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Copyright © 2017 Pearson Education, Inc.
CHAPTER 4
Isomers: The Arrangement of Atoms in Space
Important Terms
achiral
does not rotate the plane of polarization of plane-polarized light.
amine inversion
a process in which the lone pair of an
sp
3
nitrogen of an amine migrates from one
face of the atom to the other face. This causes the nitrogen’s substituents to move
like an umbrella inverting in a windstorm.
asymmetric center
an atom that is bonded to four different substituents.
chiral
rotates the plane of polarization of plane-polarized light.
chiral probe
something capable of distinguishing between enantiomers.
chromatography
a separation technique in which the mixture to be separated is dissolved in a sol-
vent and the solution is passed through a column packed with an adsorbent station-
ary phase.
cis isomer
the isomer with substituents on the same side of a cyclic structure, or the isomer
with the hydrogens on the same side of a double bond.
cis–trans isomers
isomers that result from not being able to rotate about a carbon–carbon double
(
E
,
Z
isomers)
bond.
configuration
the three-dimensional structure of a chiral compound. The configuration at a spe-
cific atom is designated by
R
or
S
.
configurational isomers
stereoisomers that cannot interconvert unless a covalent bond is broken. Cis–trans
isomers and isomers with asymmetric centers are configurational isomers.
constitutional isomers
molecules that have the same molecular formula but differ in the way the atoms
are connected.
dextrorotatory
the enantiomer that rotates the plane of polarization of plane-polarized light in a
clockwise direction
1
+
2
.
diastereomers
stereoisomers that are not enantiomers.
E
isomer
the isomer with the high-priority groups on opposite sides of the double bond.
enantiomerically pure
only one enantiomer is present in an enantiomerically pure sample.
enantiomeric excess
how much excess of one enantiomer is present in a mixture of a pair of enantiomers,
(optical purity)
expressed as a percentage.
enantiomers
nonsuperimposable mirror-image molecules.