Periinteraction in several naphthalene ketones was investigated using the carbon-13 NMR, IR, and UV spectra. The carbonyl carbon resonances for 7H, 14H-cycloocta[1,2,3-de:5,6,7-d′e′]dinaphthalene-7,14-dione and its 7-oxa analog were found to be shifted upfield by 27 and 24 ppm respectively compared with those of model compounds. The anomalous shift for the former was attributed to π-orbital compression