activating group acylation alfred einhorn alkyl alkylation aluminium chloride amide aniline arenium ion aromatic sulfonation aromaticity aryl asymmetric synthesis benzaldehyde benzene bischler-napieralski reaction bisoxazoline ligand bromine carbocation carbon dioxide carbonyl chloral chlorine crotonaldehyde deactivating groups digital object identifier directed ortho metalation electrophile enantiomeric excess friedel-crafts reaction functional group furan halogen hayashi rearrangement hydrogen imidazole indole inductive effect iodine kolbe-schmitt reaction lehmstedt-tanasescu reaction nitration nitric acid nitro nitro compound nitrobenzene nitrogen organic reaction oxygen pechmann condensation phenol phenols phosphoric acid picric acid pictet-spengler reaction prochiral pyrrole reaction mechanism reaction rate regioselectivity reimer-tiemann reaction salicylic acid substituent sulfur sulfuric acid thiophene toluene trifluoroacetic acid trinitrotoluene vilsmeier-haack reaction