Section 5.4 Isomers with One Asymmetric Carbon 185Tutorial:
Identification of asymmetric
carbon atomsNotice that the only carbons that can be asymmetric carbons are hybridized car-
bons; and sphybridized carbons cannot be asymmetric carbons because they can-
not have four groups attached to them.
An asymmetric carbon is also known as a chirality center. We will see that
atoms other than carbon, such as nitrogen and phosphorus, can be chirality
centers—when they are bonded to four different atoms or groups (Section 5.17). In
other words, an asymmetric carbon is just one kind of chirality center. A chirality
center also belongs to a broader group known as stereocenters. Stereocenters will be
defined in Section 5.5.
PROBLEM 4Which of the following compounds have asymmetric carbons?a. d.b. e.c. f.PROBLEM 5 SOLVEDTetracycline is called a broad-spectrum antibiotic because it is active against a wide variety
of bacteria. How many asymmetric carbons does tetracycline have?SOLUTION First, locate all the hybridized carbons in tetracycline. (They are num-
bered in red.) Only hybridized carbons can be asymmetric carbons, because an asym-
metric carbon must have four different groups attached to it. Tetracycline has nine
hybridized carbons. Four of them (#1, #2, #5, and #8) are not asymmetric carbons because
they are not bonded to four different groups. Tetracycline, therefore, has five asymmetric
carbons.5.4 Isomers with One Asymmetric Carbon
A compound with one asymmetric carbon, such as 2-bromobutane, can exist as two
different stereoisomers. The two isomers are analogous to a left and a right hand.
Imagine a mirror between the two isomers; notice how they are mirror images of each
other. The two stereoisomers are nonsuperimposable mirror images—they are differ-
ent molecules.
H 3 C HH 3 C CH 3
OH Ntetracycline1 26 8 3547 9OHO O OOH
OH OHCNH 2sp^3sp^3sp^3CHCHCH 3NH 2CH 3 CH 2 CCH 2 CH 2 CH 3 CH 2BrCH 3CH 3 CH 2 CHCH 2 CH 3BrCH 3 CH 2 CHCH 3CH 3CH 3 CH 2 CHCH 3 CH 3 CH 2 OHClsp^2sp^3