22. Select the structure of the major product formed in the following react.onCH
ID: 1089839 • Letter: 2
Question
22. Select the structure of the major product formed in the following react.onCH CH-gi CH2 H2 180 D) CH3CH- CH2 HO 180H ) CH3CH2CH218OH ) CH3CHCH3 180H ) CH3CHCH218OH 180H C) CH3CHCH2OH 80H 3. What would be the major product of the following reaction coned. HBr(xs) ? C6H5CH2OCH3 heat C6H5CH2Br CH3OH A) C6HsBr CH3OH B) C6H5CH2Br +CH3Br C) C6H5CH2H CH3Br 24. Wh ich is the best way to prepare isopropyl methyl ether via the Williamson method? CH3OH(CH2CHOH H2SO4, 140°C ) CH3I+(CH3) 2CHONa CH3I(CH32CHCH2ONa 25. Which is the best method to prepare tert-butyl methyl ether? A) CH3ONa(CH3)3CBr B) CH3ONa (CH3)2CHCH2Br C) CH3OH H2S04i then (CH3) 2C CH2 D) CH30H + CH 3 ) 3CBr E) CH30H (CH3)3COH H2SO4, 140°c 26. Which of the following could be used to synthesize CH3CH2C-CH2? Br H2o OH C) CH3CH2CeCH HBr D) CH3CH2CeCHBr2Explanation / Answer
22. OPTION C. Acid-catalyzed ring-opening reactions of epoxides proceed through the protonation of the epoxide oxygen followed by the attack of the nucleophile in the medium at the site of most stable carbocation giving the final cleaved product. Here, the nucleophile is the 18OH hydroxide ion which attacks the more stable carbocation possible among the two invovled in epoxide ring namely the first and second carbon. Of these, the second carbon is secondary which will have greater hyperconjugation and thus is more stable than the first carbon which is a primary carbon. Thus the first carbon gives the non-radioactive hydroxyl while the second carbon is substituted with the radioactive oxygen since it is the site of nucleophile attack.
23. OPTION D. Nucleophilic attack on ethers involve SN2 mechanistic attack of the nucleophile (bromide ion) on the most stable carbocation thus cleaving the carbon-oxygen bond on the ether and giving proton at the site of highest hinderance and nucleophile at the least hindered site. Here, the nucleophile attacks the benzylic carbon as it is most stable as a carbocation by the extended conjugation from the benzene ring while the least stable carbocation intermediate - the methyl group exits as the stable methoxide ion which is protonated to form methanol and the benzylic carbon becomes benzyl bromide.
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