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Preparation of Alkanes NEET MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 25, 2023 25:24 PM | #NEET
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Preparation of Alkanes(Reduction of Alkenes/Alkynes), Preparation of Alkanes(Corey House Reaction, Reduction of Alkyl Halides by LiAlH4, Wurtz Reaction) is considered one of the most asked concept.
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47 Questions around this concept.
Solve by difficulty
Butene-1 may be converted to butane by reaction with
The total number of $\pi$ -bond electrons in the following structure is:
Given:
The enthalpy of the hydrogenation of these compounds will be in the order as:
Which one of the following is reduced with zinc and hydrochloric acid to give the corresponding hydrocarbon?
Reaction of ROH with R'MgX produces:
The treatment of $\mathrm{CH}_3 \mathrm{MgX}$ with $\mathrm{CH}_3 \mathrm{C} \equiv \mathrm{C}-\mathrm{H}_{\text { }}$ produces
In which of the following reactions H2O2 acts as a reducing agent ?
(a)
(b)
(c)
(d)
In the following reaction
$\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{Br} \xrightarrow[\mathrm{H}_{30+}]{\text { 1.mg/ether }} \mathrm{X}$
the product 'X' is:
Phenyl magnesium bromide reacts with methanol to give
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The above reaction follows which mechanism?
Concepts Covered - 5
Preparation of Alkanes(Reduction of Alkenes/Alkynes)
Dihydrogen gas adds to alkenes and alkynes in the presence of finely divided catalysts like platinum, palladium or nickel to form alkanes. This process is called hydrogenation. These metals adsorb dihydrogen gas on their surfaces and activate the hydrogen – hydrogen bond. Platinum and palladium catalyse the reaction at room temperature but relatively higher temperature and pressure are required with nickel catalysts.
Preparation of Alkanes(Hydroboration Reaction)
Diborane(B2H6) adds to an olefinic bond forming trialkylborane which on treatment with acetic acid or propionic acid yields the corresponding alkane.
It is an important method for preparing alkane from alkene. Methane cannot be prepared by this method.
preparation of Alkanes(Grignard Reagent)
Alkyl magnesium halides(RMgX) are called Grignard reagents. These undergo double decomposition reactions with water or ammonia or alcohol or amine having active H atom(attached to strongly electronegative O, N, S or F and triple bond, etc.) to give alkane corresponding to alkyl group of Grignard reagent. The reaction occurs as follows:
Preparation of Alkanes(Corey House Reaction, Reduction of Alkyl Halides by LiAlH4, Wurtz Reaction)
Corey House Synthesis
It is suitable for the preparation of alkanes with odd number of carbon atoms by the following SN2 mechanism.
For example:
Reduction by LiAlH4
In this reaction, alkyl halides are reacted with LiAlH4 (strong reducing reagent) to reduce to alkanes. The reaction occurs as follows:
Wurtz reaction
Alkyl halides on treatment with sodium metal in dry ethereal (free from moisture) solution give higher alkanes. This reaction is known as Wurtz reaction and is used for the preparation of higher alkanes containing even number of carbon atoms.
Preparation of Alkanes(Decarboxylation and Kolbe's electrolysis)
Decarboxylation of Fatty acids
When anhydrous sodium salt of fatty acid is fused with soda lime (NaOH +CaO) a paraffin dry ether having one carbon atom less than the fatty acid is acid. The reaction occurs as follows:
For example:
Kolbe's Electrolysis
Sodium or potassium salts of carboxylic acids on electrolytic hydrolysis give alkanes at anode as follows:
For example:
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Preparation of Alkanes(Reduction of Alkenes/Alkynes)
Preparation of Alkanes(Hydroboration Reaction)
preparation of Alkanes(Grignard Reagent)
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