Sentence:  On the other hand, ^1\mathrm O_2 is known to be a selective oxidant that reacts with electron-rich olefins, <WSD>conjugated</WSD> dienes, sulfides and phenols. 
Meaning of the word marked with <WSD> tags:  Of an organic compound or part of such a compound, containing one or more pairs of double bonds and/or lone pairs, each pair being separated by a single bond.