25.1. Hydrocarbons – The Backbone of Organic Chemistry http://www.ck12.org
FIGURE 25.1
Reaction of ammonium cyanate to form
urea.Bonding and Hybridization in Carbon
Let’s briefly review the basics of covalent bonding as they pertain to carbon. Carbon has four valence electrons,
which have a 2s^2 2p^2 configuration in isolated carbon atoms. These four electrons allow carbon to form four covalent
bonds, which can mean four single bonds or some combination of single, double, and triple bonds.
A carbon atom that has formed single bonds to four different atoms has an sp^3 hybridization. The angles between
these bonds are equal to 109.5°.
FIGURE 25.2
Hybridization of the valence orbitals in a
carbon atom to make a set of four sp^3
orbitals.Recall that a double bond consists of one sigma bond and one pi bond. In order for a double bond to be formed,
each participating carbon atom must have at least one unhybridized p orbital. In a carbon-carbon double bond where
both carbons are bonded to two additional atoms, each carbon is sp^2 hybridized. The double bond includes a sigma
bond between a hybrid orbital from each carbon and a pi bond between the leftover p orbital from each carbon. The
angles between any two bonds for an sp^2 hybridized carbon are approximately 120°.
A triple bond (-C≡C-) requires each of the carbon atoms to be sp hybridized. One hybrid orbital and two p orbitals
from each atom are involved in forming the one sigma and two pi bonds that make up a triple bond. Each carbon