Upon introduction of the nitrothiop

Upon introduction of the nitrothiophenol to the benzoxazine, the mixture instantlyturns blood red. The same color change is observed when nitrothiophenol is exposed to a base; the deep-red color is an indicator of the formation of the p-nitrothiophenoxideanion [27,28]. The anion is deeply colored because the S– of the thiophenoxide is an excellent electron donor,and the nitro group is one of the best electron acceptor species. The color is the indicator of the delocalized charge in the p-nitrothiophenoxide anion.