This question involves identifying the product (Y) formed in a reaction, with the given image showing a reaction scheme. Based on the options provided (1-butene, trans-2-butene, Iso-butene, cis-2-butene), this is a classic problem in organic chemistry concerning the dehydration of alcohols and the stability of alkenes.

Step 1: Understand the Reaction

The reaction shown is the acid-catalyzed dehydration of an alcohol. The most common example is the dehydration of butan-2-ol. Dehydration involves the removal of a water molecule (H $O$ ) from the alcohol, resulting in the formation of an alkene.

The general reaction is:

$R - CH 2 - CH 2 - OH \overset{H^{+}, Δ}{\to} R - CH = CH 2 + H_{2} O$

Step 2: Apply it to the Specific Case

For butan-2-ol ( $CH 3 - CH 2 - CH (OH) - CH 3$ ), this is a secondary alcohol. Dehydration can follow two pathways due to the unsymmetrical nature of the molecule, leading to a mixture of alkene isomers.

The possible products are:

1-Butene ( $CH 2 = CH - CH 2 - CH 3$ )
2-Butene, which exists as two stereoisomers: cis-2-butene and trans-2-butene.

Step 3: Determine the Major Product (Saytzeff's Rule)

Saytzeff's Rule states that in elimination reactions, the more highly substituted alkene (the alkene with more alkyl groups attached to the carbon atoms of the double bond) is the major product. More substituted alkenes are more stable.

1-Butene is monosubstituted (it has one alkyl group on one of the double-bond carbons).
2-Butene is disubstituted (each carbon of the double bond has one alkyl group).

Therefore, 2-butene is the major product. Between cis and trans isomers of 2-butene, the trans isomer is more stable than the cis isomer due to less steric strain between the two methyl groups.

Step 4: Final Answer

The major product (Y) of the acid-catalyzed dehydration of butan-2-ol is the more stable alkene, which is trans-2-butene.

Final Answer: trans-2-butene

Related Topics & Formulae

Key Concepts

Dehydration of Alcohols: An elimination reaction where an alcohol loses a water molecule to form an alkene, catalyzed by acids like H ${SO}_{4}$ .
Saytzeff's Rule (Zaitsev's Rule): Predicts that the major product in β-elimination is the more highly substituted, and therefore more stable, alkene. Stability order: Tetra-substituted > Tri-substituted > Di-substituted > Mono-substituted.
Stability of Alkenes: Trans alkenes are generally more stable than their cis counterparts due to reduced steric hindrance.

Important Reaction

General Dehydration Reaction: $R - CH 2 - CH 2 - OH \overset{H^{+}, Δ}{\to} R - CH = CH 2 + H_{2} O$