Structure and Physical Properties of Alkynes

Unsaturated hydrocarbons containing carbon–carbon triple bonds are called "alkynes" and are structurally represented as C_nH_2n-2.

Ethyne or acetylene is the simplest alkyne. It is a colorless gas that undergoes combustion at high temperatures and is used for welding.

The alkyne group is of significance as a bioactive moiety in drugs used to treat Parkinson's disease, such as selegiline, and in oral contraceptives like ethynylestradiol.

The carbon–carbon triple bond of acetylene is composed of one σ and two π bonds. The carbon's sp orbitals overlap to create a σ bond, while the 2p_y and 2p_z orbitals' lateral overlap forms two π bonds. The second sp orbital of each carbon participates in a σ bond with the 1s orbital of the hydrogen, generating the carbon–hydrogen bonds.

Thus, alkynes are sp hybridized with a linear geometry and a bond angle of 180°, resulting in the molecules' structural rigidity.

Alkynes show a fifty percent s character given their sp hybridization. As electrons in the s orbital are closer to the nucleus than p orbitals, their energies are lower, and they are more tightly bound to the nucleus. Hence, an increased s character results in stronger and shorter bonds. 

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