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The H–C≡C–H bond angles in acetylene are exactly 180°. Alkynes have a rod-like shape as a result of the bond angle. Cyclic alkynes, on the other hand, are extremely uncommon. It is impossible to separate benzyne. 121 picometers is a much shorter distance than the C=C distance in alkenes (134 pm) or the C–C bond distance in alkanes (140 pm) for the C–C bond (153 pm).
The triple bond has a bond strength of 839 kJ/mol, which indicates that it is quite strong. The sigma bond contributes 369 kJ/mol of bond strength, the first pi bond contributes 268 kJ/mol, and the second pi-bond gives 202 kJ/mol of bond strength, with the sigma bond contributing the most. When we talk about bonding, we normally think about it in terms of molecular orbital theory, which acknowledges that triple bonds are formed when two orbitals of the same atom overlap. The carbon atoms in an alkyne bond are sp hybridised, which means that they each contain two unhybridised p orbitals and two sp hybrid orbitals, according to the terminology of valence bond theory. The overlap of a sp orbital from each atom results in the formation of a single sp–sp sigma bond. Three bonds are formed when the p orbitals of two atoms overlap and generate two pi bonds, for a total of three bonds between the atoms. It is possible for each atom’s remaining sp orbital to create a sigma bond with another atom, for example, with the hydrogen atoms in the parent acetylene. The two sp orbitals of the carbon atom are positioned on opposing sides of the atom.
Terminal Alkynes
A terminal alkyne is an alkyne in whose molecule there is at least one hydrogen atom bonded to a triply bonded carbon atom. eg:
Internal Alkynes
An internal alkyne is an alkyne in whose molecule there are no hydrogen atoms bonded to triply bonded carbon atoms.
eg: 
Difference Between Terminal and internal alkynes
Internal alkynes have carbon substituents on each acetylenic carbon, whereas external alkynes do not. Diphenylacetylene and 3-hexyne are two examples of symmetrical compounds.
Terminal alkynes are represented by the formula RC2H. Methylacetylene is one example of this (propyne using IUPAC nomenclature). Terminal alkynes, such as acetylene itself, are slightly acidic, having pKa values in the range of 25 to 30. They are significantly more acidic than alkenes and alkanes, which have pKa values in the range of 40 and 50, respectively, indicating that they are more basic. Terminal alkynes can have their acidic hydrogen substituted by a variety of groups, resulting in the formation of halo-, silyl-, and alkoxy alkanes. It is known as acetylides to refer to the carbanions formed by deprotonation of terminal alkynes.
Conclusion
The H–C≡C bond angles in the compound acetylene are 180°. Alkynes have a rod-like shape due to this bond angle. Cyclic alkynes, on the other hand, are uncommon. Benzyne is a very volatile compound. The C–C bond in alkanes is shorter than the C=C bond in alkenes (134 pm), and the C–C bond in alkanes is shorter than the C=C bond in alkenes (134 pm) (153 pm).Alkynes have physical characteristics that are identical to those of their parent alkane or alkene. They are insoluble in water and polar solvents because they are nonpolar compounds with a lower density than water. They do, however, dissolve well in nonpolar organic solvents. At normal temperature, lower-molecular-weight alkynes like ethyne and propyne exist as gases, but higher-molecular-weight alkynes like 1-octyne and 1-decyne exist as liquids.
