http://www.ck12.org Chapter 25. Organic Chemistry
FIGURE 25.8
Cyclopropane is the simplest cycloalkane.
Its highly strained geometry makes it
rather unstable and highly reactive.The carbon atoms in cycloalkanes are stillsp^3 hybridized, with an ideal bond angle of 109.5°. However, due to the
triangular structure of cyclopropane, the sum of the three C-C-C bond angles must be 180°, which means that each
bond angle is 60°. This major deviation from the ideal angle is called ring strain, and it makes cyclopropane a fairly
unstable and reactive molecule. Ring strain is decreased for cyclobutane, which has bond angles of 90°, but it is still
significant. In contrast, cyclopentane has bond angles of about 108°. This minimal ring strain makes cyclopentane a
much more stable compound.
Cyclohexane is a six-carbon cycloalkane (Figure25.9).
FIGURE 25.9
Cyclohexane is one of the most stable
cycloalkanes.All three of these depictions of cyclohexane are somewhat misleading because the molecule is not planar. For
a planar hexagon, the internal bond angles would each be 120°. In order to reduce the ring strain and attain a
bond angle of approximately 109.5°, the molecule is puckered. The puckering of the ring means that every other