Organic Chemistry

All the bonds in methane and ethane are sigma bonds because they are all
formed by the end-on overlap of atomic orbitals. All single bondsfound in organic
compounds are sigma bonds.

PROBLEM 15

What orbitals are used to form the 10 covalent bonds in propane

The MO diagram illustrating the overlap of an orbital of one carbon with an
orbital of another carbon (Figure 1.14) is similar to the MO diagram for the end-on
overlap of two porbitals, which should not be surprising since orbitals have 75%
pcharacter.

sp^3

sp^3 sp^3

(CH 3 CH 2 CH 3 )?

(s)

Section 1.8 Bonding in Ethene: A Double Bond 29

σ∗ antibonding molecular orbital

σ bonding molecular orbital

sp^3 atomic

orbital

sp^3 atomic

orbital

Energy

>Figure 1.14

End-on overlap of two orbitals

to form a bonding molecular

orbital and a antibonding

molecular orbital.

s*

s

sp^3

All single bonds found in organic com-

pounds are sigma bonds.

3-D Molecule:

Ethane

1.8 Bonding in Ethene: A Double Bond

Each of the carbon atoms in ethene (also called ethylene) forms four bonds, but each is
bonded to only three atoms:

To bond to three atoms, each carbon hybridizes three atomic orbitals. Because three
orbitals (an sorbital and two of the porbitals) are hybridized, three hybrid orbitals are
obtained. These are called orbitals. After hybridization, each carbon atom has
three degenerate orbitals and one porbital:

To minimize electron repulsion, the three orbitals need to get as far from each
other as possible. Therefore, the axes of the three orbitals lie in a plane, directed
toward the corners of an equilateral triangle with the carbon nucleus at the center. This
means that the bond angles are all close to 120°. Because the sp^2 hybridized carbon

sp^2

ppp

s

sp^2 sp^2

p

sp^2

hybridization

three orbitals are hybridized

hybrid orbitals

sp^2

sp^2

CC

H

ethene

(ethylene)

H

H

H