label: trans-2-chloro-4-carboxymethylenebut-2-en-1,4-olide => cis-2-chloro-4-carboxymethylenebut-2-en-1,4-olide
label_lc: trans-2-chloro-4-carboxymethylenebut-2-en-1,4-olide => cis-2-chloro-4-carboxymethylenebut-2-en-1,4-olide