Question

Which is the correct statement about sigma and pi molecular orbitals? Statements are (i) π bonding orbitals are ungerade (ii) π antibonding orbitals are ungerade (iii) σ antibonding orbitals are gerade

• A. (i) only
• B. (ii) and (iii)
• C. (iii) only
• D. (ii) only

Answer 1

The correct option is A

(i) only

Explanation for correct option

(A) (i) only

• Rotating the orbitals about a line parallel to it give information about the symmetry of the molecular orbital.
• The orbital is gerade if the sign of the lobes stays the same.
• The orbital is ungerade if the sign changes.
• The diagram of bonding pi orbital is as follows:-
• 
• In the given diagram, above the point, there is a positive wave function and below the point, there is a negative wave function. Thus, there is no center of symmetry. Thus, π-bonding orbitals are ungerade.
• The diagram of the antibonding pi orbital is as follows:-
• 
• In the given diagram, there is a center of symmetry. Thus, π-antibonding orbitals are gerade.
• The diagram of the sigma antibonding is as follows:-
• 
• In the given diagram, there is no center of symmetry. Thus, σ-antibonding orbitals are ungerade.

Explanation for incorrect options

π antibonding orbitals are gerade. Sigma Antibonding orbitals are ungerade. Hence, the options (B), (C), (D) are incorrect.

Hence, option (A) is correct.π bonding orbitals are ungerade