Interpretation:
The structural formula of the most stable cyclohexadienyl cation intermediate formed in each of the given reactions is to be written. Whether this carbocation is more or less stable than the cyclohexadienyl intermediate formed by benzene, is to be determined.
Concept Introduction:
Compounds containing benzene ring undergo electrophilic
The mechanism of electrophilic aromatic substitution involves two steps.
In the first step, an electrophile accepts an electron pair from pi system of benzene giving an intermediate called as cyclohexadienyl cation or arenium ion intermediate.
In the second step, the cyclohexadienyl cation intermediate undergoes deprotonation to restore the aromaticity of benzene ring.
In order to form cyclohexadienyl cation intermediate, the electrophile must be reactive.
Electron donating substituents present on the benzene ring increase the reactivity towards the electrophilic aromatic substitution reactions by stabilizing the cyclohexadienyl cation intermediate.
When an electron donating substituent is attached to the benzene ring, the cyclohexadienyl cation intermediate formed will be more stable than the cyclohexadienyl intermediate formed by benzene.
When an electron withdrawing substituent is attached to the benzene ring, the cyclohexadienyl cation intermediate formed will be less stable than the cyclohexadienyl intermediate formed by benzene.
Stability of a cyclohexadienyl cation intermediate depends mainly on two factors – its proximity to an electron donating or electron withdrawing group and whether it is an allylic carbocation or not.
Want to see the full answer?
Check out a sample textbook solutionChapter 13 Solutions
ORGANIC CHEMISTRY VOL 2
- The base-promoted rearrangement of an -haloketone to a carboxylic acid, known as the Favorskii rearrangement, is illustrated by the conversion of 2-chlorocyclohexanone to cyclopentanecarboxylic acid. It is proposed that NaOH first converts the a-haloketone to the substituted cyclopropanone shown in brackets and then to the sodium salt of cyclopentanecarboxylic acid. (a) Propose a mechanism for base-promoted conversion of 2-chlorocyclohexanone to the proposed intermediate. (b) Propose a mechanism for base-promoted conversion of the proposed intermediate to sodium cyclopentanecarboxylate.arrow_forwardWittig reactions with the following -chloroethers can be used for the synthesis of aldehydes and ketones. (a) Draw the structure of the triphenylphosphonium salt and Wittig reagent formed from each chloroether. (b) Draw the structural formula of the product formed by treating each Wittig reagent with cyclopentanone. Note that the functional group is an enol ether or, alternatively, a vinyl ether. (c) Draw the structural formula of the product formed on acid-catalyzed hydrolysis of each enol ether from part (b).arrow_forwardEnamines normally react with methyl iodide to give two products: one arising from alkylation at nitrogen and the second arising from alkylation at carbon. For example, Heating the mixture of C-alkylation and N-alkylation products gives only the product from C-alkylation. Propose a mechanism for this isomerization.arrow_forward
- When warmed in dilute sulfuric acid, 1-phenyl-1,2-propanediol undergoes dehydration and rearrangement to give 2-phenylpropanal. (a) Propose a mechanism for this example of a pinacol rearrangement (Section 10.7). (b) Account for the fact that 2-phenylpropanal is formed rather than its constitutional isomer, 1-phenyl-1-propanone.arrow_forward-Ocimene is a pleasant-smelling hydrocarbon found in the leaves of certain herbs. It has the molecular formula C10H16 and a UV absorption maximum at 232 nm. On hydrogenation with a palladium catalyst, 2,6-dimethyloctane is obtained. Ozonolysis of -ocimene, followed by treatment with zinc and acetic acid, produces the following four fragments: (a) How many double bonds does -ocimene have? (b) Is -ocimene conjugated or nonconjugated? (c) Propose a structure for -ocimene. (d) Write the reactions, showing starting material and products.arrow_forwardReaction of -pinene with borane followed by treatment of the resulting trialkylborane with alkaline hydrogen peroxide gives the following alcohol. Of the four possible cis,trans isomers, one is formed in over 85% yield. (a) Draw structural formulas for the four possible cis,trans isomers of the bicyclic alcohol. (b) Which is the structure of the isomer formed in 85% yield? How do you account for its formation? Create a model to help you make this prediction.arrow_forward
- . Write short notes on the following, mentioning reagents, reaction conditions, products formed, mechanism, purification and precautions where necessary• Hydrolysis of 2-bromo-2-methylbutane• Nitration of benzene• Reduction of Nitrobenzene• Ammonolysis of benzoylchloride• Ozonolysis of 2-methylbut-2-enearrow_forwardA reaction flask contains 2-bromopentane in an ethanolic solution of sodium ethoxide at room temperature and result in the formation of two olefnic products. What is responsible for the formation of major and minor products. A. Different activated complex involved in the mechanism. B. Bimolecular nucleophilic substitution reaction. C. Bimolecular elimination reaction D. The presence of sodium ethoxide. E. The hybridization nature of secondary carbocationarrow_forward(ORGANIC CHEMISTRY) (mechanisms) please give a answer for the following mechanism. Provide a detailed stepwise mechanism for the following transformation.arrow_forward
- Two isomers, A and B, of molecular formula C5H8 undergo catalytic hydrogenation with hydrogen gas and palladium on carbon to form the same C5H10 product. On ozonolysis followed by treatment with hydrogen peroxide (H2O2), isomer A gave a product of molecular formula C5H8O4 that has two carboxylic acid groups in it whereas isomer B gave a product of molecular formula C5H8O3 that contains a carboxylic acid group and a ketone group. Which of the following isomeric pairs best match this data?arrow_forwardTwo isomers, A and B, of molecular formula C5H8 undergo catalytic hydrogenation with hydrogen gas and palladium on carbon to form the same C5H10 product. On ozonolysis followed by treatment with hydrogen peroxide (H2O2), isomer A gave a product of molecular formula C5H8O4 that has two carboxylic acid groups in it whereas isomer B gave a product of molecular formula C5H8O3 that contains a carboxylic acid group and a ketone group. What is the isometric pair of A and B that corresponds?arrow_forwardBenzenediazonium carboxylate decomposes when heated to yield N2, CO2, and a reactive substance that can't be isolated. When benzenediazonium carboxylate is heated in the presence of furan, the following reaction is observe. Propose a structure for the intermediate in this reaction.arrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning