Test: JEE Previous Year Questions- Alcohols - JEE MCQ

• Dehydration of Alcohols: Dehydration involves removing a water molecule from an alcohol to form an alkene. The ease of dehydration follows the order: tertiary > secondary > primary alcohols due to carbocation stability.
• Carbocation Stability: Option B forms a carbocation stabilized by resonance with a carbonyl group (C=O), enhancing stability and promoting dehydration.
• Conjugation with (C=O): The resultant alkene in option B is conjugated with a carbonyl group, increasing its stability, thus promoting dehydration further compared to other options.

The correct answer is option D

When CH₂=CH−COOH is reduced with LiAlH₄:

CH₂=CH−CH₂OH compound is formed because LiAlH₄ reduces −COOH to CH₂OH without affecting C=C bond. 

The ease of dehydration of alcohols is tertiary > secondary > primary according to the order of stability of the carbocations.

The more stable carbocation is generated, thus more easily it will be dehydrated.

Density of gas = (Mol. wt. × P) / (RT)

Since both isomers have same molecular mass and hence their densities will be same at same temperature and pressure.

Methyl vinyl ether is a very reactive gas. It is hydrolysed rapidly by dilute acids at room temperature to give methanol and aldehyde. However, under anhydrous conditions at room temperature, it undergoes many addition reactions at the double bond.

Electrophilic addition reaction more favourable.

Correct Answer is option C

• When ethanol is treated with a mixture of phosphorus and iodine, ethyl iodide CH₃​CH₂​I is obtained. 
• Compound A on reaction with Mg metal in ether forms ethyl magnesium iodide CH₃​CH₂​ MgI. 
• The compound B reacts with formaldehyde to form compound C; CH_3​CH₂​−CH₂​−OMgX which on hydrolysis gives n propyl alcohol CH₃​CH₂​CH₂​−OH.
• The compound D is n-propyl alcohol. 

 
Hence, option C is correct.

The fruity smell is evolved due to the formation of ester when ethanol and acid are treated in the presence of concentrated H2​SO4​.
The reaction is
CH₃​COOH + CH_3​CH₂​OH → CH₃​COOC₂​H_5​

A mixture of conc.HCl and anhydrous ZnCl₂ is called Lucas reagent.

Primary alcohols react with Lucas reagent very slowly on heating to give alkyl chlorides.
Secondary alcohols react with Lucas reagent much faster.
Tertiary alcohols instantaneously react with HCl at room temperature.
 Note: Lucas reagent is required for primary and secondary alcohol only.

• Whenever dehydration can form two different alkenes major product is formed according to sides of rule that is more substituted alkene or alkene having lesson number of hydrogen atoms on the to double bonded carbon atoms is the major product. 
• Such reactions which can produce two or more structural isomers but one of them in Greater amount than the others are called ratio selective encasa reaction is hundred percent regioselective it is termed as reduce specific
• In addition to being reduced selective alcohol dehydration are stereoselective reaction in which a single starting material can yield two or more stereoisomeric products but give one of them in Greater amount than any other