Phenolphthalein (HIn - colorless form)

 Phenolphthalein (In- - pink form)

Color Codes
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C

H

N

O

P

S

Cl

F
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  Optimal View    Move manually to match left window Notice double bond connecting center carbon to one ring and a "flattening" of the structure.
  Spacefill / ball & stick  Changes / ball & stick   Spacefill / ball & stick   Changes / ball & stick
  Wireframe / ball & stick   Wireframe / ball & stick Pink form has lost a hydrogen on a phenol (alcohol) and formed negative ion on carboxyl group.