Question

Which is correct statement about $\sigma -$ and $\pi -$ molecular orbitals? Statements are
(i) $\pi -$ bonding orbitals are ungerade
(ii) $\pi -$ antibonding orbitals are ungerade
(iii) $\sigma -$ antibonding orbitals are gerade

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

Answer 1

Answer: (A)

(i) only

The symmetry of molecular orbital is detemined by rotating the orbitals about a line perpendicular to it. If the sign of the lobes remains the same, the orbital is gerade and if the sign changes, the orbital is ungerade. $\pi$ bonding orbitals are ungerade whereas $\pi$ antibonding orbitals are gerade. Also $\sigma$- antibonding orbitals are ungerade