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NEET CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques Medium

Question

The incorrect statement among the following for sigma- (σ\sigma) and pi- (π\pi) bonds formed between two carbon atoms is:

A

Sigma-bond is stronger than a pi-bond

B

Bond energies of sigma- and pi-bonds are of the order of 264 kJ/mol and 347 kJ/mol, respectively

C

Free rotation of atoms about a sigma bond is allowed but not in the case of a pi-bond

D

Sigma-bond determines the direction between carbon atoms but a pi-bond has no primary effect in this regard

Step-by-Step Solution

To identify the incorrect statement, we analyze the properties of sigma and \pi bonds based on chemical principles and the provided sources:

  1. Strength: A sigma bond is stronger than a \pi bond because it is formed by the head-on overlap of atomic orbitals, which results in a greater extent of overlapping .
  2. Bond Energies: According to the sources, the bond enthalpy of a carbon-carbon single bond (which is a sigma bond) is approximately 347 kJ/mol . In a double bond, the \pi bond is weaker, with a bond enthalpy of approximately 284 kJ/mol . Therefore, the statement claiming the sigma bond is 264 kJ/mol and the \pi bond is 347 kJ/mol is incorrect because it misstates the values and implies the \pi bond is stronger.
  3. Rotation: Sigma bonds allow for free rotation of atoms around the bond axis because the electron distribution is symmetrical around the internuclear axis . However, rotation about a \pi bond is restricted because it would disrupt the parallel orientation of p-orbitals required for sideways overlap .
  4. Directionality: Sigma bonds are formed by axial overlap along the internuclear axis and determine the geometry and primary direction of the bond between atoms . Pi bonds are formed by lateral overlap and do not primarily determine the direction of the bond .

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Organic Chemistry – Some Basic Principles and Techniques . Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYOrganic Chemistry – Some Basic Principles and Techniques incorrectstatementfollowingformedbetween

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