Interpretation:
The stereochemistry of the following pericyclic reactions,
a) The thermal cyclization of a conjugated tetraene.
Concept introduction:
a) A pericyclic reaction is a concerted reaction that proceeds through a cyclic transition state. Pericyclic reactions are completely stereospecific; that is, a single stereoisomer of the reactant forms a single stereoisomer of the product. Various kind of stereochemistry occurs in pericyclic reaction.
Interpretation:
The stereochemistry of the following pericyclic reactions,
b) The photochemical cyclization of a conjugated tetraene.
Concept introduction:
b) When like phases of the p orbitals are on the same side of the molecule, the two orbitals must rotate in opposite directions—one clockwise and one counterclockwise. Rotation in opposite directions is said to be disrotatory.
Interpretation:
The stereochemistry of the following pericyclic reactions,
c) A photochemical [4 1 4] cycloaddition.
Concept introduction:
c) 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.
Interpretation:
The stereochemistry of the following pericyclic reactions,
d) A thermal [2 1 6] cycloaddition.
Concept introduction:
d) A suprafacial stereochemistry occurs when like phases of the p orbitals of both reactants are on the same side of the pie system, so that two bonding interactions result.
Interpretation:
The stereochemistry of the following pericyclic reactions,
e) A photochemical [3, 5] sigmatropic rearrangement.
Concept introduction:
e) An antarafacial stereochemistry occurs when one pie system must twist to align like phases of the p orbitals of the terminal carbons of the reactants.
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Chapter 30 Solutions
Organic Chemistry
- In 4+2 cycloaddition, ENDO stereochemistry is preferred because: endo stereochemistry allows the diene to adopt s-cis conformation. endo stereochemistry results in less steric hindrance. the transition state leading to endo stereochemistry is higher energy. it allows for additional π to π overlap between the diene and 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_forwardA student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C7H11Br. (a)Rank these three intermediates from most stable to least stable.arrow_forward
- Draw curved arrows and identify the thermal and photochemical products of the electrocyclic reaction of (2Z,4Z,6E)-octa-2,4,6-triene. Step 2: An electrocyclic reaction will undergo a concerted electron shift to form a cyclic ring. A new sigma bond will be formed between carbons 2 and 7. The product will be neutral. (2ZAZ,6E)-octa-2,4,6-triene Draw the curved arrows to show the mechanism. Select Draw Rings More Erasearrow_forwardDraw an approximate reaction-energy diagram showing the curves for the two possible pathways for ionic addition of HBr to 1-methylcyclohexene. (a) Formation of the major product, 1-bromo-1-methylcyclohexane, and (b) formation of the minor product, 1-bromo-2-methylcyclohexane. Point out how these curves show that 1-bromo-1-methylcyclohexane should be formed fasterarrow_forwardThe bicyclic alkene P can be prepared by thermal electrocyclic ring closure from cyclodecadiene Q or by photochemical electrocyclic ring closure from cyclodecadiene R. Draw the structures of Q and R, and indicate the stereochemistry of the process by which each reaction occurs.arrow_forward
- Consider the following chemical transformation:The transformation takes place via two sequential pericyclic reactions. Identify the two reactions and give a critical explanation whether the reactions are allowable or not. Explain the stereochemistryarrow_forwardQ6 Show how you would accomplish the follwoing transformations. (a) 2,2dibromobutane to but-1-yne (b) but-1-yne to oct-3-yne (c) trans-hex-2-ene to hex-2-yne (d) cyclodecyne to cis-cyclodecene (e) cyclodecyne to trans-cyclodecene (f) hex-1-yne to hexan-2-one, CH3COCH₂CH₂CH₂CH3 (g) hex-1-yn to hexanal, CH3(CH₂)4CHO (h) trans-hex-2-ene to cis-hex-2-enearrow_forwardFollowing is a balanced equation for bromination of toluene.(a) Using the values for bond dissociation enthalpies given in Appendix 3,calculate ∆H0for this reaction.(b) Propose a pair of chain propagation steps and show that they add up to theobserved reaction.(c) Calculate ∆H0for each chain propagation step.(d) Which propagation step is rate-determininarrow_forward1.What is the product of the reaction between 1,3-dibutene and bromoethene? (A) No reaction occurs (B) 4-bromocyclohexene (C) 3-bromocyclohexene (D) 3-bromocyclopentene 2. Cyclohexene undergoes hydrobromination. Which of these is a possible product? (A) Bromocyclohexane (B) All of these (C) Trans 1,2-dibromocyclohexane (D) Cis 1,2-dibromocyclohexane 3. A hydrocarbon molecule is saturated if the molecule contains (A) Single covalent bonds, only (B) A double covalent bond, only (C) A triple covalent bond (D) Single and double covalent bondsarrow_forwardarrow_back_iosSEE MORE QUESTIONSarrow_forward_ios
