Problem 57
Question
Which of the following shows acidic character? (a) \(\mathrm{CH}_{3}-\mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH}\) (c) \(\mathrm{CH}_{2}=\mathrm{CH}_{2}\) (d) \(\mathrm{CH}_{3} \equiv \mathrm{C}-\mathrm{CH}_{3}\)
Step-by-Step Solution
Verified Answer
(b) \( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \) shows acidic character.
1Step 1: Identify the Compounds
The given options represent different organic compounds: (a) \( \mathrm{CH}_{3}-\mathrm{CH}_{3} \) is ethane, an alkane. (b) \( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \) is propyne, an alkyne. (c) \( \mathrm{CH}_{2}=\mathrm{CH}_{2} \) is ethene, an alkene. (d) \( \mathrm{CH}_{3} \equiv \mathrm{C}-\mathrm{CH}_{3} \) is 2-butyne, another alkyne.
2Step 2: Understand Acidic Character in Hydrocarbons
The acidic character in hydrocarbons is typically due to the presence of a hydrogen atom connected to an sp hybridized carbon, as in alkynes, which can release \( H^+ \) ions. Alkanes and alkenes, with sp3 and sp2 hybridization respectively, usually do not show acidic properties.
3Step 3: Analyze the Compounds for Acidity
(a) Ethane (\( \mathrm{CH}_{3}-\mathrm{CH}_{3} \)) has only sp3 hybridized carbons and no acidic hydrogen. (b) Propyne (\( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \)) has an acetylenic hydrogen attached to an sp hybridized carbon, making it slightly acidic. (c) Ethene (\( \mathrm{CH}_{2}=\mathrm{CH}_{2} \)) has sp2 hybridized carbons, with no acidic hydrogen. (d) 2-Butyne (\( \mathrm{CH}_{3} \equiv \mathrm{C}-\mathrm{CH}_{3} \)) has no hydrogen connected to sp hybridized carbon capable of showing acidity.
4Step 4: Determine the Acidic Compound
From the analysis, propyne (\( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \)) in option (b) shows acidic character because of the acetylenic hydrogen attached to an sp hybridized carbon.
Key Concepts
sp hybridized carbonhydrocarbon acidityalkynes
sp hybridized carbon
Carbon atoms can form various types of bonds, resulting in different hybridization states. When a carbon atom is involved in triple bonds, it undergoes sp hybridization. This involves the mixing of one s orbital and one p orbital to form two equivalent sp orbitals, leaving two other p orbitals unhybridized.
This hybridization results in a linear structure, which is typical for alkynes. The strong 3 bond formed is shorter and stronger, contributing to the unique properties of sp hybridized carbons.
In summary, sp hybridization results in two essential characteristics:
This hybridization results in a linear structure, which is typical for alkynes. The strong 3 bond formed is shorter and stronger, contributing to the unique properties of sp hybridized carbons.
In summary, sp hybridization results in two essential characteristics:
- Linear geometry.
- Involvement in a triple bond, as seen in alkynes.
hydrocarbon acidity
The acidity of hydrocarbons depends significantly on the type of bonding and hybridization of the carbon atoms involved. When a hydrogen atom is attached to an sp hybridized carbon, as in alkynes, it displays a higher propensity to release a proton. This makes such hydrogen atoms slightly more acidic compared to those bonded to sp2 or sp3 hybridized carbons.
The primary reason for this increased acidity is the s-character of the bond. In an sp hybridized carbon, 50% of the orbital's character is s, compared to 33% in sp2 and 25% in sp3, leading to greater electronegativity and propensity to hold electrons closely.
This characteristic makes alkynes unique among hydrocarbons in terms of acidity. Consequently, propyne (\( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \)), with a terminal acetylenic hydrogen, displays acidic properties, albeit weak compared to traditional acids.
The primary reason for this increased acidity is the s-character of the bond. In an sp hybridized carbon, 50% of the orbital's character is s, compared to 33% in sp2 and 25% in sp3, leading to greater electronegativity and propensity to hold electrons closely.
This characteristic makes alkynes unique among hydrocarbons in terms of acidity. Consequently, propyne (\( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \)), with a terminal acetylenic hydrogen, displays acidic properties, albeit weak compared to traditional acids.
alkynes
Alkynes are a class of hydrocarbons that contain at least one carbon-carbon triple bond, making them distinctive due to their linear structure and sp hybridization. This unique bonding arrangement imparts specific properties to alkynes, particularly acidity.
An excellent example of an alkyne is propyne (\( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \)). Alkynes in general can undergo reactions typical for both unsaturated and slightly acidic compounds.
Alkynes have the ability to:
An excellent example of an alkyne is propyne (\( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{CH} \)). Alkynes in general can undergo reactions typical for both unsaturated and slightly acidic compounds.
Alkynes have the ability to:
- Participate in addition reactions, breaking the triple bond to form new compounds.
- Release protons under specific conditions due to the presence of acetylenic hydrogens connected to sp hybridized carbons.
Other exercises in this chapter
Problem 55
There is free rotation about the carbon-carbon \(\sigma\)-bond in ethane. This means that the energy difference between the staggered and eclipsed conformers is
View solution Problem 56
Potassium salt of 2,3 -dimethyl maleic acid on electrolysis gives (a) ethyene (b) propyne (c) 2-butyne (d) 1 -butyne
View solution Problem 58
Which among the following alkyne will give an aldehyde on hydroboration oxidation reaction? (a) \(\mathrm{CH} \equiv \mathrm{CH}\) (b) \(\mathrm{CH}_{3}-\mathrm
View solution Problem 59
Which of the reagents on reaction with cyclohexanol gives best yield of cyclohexene? (a) conc. \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (b) conc. \(\mathrm{HCl}\) (c)
View solution