Q65 · CSIR-NET Chemistry, June 2013
Paper: CSIR-NET June 2013 · Subject: Organic Chemistry · Chapter: Organic Spectroscopy · Topic: Organic Spectroscopy – General · Marks: 2 · Difficulty: Medium
In the UV-visible is spectrum, a diterpenoid exhibited $\lambda_{\max}=275 \mathrm{nm}$. The compound, among the choices given below is
(a)
(b)
(c)
(d)
Answer
Answer: C ✓ checked by 4AB · confidence medium
Explanation
λmax 275 nm requires a homoannular (both double bonds in one ring) diene: base 253 + alkyl substituents/ring residues ≈ 273–278 nm. This is levopimaric-type (c); heteroannular dienes absorb near 235–245 nm.
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