with the appropriate atoms (H or D).

a. Propose a mechanism for the following reaction. ( Hint: An electrocyclic reaction is followed by a DielsAlder reaction.) b. What would be the reaction product if trans -2-butene were used instead of ethene?

Explain why two different products are formed from disrotatory ring closure of (2 E, 4 Z, 6 Z )- octatriene, but only one product is formed from disrotatory ring closure of (2 E, 4 Z, 6 E )-octatriene.

Draw the product of each of the following sigmatropic rearrangements:

cis -3,4-Dimethylcyclobutene undergoes thermal ring opening to form the two products shown. One of the products is formed in 99% yield, the other in 1% yield. Which is which

If isomer A is heated to about 100 C , a mixture of isomers A and B is formed. Explain why there is no trace of isomer C or D.

Propose a mechanism for the following reaction:

Explain why compound A will not undergo a ring-opening reaction under thermal conditions, but compound B will.

A student found that heating any one of the isomers shown here resulted in scrambling of the deuterium to all three positions on the i ve-membered ring. Propose a mechanism to account for this observation.

How could this transformation be carried out using only heat or light?

Show the steps involved in the following reaction:

Propose a mechanism for the reaction shown here:

Problem 1P Examine the following pericyclic reactions. For each reaction, tell whether it is an electrocyclic reaction, a cycloaddition reaction, or a sigmatropic rearrangement.

Problem 2P Based on the lead compound for the development of procaine and lidocaine, propose structures for other compounds that you would like to see tested for use as anesthetics.

a. How many \(\pi\) MOs does 1,3,5,7-octatetraene have? b. What is the designation of its HOMO (\(\psi\)1, \(\psi\)2, etc.)? c. How many nodes does its highest energy \(\pi\) MO have between the nuclei? Equation Transcription: Text Transcription: pi 1,3,5,7 psi

Problem 4P Which compound is more likely to be a general anesthetic? CH3CH2CH2OH or CH3OCH2CH3

a. For conjugated systems with two, three, four, i ve, six, and seven conjugated \(\pi\) bonds, construct quick MOs (just draw the lobes at the ends of the conjugated system as they are drawn on pages \(1274\) and \(1275\) ) to show whether the HOMO is symmetric or antisymmetric. b. Using these drawings, convince yourself that the Woodward–Hoffmann rules in Table \(28.1\) are valid. Equation Transcription: Text Transcription: pi 1274 1275 28.1

Problem 6P a. Under thermal conditions, will ring closure of (2E, 4Z, 6Z, 8E )-2,4,6,8-decatetraene be conrotatory or disrotatory? b. Will the product have the cis or the trans configuration? c. Under photochemical conditions, will ring closure be conrotatory or disrotatory? d. Will the product have the cis or the trans configuration?

Which of the following are correct? Correct any false statements. a. A conjugated diene with an even number of double bonds undergoes conrotatory ring closure under thermal conditions. b. A conjugated diene with an antisymmetric HOMO undergoes conrotatory ring closure under thermal conditions. c. A conjugated diene with an odd number of double bonds has a symmetric HOMO.

a. Identify the mode of ring closure for each of the following electrocyclic reactions. b. Are the indicated hydrogens cis or trans?

Explain why maleic anhydride reacts rapidly with \(1,3\)-butadiene but does not react at all with ethene under thermal conditions. Equation Transcription: Text Transcription: 1,3

Problem 11P Show a mechanism for the formation of a benzodiazepine 4-oxide from the reaction of a quinazoline 3-oxide with methylamine.

a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions. b. Using arrows, show the electron rearrangement that takes place in each reaction.

a. Draw the product of the following reaction: If the terminal sp \(2\) carbon of the substituent attached to the benzene ring is labeled with \({ }^{14} \mathrm{C}\), where will the label be in the product? Equation Transcription: 14C Text Transcription: 2 ^14 C

Problem 14P Why was a deuterated compound used in the preceding example?

Account for the difference in the products obtained under photochemical and thermal conditions:

Problem 17P Explain why [1,3] sigmatropic migrations of hydrogen cannot occur under thermal conditions, but [1,3] sigmatropic migrations of carbon can.

Problem 18P a. Will thermal 1,3-migrations of carbon occur with retention or inversion of configuration? b. Will thermal 1,5-migrations of carbon occur with retention or inversion of configuration?

Does the [1,7] sigmatropic rearrangement that converts provitamin \(D_3\) to vitamin \(D_3\) involve suprafacial or antarafacial rearrangement?

Problem 20P Explain why the hydrogen and the methyl substituent are trans to one another after photochemical ring closure of provitamin D3 to form 7-dehydrocholesterol.

Chorismate mutase is an enzyme that promotes a pericyclic reaction by forcing the substrate to assume the conformation needed for the reaction. The product of the pericyclic reaction is prephenate, which is subsequently converted into the amino acids phenylalanine and tyrosine. What kind of a pericyclic reaction does chorismate mutase catalyze?

Convince yourself that the TE-AC method for learning the information in Tables \(28.1 , 28.3\) , and \(28.4\) is valid. Equation Transcription: Text Transcription: 28.1 , 28.3 28.4

Draw the product of each of the following reactions:

Draw the product of each of the following reactions:

Account for the difference in the products of the following reactions:

Show how norbornane could be prepared from cyclopentadiene.

Draw the product formed when each of the following compounds undergoes an electrocyclic reaction a. under thermal conditions. b. under photochemical conditions.

Draw the product of each of the following reactions:

Could the reactions shown here take place by a concerted mechanism?

Which is the product of the following [\(1,3\)] sigmatropic rearrangement, A or B? Equation Transcription: Text Transcription: 1,3

Dewar benzene is a highly strained isomer of benzene. In spite of its thermodynamic instability, it is very stable kinetically. It will slowly rearrange to benzene, but only if heated to a very high temperature. Why is it kinetically stable?

If the compounds shown here are heated, one will form one product from a [1,3] sigmatropic rearrangement and the other will form two products from two different [1,3] sigmatropic rearrangements. Draw the products of the reactions.

When the following compound is heated, a product is formed that shows an infrared absorption band at \(1715 \mathrm{~cm}^{-1}\). Draw the structure of the product. Equation Transcription: 1715cm-1 Text Transcription: 1715cm^-1

Two products are formed in the following [\(1,7\)] sigmatropic rearrangement, one due to hydrogen migration and the other to deuterium migration. Show the configuration of the products by replacing A and B with the appropriate atoms (H or D). Equation Transcription: Text Transcription: 1,7

a. Propose a mechanism for the following reaction. (Hint: An electrocyclic reaction is followed by a Diels–Alder reaction.) b. What would be the reaction product if trans -\(2\)-butene were used instead of ethene? Equation Transcription: Text Transcription: 2

Problem 36P Explain why two different products are formed from disrotatory ring closure of (2E, 4Z, 6Z )-octatriene, but only one product is formed from disrotatory ring closure of (2E, 4Z, 6E )-octatriene.

Draw the product of each of the following sigmatropic rearrangements:

cis -\(3,4\)-Dimethylcyclobutene undergoes thermal ring opening to form the two products shown. One of the products is formed in \(99%\) yield, the other in \(1%\) yield. Which is which? Equation Transcription: Text Transcription: 3,4 99% 1%

If isomer A is heated to about \(100^{\circ} \mathrm{C}\) , a mixture of isomers A and B is formed. Explain why there is no trace of isomer C or D. Equation Transcription: 100 °C Text Transcription: 100 degree C

Propose a mechanism for the following reaction:

Explain why compound A will not undergo a ring-opening reaction under thermal conditions, but compound B will.

A student found that heating any one of the isomers shown here resulted in scrambling of the deuterium to all three positions on the five-membered ring. Propose a mechanism to account for this observation.

How could this transformation be carried out using only heat or light?

Show the steps involved in the following reaction:

Propose a mechanism for the reaction shown here: