Concept explainers
(a)
Interpretation: The product formed on thermal electrocyclic ring opening of the given compounds is to be predicted.
Concept introduction: Electrocyclic reactions involve ring opening or ring closure in a conjugated polyene. According to Woodward-Hoffmann rules, the polyene containing even number of bonds in thermal conditions undergoes reaction in conrotatory fashion and polyene containing odd number of bonds undergo reaction in disrotatory fashion.
Answer to Problem 25P
The product formed on thermal electrocyclic ring opening of the compound A is,
Figure 1
The product formed on thermal electrocyclic ring opening of the compound B is,
Figure 2
Explanation of Solution
The given compound A is,
Figure 3
Black coloured atoms have four bonds. So, these are the carbon atoms. The grey coloured balls have one bond. So, these are the hydrogen atoms. The molecular structure is,
Figure 4
The given compound undergoes thermal electrocyclic ring opening to form product with three pi bonds. According to Woodward-Hoffmann rules, the ring opening takes place in disrotatory fashion. The atomic orbitals of the carbon atoms whose sigma bond is broken rotates in opposite direction. The corresponding
Figure 5
The given compound B is,
Figure 6
Black coloured atoms have four bonds. So, these are the carbon atoms. The grey coloured balls have one bond. So, these are the hydrogen atoms. The molecular structure is,
Figure 7
The given compound undergoes thermal electrocyclic ring opening to form product with three pi bonds. According to Woodward-Hoffmann rules, the ring opening takes place in disrotatory fashion. The atomic orbitals of the carbon atoms whose sigma bond is broken rotates in opposite direction. The corresponding chemical reaction is shown below.
Figure 8
The products formed on thermal electrocyclic ring opening of the compound A and compound B is are shown in Figure 1 and Figure 2.
(b)
Interpretation: The product formed on photochemical electrocyclic ring opening of the given compounds.
Concept introduction: Electrocyclic reactions involve ring opening or ring closure in a conjugated polyene. According to Woodward-Hoffmann rules, the polyene containing even number of bonds in photochemical conditions undergoes reaction in disrotatory fashion and polyene containing odd number of bonds undergo reaction in conrotatory fashion.
Answer to Problem 25P
The product formed on photochemical electrocyclic ring opening of the compound A is,
Figure 9
The product formed on photochemical electrocyclic ring opening of the compound B is,
Figure 10
Explanation of Solution
The given compound A is,
Figure 3
Black coloured atoms have four bonds. So, these are the carbon atoms. The grey coloured balls have one bond. So, these are the hydrogen atoms. The molecular structure is,
Figure 4
The given compound undergoes thermal electrocyclic ring opening to form product with three pi bonds. According to Woodward-Hoffmann rules, the ring opening takes place in disrotatory fashion. The atomic orbitals of the carbon atoms whose sigma bond is broken rotates in opposite direction. The corresponding chemical reaction is shown below.
Figure 11
The given compound B is,
Figure 6
Black coloured atoms have four bonds. So, these are the carbon atoms. The grey coloured balls have one bond. So, these are the hydrogen atoms. The molecular structure is,
Figure 7
The given compound undergoes thermal electrocyclic ring opening to form product with three pi bonds. According to Woodward-Hoffmann rules, the ring opening takes place in disrotatory fashion. The atomic orbitals of the carbon atoms whose sigma bond is broken rotates in opposite direction. The corresponding chemical reaction is shown below.
Figure 12
The products formed on photochemical electrocyclic ring opening of the compound A and compound B is are shown in Figure 9 and Figure 10.
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Chapter 25 Solutions
ORGANIC CHEMISTRY
- Draw the product formed when each triene undergoes electrocyclic reaction under [1] thermal conditions; [2] photochemical conditions.arrow_forwardDraw all of the substitution and elimination products formed from thegiven alkyl halide with each reagent: (a) CH3OH; (b) KOH. Indicate thestereochemistry around the stereogenic centers present in the products,as well as the mechanism by which each product is formed.arrow_forwardWhat product is formed when each compound undergoes thermal electrocyclic ring opening or ring closure? Label each process as conrotatory or disrotatory and clearly indicate the stereochemistry around tetrahedral stereogenic centers and double bonds.arrow_forward
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- Ethylene oxide reacts readily with HO- because of the strain in the three-membered ring. Explain why cyclopropane, a compound with approximately the same amount of strain, does not react with HO-.arrow_forwardDraw all of the substitution and elimination products formed from the given alkyl halide with each reagent: (a) CH3OH; (b) KOH. Indicate the stereochemistry around the stereogenic centers present in the products, as well as the mechanism by which each product is formed.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-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_forward
