Test: JEE Previous Year Questions- Hydrocarbons - JEE MCQ

The correct answer is option B

In HOCl, Cl acts as a cation and OH acts as an anion. First Cl⁺ attacks the aleke to form an electron deficient species(dueto repulsion, OH^- can’t attack). Then OH^- attacks to form compound a.

The correct answer is option B
Acetylene does not react with NaOH because the product will be stronger acid H2​O and the stronger basic salt (CH≡CNa⁺)
Formation of a strong acid is not possible in acid-base neutralisation reaction of a weak acid. Hence, acetylene will not react with NaOH.
 

The number of monohalogenation products obtained from any alkane depends upon the number of different types of hydrogen it contains. Compound containing one type of hydrogen gives only one monohalogen product.

Out of the options, neopentane has only one type of hydrogen.

Alkenes can be converted to alkanes by addition of hydrogen (H₂). In a hydrogenation reaction, two hydrogen atoms are added across the double bond of an alkene, resulting in a saturated alkane. The reaction occurs in the presence of a catalyst like nickel, platinum or palladium.

The correct option is B.

Dehydration of alcohol to alkene in presence of concentrated H₂SO₄ involves the –OH group in the alcohol that donates two electrons to H⁺ from the acid reagent, forming an alkyloxonium ion. The deprotonated acid (the nucleophile) then attacks the hydrogen adjacent to the carbocation and form a double bond.

Thus, the initiation step is protonation of alcohol.

The correct option is C.

The boiling point is in the following order

Alkyne> Alkene> n-Alkane> Branched alkane

1-butyne>1-butene> n-butane> isobutane

Option D is correct.

The correct answer is Option A.

Under mild conditions (temperature ≈ - 80°C) kinetic product is the 1, 2-addition product and under vigorous conditions. (temp. ≈ 40°C) thermodynamic product is the 1 , 4-addition product. Thus, 1-bromo -2 - butene is the major product under given condition.

The correct answer is option D
Alkyl halides react with dialkyl copper reagents to give alkanes. The reaction is called Corey House synthesis.
R2​CuLi+R′X→R−R′+RCu + LiX
For example, ethyl iodide reacts with lithium diethyl cuprate to form butane.
(C_2​H₅​)₂​CuLi+C₂​H₅​−I→C₂​H₅​−C₂​H₅​+C₂​H₅​Cu + LiI

In elimination reaction of alkyl halide major product is obtained according to Saytzeff’s rule, which states that when two alkenes may be formed, the alkene which is most substituted one predominates.

The given compound is the result of Hofmann Exhaustive Methylation reaction.
According to Hofmann Rule the less substituted alkene is the major product.


Hence CH₂ = CH₂ will be the major product with

From aniline by diazotisation followed by heating the diazonium salt with HBF₄

The reaction of methanol with phenyl magnesium bromide is:

CH₃OH + C₆H₅MgBr → C₆H₆ + Mg(OCH₃)Br

A mixture of benzene and Mg(OMe)Br is obtained.

The correct option is A.

The correct answer is option  A
Reaction of propyne with 2 molecules of HBr to form 2,2 -dibromine propane can be written as:
CH₃ − C ≡ CH + 2HBr → CH₃​ − C(Br) = CH_2​
CH₃​ − C(Br) = CH_2​ + HBr → CH_3​ − C(Br)_2​ − CH_3​
The reaction follows Markownikoff's rule.

The correct answer is option C
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Here, Grignard reagent acts as base and acid base reaction occurs (as hydrogen of sp hybridized C atom acts as acid). So CH₃- takes H+ and forms CH₄.

The correct answer is option  A
1-butyne can react with sodium in liquid ammonia. Because terminal alkynes have acidic hydrogen. This acidic hydrogen can replace Na in presence of liquid ammonia.

 

Presence of one vinyl group gives formaldehyde as one of the product in ozonolysis.

Ozonolysis breaks the double bond and oxidizes that carbon. To solve these questions, when the reactants are asked, just remove the carbonyl oxygen from the products and join the resulting compounds using a double bond. 

The correct answer is option A
2-hexyne with Li/NH3​ gives trans-2-hexene. This reaction is also considered as Birch reduction.