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Step-by-Step Explanation
Step 1: Identify the products formed from 2-butyne
2-butyne ($CH_3 - C \equiv C - CH_3$) undergoes partial hydrogenation in two different ways:
1. Treatment with $H_2$ in the presence of Lindlar's catalyst forms the cis-alkene (cis-2-butene). This product is labeled as X.
2. Treatment with Na in liquid $NH_3$ gives the trans-alkene (trans-2-butene). This product is labeled as Y.
Step 2: Structure and polarity considerations
• In cis-2-butene (X), both methyl groups are on the same side of the double bond. The arrangement of substituents does not completely cancel out the bond dipoles, so there is a net dipole moment.
• In trans-2-butene (Y), the methyl groups are on opposite sides of the double bond, causing dipole moments to cancel each other out, resulting in a very small net dipole moment.
Step 3: Correlation of dipole moments to boiling points
A higher net dipole moment generally leads to stronger intermolecular dipole–dipole interactions. This in turn increases the boiling point. Hence:
• cis-2-butene (X) has a higher dipole moment and thus a higher boiling point.
• trans-2-butene (Y), with minimal net dipole moment, has a lower boiling point.
Step 4: Conclusion
Therefore, compound X (cis-2-butene) possesses both a higher dipole moment and a higher boiling point compared to compound Y (trans-2-butene). This matches the correct statement: “X will have higher dipole moment and higher boiling point than Y.”
Reference Image
Step-by-Step Explanation
Step 1: Identify the products formed from 2-butyne
2-butyne ($CH_3 - C \equiv C - CH_3$) undergoes partial hydrogenation in two different ways:
1. Treatment with $H_2$ in the presence of Lindlar's catalyst forms the cis-alkene (cis-2-butene). This product is labeled as X.
2. Treatment with Na in liquid $NH_3$ gives the trans-alkene (trans-2-butene). This product is labeled as Y.
Step 2: Structure and polarity considerations
• In cis-2-butene (X), both methyl groups are on the same side of the double bond. The arrangement of substituents does not completely cancel out the bond dipoles, so there is a net dipole moment.
• In trans-2-butene (Y), the methyl groups are on opposite sides of the double bond, causing dipole moments to cancel each other out, resulting in a very small net dipole moment.
Step 3: Correlation of dipole moments to boiling points
A higher net dipole moment generally leads to stronger intermolecular dipole–dipole interactions. This in turn increases the boiling point. Hence:
• cis-2-butene (X) has a higher dipole moment and thus a higher boiling point.
• trans-2-butene (Y), with minimal net dipole moment, has a lower boiling point.
Step 4: Conclusion
Therefore, compound X (cis-2-butene) possesses both a higher dipole moment and a higher boiling point compared to compound Y (trans-2-butene). This matches the correct statement: “X will have higher dipole moment and higher boiling point than Y.”
Reference Image
