Dolbier HW Solutions 275

Dolbier HW Solutions 275 - c The conversion of styrene to...

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The E isomer is formed from either the 1 R ,2 S or the 1 S ,2 R chloride (or from a racemic mixture of the two). 11.37 ( a ) The conversion of ethylbenzene to 1-phenylethyl bromide is a benzylic bromination. It can be achieved by using either bromine or N -bromosuccinimide (NBS). ( b ) The conversion of 1-phenylethyl bromide to 1,2-dibromo-1-phenylethane cannot be achieved cleanly in a single step. We must reason backward from the target mole- cule, that is, determine how to make 1,2-dibromo-1-phenylethane in one step from any start- ing material. Vicinal dibromides are customarily prepared by addition of bromine to alkenes. This suggests that 1,2-dibromo-1-phenylethane can be prepared by the reaction The necessary alkene, styrene, is available by dehydrohalogenation of the given starting material, 1-phenylethyl bromide. Thus, by reasoning backward from the target molecule, the synthetic scheme becomes apparent.
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Unformatted text preview: ( c ) The conversion of styrene to phenylacetylene cannot be carried out in a single step. As was pointed out in Chapter 9, however, a standard sequence for converting terminal alkenes CH 2 C 6 H 5 CH C 6 H 5 CHCH 3 Styrene 1,2-Dibromo-1-phenylethane 1-Phenylethyl bromide Br NaOCH 2 CH 3 CH 3 CH 2 OH Br 2 C 6 H 5 CHCH 2 Br Br CH 2 C 6 H 5 CH C 6 H 5 CHCH 3 Styrene 1-Phenylethyl bromide Br NaOCH 2 CH 3 CH 3 CH 2 OH CH 2 C 6 H 5 CHCH 2 Br C 6 H 5 CH 1,2-Dibromo-1-phenylethane Styrene Br 2 1 Br C 6 H 5 CHCH 3 Br C 6 H 5 CHCH 2 Br Br Br 2 , light or NBS, heat C 6 H 5 CHCH 3 Br 1-Phenylethyl bromide C 6 H 5 CH 2 CH 3 Ethylbenzene H H C 6 H 5 C 6 H 5 CH 3 Cl R S (1 R ,2 S )-1-Chloro-1,2-diphenylpropane H CH 3 C 6 H 5 C 6 H 5 ( E )-1,2-Diphenylpropene (87%) NaOCH 2 CH 3 ARENES AND AROMATICITY 269...
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This note was uploaded on 09/26/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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