Deuterated dicondensed indolinobenzospiropyran formed from the reaction of Fischer base-d2 and salicylaldehyde: Mechanism involving a carbinol intermediate

From the deuterium content (x-value) of deuterated molecules obtained from the reaction of an excess of Fischer base-d2 with salicylaldehydes, it is found that the formation of the dicondensed indolinobenzospiropyrans occurred via a carbinol intermediate, rather than an open merocyanine form of spiropyran. 1H NMR behavior supported this proposed mechanism, indicating that a carbinol intermediate was simultaneously, and not consecutively, formed prior to the transformation to both spiropyrans and dicondensed indolinobenzospiropyran.