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General Chemistry Principles, Patterns, and Applications, 2011

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Determine whether the compound is chiral. In most cases, this means that at least one carbon is bonded<br />

to four different groups. If the compound is chiral, it exists as enantiomers.<br />

Solution:<br />

a. The carbons in –CH 3 <strong>and</strong> –CH 2– are each bound to more than one hydrogen, so they<br />

are achiral. The central carbon is bound to two identical ethyl groups, so it is also achiral.<br />

Because there are no chiral centers in this compound, it has no enantiomers.<br />

b. All carbons are bonded to at least two H atoms except for the one bonded to Br, which is<br />

bonded to four different groups: –Br, –CH 3, –H, <strong>and</strong> –CH 2CH 3. The compound therefore<br />

has one chiral center <strong>and</strong>, as a result, exists as enantiomers: the structure shown <strong>and</strong> its<br />

nonsuperimposable mirror image.<br />

c. The carbons in each –CH 3 are bonded to more than one hydrogen, so they are achiral.<br />

One carbon is bonded to two –CH 3 groups, making it achiral also. This compound has no<br />

enantiomers.<br />

d. One carbon is bonded to three hydrogens <strong>and</strong> one to two oxygens, so they are achiral.<br />

The central carbon is bonded to four different groups: –CH 3, –H, –NH 2, <strong>and</strong> –CO 2H, so it is<br />

chiral, <strong>and</strong> the compound has two enantiomers.<br />

Exercise<br />

Which of these compounds have at least one pair of enantiomers?<br />

Answer:<br />

(c)<br />

Optical Activity of Enantiomers<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

2221

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