Alkenes contain a double carbon-carbon bond that results in trigonal planar molecular geometry around the C=C bond. The double bond restricts rotation due to overlapping pi orbitals, unlike single bonds that allow free rotation. This lack of rotation makes portions of alkene molecules flat and two-dimensional rather than three-dimensional like alkanes with single bonds.
2. • An alkene is an unsaturated hydrocarbon
containing a double carbon-carbon bond.
• The molecular shape around the C=C
double bonds in an alkene and the H-C-H
bond angle in ethene is trigonal planar 120.
• Because of the overlapping by the orbitals
responsible for the sigma and pi binds in
the C=C bond overlap, they don’t’ rotate.
3. The C=C double bonds don’t rotate freely
like the C-C bonds do because when a
carbon has a double bond, the molecules
are bonded twice, which creates pi bonding
and makes the molecules move less.
4. Because of the overlapping by the orbitals
responsible for the sigma and pi binds in
the C=C bond overlap, they don’t’ rotate.
5. A portion of the
molecule is flat and only
2-dimensional.
Alkenes - 3 atoms and 1
double bond
Carbons #1 and 2 both have only 3
other atoms attached and one
double bond, therefore both are
centers of trigonal planar geometry.
Carbon # 3 has 4 other atoms
attached and all single bonds,
therefore it is the center of a
tetrahedron.
6. • When a carbon has a double bond
it can’t move around like it can
when it has a single bond. The
double bond holds it together
tighter like in alkenes.
