Wiktionary
isophthalic acid
n. (context organic compound English) The isomer of phthalic acid ''benzene-1,3-dicarboxylic acid'' used in the synthesis of polymers
Wikipedia
Isophthalic acid
Isophthalic acid is an organic compound with the formula CH(COH). This colourless solid is an isomer of phthalic acid and terephthalic acid.