Exams › JEE Advanced › Chemistry

In which of the following pairs is the indicated (central) carbon-carbon single bond of GREATER strength in the first species than in the second?

1. CH3-CH2-Br vs CH3-CH2-Cl
2. CH3-CH=CH-Br vs CH3-CH(Br)-CH3
3. CH3-COCl vs CH3-CH2-Cl
4. CH2=CH-CH=CH2 (the central C2-C3 bond) vs CH2=CH-CH2-CH3 (the C2-C3 bond)

Correct answer: CH2=CH-CH=CH2 (the central C2-C3 bond) vs CH2=CH-CH2-CH3 (the C2-C3 bond)

Solution

The central C2-C3 single bond of 1,3-butadiene is an sp2-sp2 bond with extra strength from conjugative (partial double-bond) character, whereas the corresponding C2-C3 bond in 1-butene (CH2=CH-CH2-CH3) is an sp2-sp3 bond with no conjugation. Higher s-character plus partial pi delocalisation makes the butadiene central bond shorter and stronger.

Related JEE Advanced Chemistry questions

• When N₂ is converted to N₂⁺, what happens to the bond dissociation energy of the N–N bond, and when O₂ is converted to O₂⁺, what happens to the bond dissociation energy of the O–O bond?
• In which of these ions is pπ–dπ bonding absent?
• What is the VSEPR formula for the chlorine trifluoride molecule?
• Consider the following molecules: CO2, SO2, and H2O. Arrange them in ascending order of their dipole moments.
• Which of the following occurrences is primarily influenced by hydrogen bonding?
• When two 1s atomic orbitals (one from each atom) combine to form molecular orbitals, which of the following statements is correct?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →