(a)
Interpretation: The product formed from the
Concept introduction: Sigmatropic rearrangements are pericyclic reactions which involve the migration of sigma bonds. In these reactions, old sigma bonds are broken and new sigma bonds are formed.
Curved arrows aid in determining the movement and flow of electrons in the reaction. The electrons that take part in the
(b)
Interpretation: If the given reaction proceeds in a suprafacial or antarafacial manner under thermal conditions is to be predicted.
Concept introduction: Sigmatropic rearrangements are pericyclic reactions which involve the migration of sigma bonds. In these reactions, old sigma bonds are broken and new sigma bonds are formed.
Curved arrows aid in determining the movement and flow of electrons in the reaction. The electrons that take part in the chemical reactions are shown by the curved arrows.
(c)
Interpretation: If the given reaction proceeds in a suprafacial or antarafacial manner under photochemical conditions is to be predicted.
Concept introduction: Sigmatropic rearrangements are pericyclic reactions which involve the migration of sigma bonds. In these reactions, old sigma bonds are broken and new sigma bonds are formed.
Curved arrows aid in determining the movement and flow of electrons in the reaction. The electrons that take part in the chemical reactions are shown by the curved arrows.
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Chapter 27 Solutions
PKG ORGANIC CHEMISTRY
- The 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(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_forwardGive the structure, exclusive of stereochemistry, of the principal organic product formed on reaction of 2,3-dimethyl-1,3-butadiene with each of the following:(a) 2 mol H2, platinum catalyst(b) 1 mol HCl (product of 1,2-addition)(c) 1 mol HCl (product of 1,4-addition)(d) 1 mol Br2 (product of 1,2-addition)(e) 1 mol Br2 (product of 1,4-addition)(f) 2 mol Br2arrow_forward
- Draw the product formed when each triene undergoes electrocyclic reaction under [1] thermal conditions; [2] photochemical conditions.arrow_forwardReaction of this bicycloalkene with bromine in carbon tetrachloride gives a trans dibro- mide. In both (a) and (b), the bromine atoms are trans to each other. However, only one of these products is formed. CH3 CH3 CH3 Br Br CH,Cl, + Br2 or Br Br (a) (b) Which trans dibromide is formed? How do you account for the fact that it is formed to the exclusion of the other trans dibromide?arrow_forwardDraw the organic product obtained on treatment of each of the following two alkenes with bromine: (a) trans-2-pentene and (b) 1- methylcyclohexene. Having done this, draw the product of the reaction of these same alkenes with bromine in aqueous solution.arrow_forward
- 1.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_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_forwardPara-substituted product was produced when phenol reacts with cyclohexanecarbonyl bromide in the presence of AIB13. -Br Cyclohexanecarbonyl bromide (i) Outline the mechanism for this reaction. (ii) Draw the alternative substituted product formed.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_forwardAlkenes can be converted to alcohols by hydroboration-oxidation. (a) Draw the structure of the alcohol or alcohols formed in the reaction sequence. Clearly indicate stereochemistry by drawing a wedged bond, a dashed bond and two O Hint in-plane bonds per each chiral carbon. Draw hydrogen atoms that are connected to wedge-and-dash bonds.(b) Characterize the product or products of the reactions. The first step of the reaction, hydroboration, involves addition of BH, to the double bond, with -BH, attached to one carbon and hydrogen Be sure to draw hydrogens on oxygen, where applicable. attached to the other. Consider both Rings the regioselectivity and the Select Draw More Erase stereochemistry of this addition. H Diborane, B,H,, is a source of borane, BH,, and can be used 1. B2H6, interchangeably. Diglyme is a solvent. diglyme 2. H2О2, НО", The product or products of the reaction are characterized as being O S. O racemic. O achiral. O R,S (and/or S,R). O R. O S,S. O R.R. O diastereomers.arrow_forward
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