Paper: CSIR-NET December 2018 · Subject: Physical Chemistry · Chapter: Group Theory · Topic: Character Tables · Marks: 2 · Difficulty: Medium
Under review — part of this question (a structure or an option) is not clear in the source scan. 4AB is checking it against the original book; the answer shown may change.
The -orbital $\pi_u$ of ethylene, when placed in the $xy$-plane with the $C=C$ bond aligned to the $x$-axis, transforms according to the irreducible representation (Use Table-1)
(a)$a_u$
(b)$b_{1u}$
(c)$b_{2u}$
(d)$b_{3u}$
Answer
Under review — not yet confirmed.
Answer: B
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
With the molecule in the xy-plane and C=C along x, the bonding π orbital is built from p_z. In D₂h it transforms like z, i.e. b₁u (b).