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Why is the C≡C bond distance of acetylene shorter than the C=C bond distance? The molecular secret that will surprise you!
Acetylene, with the chemical formula C2H2, is the simplest alkyne and a hydrocarbon molecule with a triple bond. Compared with the well-known double-bond olefins (such as ethylene, C2H4), the C≡C bond distance of acetylene is more compact, even tighter than that of C=C The key pitch is even shorter. This phenomenon not only reflects the structure and stability of atoms in molecules, but also has a close relationship with their bonding properties and electron distribution.
Structural differences between double bonds and triple bonds
In the acetylene molecule, the C≡C bond length is about 118 picometers, while the C=C bond length in ethylene is 132 picometers.
Why is there such a difference? The key lies in the mix of carbon atoms and the nature of the bonds they form. The carbon atoms of acetylene are sp hybridized, which means that each carbon atom has two unhybridized p orbitals to form two π bonds and one sp orbital to form a σ bond. This structure makes the formation of a triple bond very difficult. The structure is stronger than double bonds. As we all know, the stronger the chemical bond, the shorter the distance is usually.
Strength and its influencing factors
The bond energy of a triple bond is 839 kJ/mol, while the bond energy of a double bond is approximately 610 kJ/mol.
In addition to the bond distance, the strength of these bonds is also a factor we need to consider. For the C≡C bond of acetylene, the attraction between carbon atoms is further enhanced through the formation of the triple bond, making this bond not easily broken. So even though the triple bond may not seem very large from a distance, the overall stability is evident due to this strength.
Specificities of the hydrogenation process
In chemical reactions, acetylene, as a "more unsaturated" molecule, reacts selectively with hydrogen. During partial hydrogenation, acetylene can absorb two hydrogen molecules and eventually turn into ethylene. However, if a suitable catalyst is used, it may stop at the ethylene stage. This is because under different catalysts and reaction conditions, the hydrogenation process The selectivity will change.
ConclusionIf we compare the properties of double bonds and triple bonds, we can easily find that the reactivity and stability of these structures in chemical reactions are completely different. The mystery here makes us wonder whether future chemical research will bring us a deeper understanding of molecular structure and properties?
