Shapes Of Simple Organic Compounds

Methane molecule

A molecule of methane contains four C-C , σ bonds.

Orbital picture of methane

Bond length and bond angles 

Ethane Molecule

It contains 6 C-H σ bonds and one C-C σ bond.

Orbital picture of ethane

Bond lengths and bond angle in ethane

Ethene molecule

The carbon-carbon double bond of ethene consists of a strong carbon-carbon σ- bond and a weak carbon-carbon π bond.

Ethyne molecule

The carbon-carbon triple bond of ethyne consists of a strong carbon-carbon σ- bond and two weak carbon-carbon π bond.

Characteristic Features of π-bonds

For π-bond formation, it is essential that the p-orbital on the adjacent carbon atoms must be parallel for a proper sideways overlap.

1) All  the atoms directly attached to the carbon atoms of the double bond lie in the same plane.

2) The p-orbital of a π-bond are mutually parallel and are perpendicular to the plane of the molecule.

3) Rotation of one CH₂ fragment w.r.t the other interferes with the maximum overlaps of the p-orbitals.Therefore , such a rotation about carbon-carbon double bond is restricted.

4) The electron charge cloud of the π-bond lies above and below  the plane of the bonding atoms.This allows the π-electrons being easily available to the attacking reagents.