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Which of the following statements regarding indigotin (indigo dye) is INCORRECT?

1. It exhibits geometrical isomerism
2. The trans isomer is more stable than the cis isomer
3. The cis isomer is more stable than the trans isomer
4. The molecule has a planar structure

Correct answer: The cis isomer is more stable than the trans isomer

Solution

Indigotin does show geometrical isomerism and is a planar molecule. The trans isomer is the stable natural form due to intramolecular hydrogen bonding between N-H and C=O groups; the claim that cis is more stable is incorrect.

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