Alkynes – the structure of triple bond (ethyne)
Ethyne is the simplest molecule of the alkyne series. In this case, each carbon atom is sp hybridized forming two sp hybrid orbitals. These two sp hybrid orbitals lie along the straight line and the bond angle between them is 180◦. The two unhybridized p orbitals are perpendicular to each other and also to the axis of the hybridized orbitals.
In the triple bond formation, on sp hybridized orbital of one carbon atom overlaps axially with the similar sp hybrid orbital of the other carbon atom to form a sigma bond. Each of the two unhybridized orbitals of one carbon overlaps sidewise with a similar orbital of the other carbon atom to form two weak π-bonds. The remaining sp hybrid orbital of each carbon atom overlaps with 1s orbital of hydrogen to form C-H bond. The structure of the triple bond is being illustrated by the orbital structure of ethyne as shown in the figure below: