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974 CHAPTER 23 
 
dictates that styrene (which has eight carbon atoms) must 
be the only source of carbon atoms. Therefore, we must 
create the following bond, indicated with a wavy line: 
 
 
 
Next, draw the two organohalides that are necessary for 
the coupling process. In this case, we need two identical 
alkyl halides, as shown: 
 
 
 
These alkyl halides can be made from styrene via the 
anti-Markovnikov addition of HBr (see Section 11.10): 
 
 
 
The entire synthesis is shown below: 
 
 
23.10. 
(a) Upon treatment with CH2I2 and Zn-Cu, an alkene will 
undergo a Simmons-Smith reaction, thereby converting 
the C=C unit into a cyclopropane ring (with introduction 
of a methylene group): 
 
 
 
In this case, the product has no chiral centers, so wedges 
and dashes are not drawn. 
 
(b) Upon treatment with CH2I2 and Zn-Cu, an alkene 
will undergo a Simmons-Smith reaction, thereby 
converting the C=C unit into a cyclopropane ring (with 
introduction of a methylene group): 
 
 
 
In this case, the product has two chiral centers, and is a 
meso compound (it does not have an enantiomer). 
Introduction of the methylene group can occur on either 
face of the  bond, giving the same meso compound in 
either case: 
 
 
(c) Upon treatment with CH2I2 and Zn-Cu, an alkene will 
undergo a Simmons-Smith reaction, thereby converting 
the C=C unit into a cyclopropane ring (with introduction 
of a methylene group): 
 
 
In this case, the product has two chiral centers, and is a 
meso compound (it does not have an enantiomer). 
Introduction of the methylene group can occur on either 
face of the  bond, giving the same meso compound in 
either case: 
 
 
(d) Upon treatment with CH2I2 and Zn-Cu, an alkene 
will undergo a Simmons-Smith reaction, thereby 
converting the C=C unit into a cyclopropane ring (with 
introduction of a methylene group): 
 
 
 
In this case, the product is not a meso compound. Since 
the methylene group can be installed on either face of the 
 bond, we expect a pair of enantiomers. 
 
(e) Upon treatment with CH2I2 and Zn-Cu, an alkene will 
undergo a Simmons-Smith reaction, thereby converting 
the C=C unit into a cyclopropane ring (with introduction 
of a methylene group). In this case, the starting alkene 
has a trans configuration, which is preserved in the 
product. Introduction of the methylene group can occur 
on either face of the  bond, giving rise to a pair of 
enantiomers: 
 
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