Question

Which of the following statements is/are not correct?

• A. $\pi$ - bond always exists with sigma -bond according to Valence Bond Theory
• B. $\pi$ - bond can exist independently according to Valence Bond Theory
• C. $\sigma$ - bond is weaker than pi-bond
• D. $\pi$ - bond is less reactive than sigma-bond

Answer 1

Answer: (B), (C), (D)

The correct options are
B $\pi$ - bond can exist independently according to Valence Bond Theory
C $\sigma$ - bond is weaker than pi-bond
D $\pi$ - bond is less reactive than sigma-bond

(A) $\pi -$ bond always exists with sigma-bond according to Valence Bond Theory.

(B) $\pi -$ bond cannot exist independently.

(C) Sigma-bond is not weaker than pi-bonds. Rather $\pi$ bond are usually weaker than sigma bonds. Quantum mechanics says this is because the orbital paths are parallel so there is much less overlap between the p-orbitals. $\pi$ bonds happen when two atomic orbitals are in contact through two areas of overlap.

(D) Unsaturated compounds (containing pi bonds due to the existence of a double bond) are more reactive than saturated compounds (containing only sigma bonds) because the electron density at the internuclear axis is zero in a $\pi$ bond ( in contrast to the sigma bond). $\pi$ bonds involve sideways overlap while sigma bond involves a head-on or axial overlap.