Interpretation:
The products in the given cope rearrangements has to be predicted with stereochemistry.
Concept Introduction:
Cope-rearrangement:
It is a pericyclic reaction that involves the redistribution of six electrons through the formation of a cyclic transition state from which a
Example with mechanism of cope-arrangement:
In this mechanism, two pi-bonds and one sigma bond of the reactant molecule has been rearranged and formed two new pi-bonds through a cyclic transition state.
Identification of cope-rearrangement in a
In the cope-rearrangement, the flow of electrons takes place between six bonds that are bonded as
The carbon atoms that are involving in the cope-rearrangement are shown in bold.
Stereochemistry in a product formed:
- • In the product of a
chemical reaction , if a carbon atom has been attached with four different carbon atoms, then it is known as chiral carbon atom or stereocenter in the product. - • The bonds of the
functional groups because of which a new chiral carbon is supposed to form have to be represented in solid wedge bond and hashed-wedge bonds according to the particular enantiomer. - • Racemic mixture is the mixture of two enantiomers in equal proportions.
- • Enantiomers are non-superimposable mirror images.
- • Achiral product is the product in which there won’t be any chiral centre or stereocenter.
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Chapter 20 Solutions
Organic Chemistry
- Show how the following starting material is converted to the given product by a series of two pericyclic reactions. Account for the observed stereochemistry.arrow_forwardIdentify the following pericyclic reaction; explain the course, product distribution and stereochemistry of the reaction. Where the first product is produced 70% and the second product is produced 30%.arrow_forwardPredict the products of the following reactions. Show stereochemistry and regiochemistry of the product, where relevant.arrow_forward
- 5b. Enolates have two resonance structures, and can react on oxygen instead of carbon. Show the product of reaction in the oxygen, and then show how it can be converted to the product with the allyl group on carbon.arrow_forwardPredict the major product of the following reactions. Indicate stereochemistry when relevant.arrow_forwardPredict the products of the following reactions, showing stereochemistry where appropriate.arrow_forward
- Predict the products for each of the following reactions and propose a mechanism that explains the formation of each product.arrow_forwardPredict the products and show the mechanisms for the following reactions. Please indicate the correct stereochemistry where necessary.arrow_forwardBr Brz CH3 CH3 H3C CH2CI2 H3C Br Electrophilic addition of bromine, Br2; to alkenes yields a 1,2-dibromoalkane. The reaction proceeds through a cyclic intermediate known as a bromonium ion. The reaction occurs in an anhydrous solvent such as CH,Cl). In the second step of the reaction, bromide is the nucleophile and attacks at one of the carbons of the bromonium ion to yield the product. Due to steric clashes, the bromide ion always attacks the carbon from the opposite face of the bromonium ion so that a product with anti stereochemistry is formed. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions Br: :Br: .CH3 H3C H3C CH3 Br:arrow_forward
- Which products are obtained by the following reactions (a) and (b)? Specify the expected main product, if several products can be formed.arrow_forwardAldehydes and ketones react with thiols to yield thioacetals just as they react with alcohols to yield acetals. Predict the product of the following reaction, and propose a mechanism:arrow_forwardAlkyl halides undergo nucleophilic substitution and elimination reactions. When the kinetics of the reaction are measured, if the rate of the reaction is found to be dependent only upon the concentration of the alkyl halide the reaction is first order. The substitution reaction is thus termed SN1, and the elimination reaction is termed E1. These reactions are unimolecular and occur in two steps. The first step is rate-limiting and involves the loss of the leaving group to form a carbocation. In the second, fast, step the nucleophile adds to the carbocation in the SN1 reaction or elimination occurs to give an alkene in the E1 reaction. Because the carbocation is planar, the nucleophile can add to either face and therefore racemization is usually observed although solvent effects can influence this somewhat. E1 elimination follows Zaitsev’s rule and typically yields the most substituted alkene as the major product. Conditions which favor the SN1/E1 pathway include the use of a weak…arrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning