CHM 2210C Chapter 4
Key Terms Name: ______
Fill in the blank with the word or
words that best fit the description:
- _____________________:
is the repulsive interaction that occurs when atoms are forced closer
together than their atomic radii allow.
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the strain induced in a molecule when a bond angle deviates from the ideal
tetrahedral value.
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the extra 12 kJ/mol of energy present in the eclipsed conformation of
ethane.
- _____________________:
is the branch of chemistry concerned with the three-dimensional aspects of
molecules.
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the lowest-energy arrangement, is the one in
which the two large methyl groups are as far apart as possible-180 away
from each other.
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chair cyclohexane has six axial hydrogens that
are perpendicular to the ring (parallel to the ring axis).
- _____________________:
all six C-H bonds are as far away from one another as possible, is the
lowest-energy, most stable conformation.
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the six C-H bonds are as close as possible, is the highest-energy, least
stable conformation.
- _____________________:
as bond rotation continues, an energy minimum is reached at the staggered
conformation where the methyl groups are 60 degree apart.
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cyclohexane is not flat; instead, it is puckered
into a three-dimentional conformation that relieves all strain. The C-C-C
angles of cyclohexane can reach the strain-free tetrahedral value if the
ring adopts a _____ conformation. Furthermore, sighting along any one of
the carbon-carbon bonds in a Newman projection shows that _______ cyclohexane has no torsional strain; all neighboring
C-H bonds are staggered.
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the different arrangements of atoms that result from the rotation around
the carbon-carbon single bond.
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learn to draw and access the stability of the substituted cyclohexanes.
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a specific conformation is called a ________.
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the energy difference between axial and equatorial conformers is due to
steric strain caused by so-called ___________.
- _____________________:
six __________ hydrogens that are in the rough
plane of the ring (around the ring equator).
- _____________________:
view the carbon-carbon bond directly end-on and
represent the two carbon atoms by a circle. Bonds attached to the front
carbon are represent by lines going to the center if the circle, and bonds
attached to the rear carbon are represented by lines going to the edge of
the circle.
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When two or more cycloalkane rings are fused together along a common bond
to construct a ___________ molecule.
- _____________________:
Because chair cyclohexane has two kinds of positions, axial and
equatorial, we might expect to find two isomeric forms of a
monosubstituted cyclohexane. In fact, there is only one methylcyclohexane,
one bromo-cyclohexane, and so on, because cyclohexane rings are
conformationally mobile at room temperature. Different chair conformations
readily interconvert, resulting in the exchange of axial and equatorial
positions. This interconversion of chair conformations,
usually referred to as ________.
- _____________________:
view the carbon-carbon bond from an oblique angle and indicate spatial
orientation by showing all C-H bonds
- _____________________:
a second possibility in addition to the chair conformation of cyclohexane,
is also free of angle strain and less stable than chair cyclohexane, having both steric
strain and torsional strain. Carbons 2, 3, 5,
and 6 lie in a plane, with carbons 1 and 4 above
the plane.
- _____________________:
______ cyclohexane is approximately
29 kJ/mol less stable than _____cyclohexane,
although this value is reduced to about 23 kJ/mol by twisting slightly,
thereby relieving some torsinal strain. Even this ________ conformation is
still much more strained than the _______ conformation, though, and
molecules adopt this geometry only under special circumstances.