Steric Enhancement of Resonance—Evidence from Ultraviolet Spectral Study on some Halogeno- and Nitro-methoxyacetophenones

Department of Chemistry, Bharathidasan University, Tiruchirapalli-620 024

Manuscript received 8 January 1986, revised 23 July 1987, accepted 22 august 1987

The uv spectral study on some halogeno- and nitro-methoxyaceto-­phenones furnishes evidence for the phenomenon of steric enhancement of resonance. There occurs a red-shift of ¹L_a band when a halogen Is present in the position \(ortho\) to the methoxyl group in 4-methoxyacetophenone. The oscillator strength increases from acetophenone to 4-methoxyaceto-­phenone and then to 3-halogeno- and 3-nitro-4-methoxyacetophenones The spectral data of the above compounds lend support for the concept of steric enhancement of resonance.