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208          CHAPTER 7           
 
The better retrosynthesis is based on disconnection of 
bond b, because it involves both a good electrophile and 
a good nucleophile: 
 
 
 
The SN2 process portrayed in retrosynthesis b is 
favorable, because it involves a strong nucleophile and a 
primary substrate, so this reaction is expected to give the 
desired target molecule. 
 
 
 
 
7.47. 
(a) The parent is the longest chain, which is three carbon 
atoms in this case (propane). There is only one 
substituent (chloro), and its locant is assigned as 2 (as 
shown below), so the systematic name for this compound 
is 2-chloropropane. The common name is isopropyl 
chloride. 
 
 
(b) The parent is the longest chain, which is three carbon 
atoms in this case (propane). There are two substituents 
(bromo and methyl), and their locants are assigned as 2 
and 2, as shown below. Substituents are alphabetized in 
the name (bromo precedes methyl), so the systematic 
name is 2-bromo-2-methylpropane. The common name 
is tert-butyl bromide. 
 
 
(c) The parent is the longest chain, which is three carbon 
atoms in this case (propane). There is only one 
substituent (iodo), and its locant is assigned as 1 (as 
shown), so the systematic name for this compound is 1-
iodopropane. The common name is propyl iodide. 
 
 
 
(d) The parent is the longest chain, which is four carbon 
atoms in this case (butane). There is only one substituent 
(bromo), and its locant is assigned as 2 (as shown 
below). The compound has a chiral center, so the 
configuration must be indicated at the beginning of the 
name: (R)-2-bromobutane. The common name is (R)-
sec-butyl bromide. 
 
 
(e) The parent is the longest chain, which is three carbon 
atoms in this case (propane). There are three substituents 
(chloro, methyl, and methyl), and their locants are 
assigned as 1, 2, and 2, respectively, as shown below. 
Substituents are alphabetized in the name (chloro 
precedes methyl). Make sure that each methyl group 
receives a locant (2,2-dimethyl rather than 2-dimethyl). 
The systematic name is therefore 1-chloro-2,2-
dimethylpropane. The common name is neopentyl 
chloride. 
 
 
7.48. 
(a) We begin by identifying the parent. The longest 
chain is seven carbon atoms, so the parent is heptene. 
There are four substituents (highlighted), all of which are 
methyl groups. Notice that the parent chain is numbered 
starting from the side that is closest to the  bond. 
According to this numbering scheme, the methyl groups 
are located at C3, C4, C5 and C5. Finally, we use the 
prefix “tetra” to indicate the presence of four methyl 
groups, and we include a locant that identifies the 
position of the double bond (“3” indicates that the double 
bond is located between C3 and C4): 
 
 
 
(b) The parent is a six-membered ring (cyclohexene). 
There is only substituent (located at C1: 
 
 
 
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