Question:
Acetylenic hydrogens are acidic because
Acetylenic hydrogens are acidic because
Updated On: Jun 9, 2024
- sigma electron density of C-H bond in acetylene is nearer to carbon which has 50% s-character
- acetylene has only one hydrogen on each carbon
- acetylene contains least number of hydrogens among the possible hydrocarbons having two carbons
- acetylene belong to the class of alkynes with molecular formula $C_nH_{2n-n}$
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The Correct Option is A
Solution and Explanation
Acidic character of alkynes can be explained on the basis of sp-hybridisation state of the carbon atom in alkynes. We know that an electron in
s orbital is more tightly held than in a p orbital because s-electrons are more closer to the nucleus. In sp-hybridisation, s-character is more $(50 \%)$ as
compared to $sp^2-(33 \%)$ or $sp^3-(25 \%)$ hybrid orbitals. Due to very large s-character, the electrons in sp-hybrid orbitals are held tightly by the nucleus and are quite electronegative. Consequently, the electron pair of $H-C \equiv$ bond gets displaced more towards the carbon atom and help in the release of $H^+$ ions. For a examples ethyne react with sodium metal and release the $H^+$ ions. $\hspace15mm CH \equiv CH +Na \longrightarrow HC \equiv C^- Na^+ $
s orbital is more tightly held than in a p orbital because s-electrons are more closer to the nucleus. In sp-hybridisation, s-character is more $(50 \%)$ as
compared to $sp^2-(33 \%)$ or $sp^3-(25 \%)$ hybrid orbitals. Due to very large s-character, the electrons in sp-hybrid orbitals are held tightly by the nucleus and are quite electronegative. Consequently, the electron pair of $H-C \equiv$ bond gets displaced more towards the carbon atom and help in the release of $H^+$ ions. For a examples ethyne react with sodium metal and release the $H^+$ ions. $\hspace15mm CH \equiv CH +Na \longrightarrow HC \equiv C^- Na^+ $
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Concepts Used:
Hydrocarbons
Hydrocarbons can be described as organic compounds that consists only hydrogen and carbon atoms. These compounds are of different types and thereby have distinct natures. Hydrocarbons are colorless gases and are known for discharging faint odours. These have been categorized under four major classes named as alkynes, alkanes, alkenes, and aromatic hydrocarbons.
Types of Hydrocarbons
- Saturated hydrocarbons - Saturated hydrocarbons are those compounds where there is a single bond exists between carbon atoms and are saturated with atoms of hydrogen.
- Unsaturated hydrocarbons - Hydrocarbons comprises of at least one double or triple bond between carbon atoms are known as unsaturated hydrocarbons.
- Aliphatic hydrocarbons - The term denotes the hydrocarbons formed as an outcome of the chemical degradation of fats. Aliphatic hydrocarbons are basically chemical compounds.
- Aromatic hydrocarbons - They are distinguished because of the presence of benzene rings in them. They give away distinct types of aroma. These hydrocarbons comprises of only hydrogen and carbon atoms.