What can a terminal alkyne pka deprotonate

What are the properties of alkynes?

In answering the question "What are the properties of alkynes?" Adequate information on alkynes will also be shown in this article. The alkyne group is a member of the hydrocarbon family. contains a carbon-carbon triple bond in its structure. Alkynes have similar physical properties to Alkanes and Alkenes. Alkynes are more reactive than alkanes and alkynes show reactions similar to alkanes. This article briefly explains the similar properties that alkynes share with the other hydrocarbons and the differences they have. Similar to alkanes and alkenes, alkynes have cyclic members as well as acyclic (noncyclic) members. However, this article will only focus on the acyclic alkynes, which have the general formula of C.nH2n-2.

What are alkynes?

Alkynes are a category of hydrocarbons that contain a carbon-carbon triple bond (C = C). Due to the triple bond, an alkyne has four fewer hydrogen atoms than its Ⓒ. Similar to alkanes and alkenes, alkynes form both cyclic and non-cyclic molecular structures. The general empirical formula for acyclic (noncyclic) alkanes is C.nH2n-2 and that of cyclic alkanes is C.nH2n-4. Some properties of alkynes differ from other hydrocarbons.

General molecular formula of alkynes

Acyclic alkanes have the general molecular formula of CnH2n-2. The smallest alkane is methane (acetylene C2H2). Alkynes with triple bonds at the end of the carbon chain (RC = H) are mentioned terminal alkynes or monosubstituted alkynes. In the group, terminal alkynes are the most acidic hydrocarbon group. Disubstituted alkynes have internal triple bonds (RC = R ').

Chemical properties of alkynes

Molecular structure of alkynes

The carbon-carbon triple bond has the linear geometry. It characterizes the -C = C and C-C = C-C units of the terminal and internal triple bond. The triple bonded carbon atoms are sp-hybridized.

Acidity of Terminal Alkynes

The = C-H bond of the alkynes shows little tendency towards ionization. However, alkanes and alkenes are all weak acids.

Reactivity of alkynes

In contrast to alkanes, alkynes show many reactions with chemical reagents. Most of them are addition reactions like alkenes. Terminal alkynes, however, are also subject to substitution reactions.

In general, both alkanes and alkynes are more reactive than alkanes and alkenes. Alkynes are subject to similar reactions. For example, they go through electrophilic addition reactions with halogens, acids, and oxidizing agents. One of the most significant differences in chemical reactivity between alkenes and alkynes is due to the difference in acidity. Terminal alkynes contain an acidic hydrogen that can be removed by a strong base to yield an acetylide anion. Since the negative charge of the acetylide anion resides in a hybrid orbital with more s-character, making the charge closer to the core, it is more stable than either an alkyl anion or a vinyl anion.

Alkanes and alkenes do not react as follows.

Physical properties of alkynes

Alkynes are similar to alkenes and alkanes in their physical properties. The lower molecular weight molecules are gases at room temperature and as the molecular weight increases, their physical state changes from gas to liquid and then to solids.

Solubility of alkynes

Alkenes and alkynes are relatively polar molecules. Therefore, these two groups are soluble in polar solvents or solvents with low polarity. Alkynes are sparingly soluble in water; that of alkanes is lower than the alkynes.

Alkynes solubility in water > Alkenes solubility in water

Density of alkynes

Alkynes have a low density value like alkanes and alkenes. The densities of alkynes are usually lower than those of water. (Ref: Table 2)

Boiling points of alkynes

In general, alkynes have slightly higher boiling points than the corresponding alkanes and alkenes.


Alkane alkenes alkyne
Butane Butene 1-Butyne 2-Butyne
00C 60C 8.10C 27.0 0C.

Properties of Alkynes - Summary

Alkynes are a group in the hydrocarbon family that has a carbon-carbon triple bond in the structure. Acyclic alkynes have the general chemical formula of C.nH2n-2and that of a cyclic alkyne is CnH2n-4. Acetylene is the smallest member in the alkyne group. Terminal alkynes are the most acidic group in the hydrocarbon family. Alkynes are subject to addition and substitution reactions. Alkynes are more reactive than alkanes.

Alkynes are similar to alkanes and alkynes in terms of their physical properties (boiling point, solubility in water, dipole moment). The solubility of alkynes in water is slightly higher than that of the other hydrocarbons. Their densities are lower than those of water than other hydrocarbons.