Question

Which of the following statements is not correct for sigma and pi-bonds formed between two carbon atoms?
A. A sigma bond is stronger than a pi-bond.
B. Bond energies of sigma and pi-bonds are of the same order.
C. Free rotation of atoms about a sigma bond is allowed but not in case of a pi-bond.
D. A sigma bond determines the direction between carbon atoms, but a pi-bond has no primary effect in this regard.

Answer 1

Hint : A sigma bond is able to determine the position correctly between the carbon atoms, however Bond energies may need to be checked. A sigma bond is actually the strongest type of covalent chemical bond.

Complete Step By Step Answer:
A) A sigma bond is quite stronger than a pi-bond. This is due to sigma bond is produced by axial overlap and pi bond is produced by lateral overlap. Therefore the extent of overlap is higher in sigma bond formation than in pi bond formation.
Hence, the option A is correct.
B) Sigma bond has bond energy higher than that of pi bond because sigma bond is quite stronger than pi bond.
Hence, the option B is not correct.
C) Free rotation of atoms about a sigma bond is allowed, however not allowed in the case of a pi-bond. Whenever the carbon atoms of sigma bonds are used to rotate, the axial overlap does not get affected. Although in the case of pi bonds, the lateral overlap will get affected.
Hence, the option C is correct.
D) A sigma bond determines the direction between carbon atoms, but a pi-bond has no primary effect in this regard. A pi bond exists only when a sigma bond is already present there.
So, Answer is Option (B) is not correct.
Hence, the option D is correct.

Additional Information:
Sigma bonds (σ bonds) are actually the strongest type of covalent chemical bond. They are produced by head-on overlapping b/w atomic orbitals. Sigma bonding can be defined most simply for diatomic molecules by using the language and tools of symmetry groups.
Pi bonds (π bonds) are actually covalent chemical bonds where 2 lobes of an orbital on 1 atom overlap 2 lobes of an orbital on another atom and this overlap occurs laterally. Each of these atomic orbitals actually has 0 electron density at a shared nodal plane, going through the 2 bonded nuclei.

Note :
By observing the hint and the given options, answers can be determined easily. Sigma bond has bond energy actually higher than that of pi bond as sigma bond is quite stronger than pi bond as Sigma bonds are actually the strongest type of covalent chemical bond.