2,4,5,6,7,7a-Hexahydro-4,7-methano-1H-inden-5(or 6)-yl isobutyrate 68900-66-3 Dicyclopentadiene isobutyrate EINECS 272-619-6 Propanoic acid, 2-methyl-, 2,4,5,6,7,7a-hexahydro-4,7-methano-1H-inden-5(or 6)-yl ester