Answer to Question #152328 in Organic Chemistry for Jazmyne Vera

Question

Contrast orbital hybridization in the first carbon of ethane with orbital hybridization in the first carbon of ethene, and describe specifically the different hybridizations and how they affect the geometry of each molecule.

Answer 1

The ground state configuration of C-atom is 1s² 2s² 2p².

During ethane (C₂H₆) formation, one s orbital and p_x, p_y, and p_z orbitals of C-atom undergo sp³ hybridization. As a result four sp³ hybridized orbitals are formed for each the carbon atoms of ethane molecule.

Now this newly formed molecular hybrid orbitals form different bonds between the electrons of C and H. One of the four sp³ hybrid orbitals of one carbon atom will overlap with 1 s-orbital of the hydrogen atom to produce 3 sigma bonds. Additionally the last remaining sp³ hybrid orbital will overlap with one sp³ orbital of another carbon atom and form a sigma bond between two C-atoms.

The geometry around one carbon atom of ethane is tetrahedral molecular geometry with 109.28⁰ bond angles

 

During ethene (C₂H₄) formation, carbon atom gets excited and the configuration is represented as

                           

Here one s orbital and two p orbitals of C-atom undergo sp² hybridization forming a total of three sp² orbitals.The third 2p orbital remains unhybridised. In ethene the two carbon atoms form a σ bond by overlapping one sp² orbital from each carbon atom. The π bond between the carbon atoms perpendicular to the molecular plane is formed by unhybridized 2p_z–2p_z overlap. Each carbon atom forms covalent C–H bonds with two hydrogens by s (of hydrogen)–sp² (of carbon) overlap.

The geometry around one carbon atom of ethane is trigonal planar molecular geometry with 120° bond angles