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Webster 1828 Edition

pp.

s as z.

Noticed by the eye or the mind.

Kept religiously; celebrated; practiced.

observed

simple past tense and past participle of observe
Aldrichimica Acta Volume 30 No 4 (pdf) from Sigma-Aldrich
N-substituted pyrroles are much less reactive than the other 5-membered 1,3-dienes; no reaction was observed between N-(trimethylsilyl) pyrrole or N-benzylpyrrole with Smith’s diene (4) under thermal or high pressure (4 days at 14 kbar) conditions, even in the presence of Lewis acids.