Complex sentence: "Trans-cis isomerism" is where, in certain compounds, an interconversion of cis and trans isomers can be observed, for instance, with maleic acid and with azobenzene often by photoisomerization.
Split into simpler sentences: Trans-cis isomerism is where, in certain compounds, an interconversion of cis and trans isomers can be observed. For instance, with maleic acid and with azobenzene, often by photoisomerization.