Salicylaldehyde derivatives

thumb|right|class=skin-invert-image|UV visible spectrum of quercetin, with lambda max at 369 nm

Salicylic aldehyde (2-hydroxybenzaldehyde) is an organic compound with the formula . Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily liquid has a bitter almond odor at higher concentration. Salicylaldehyde is a precursor to coumarin and a variety of chelating agents.

'''ortho-Vanillin' (2-hydroxy-3-methoxybenzaldehyde) is an organic solid present in the extracts and essential oils of many plants. Its functional groups include aldehyde, ether and phenol. ortho-Vanillin, a compound of the formula C8H8O3, is distinctly different from its more prevalent isomer, para-vanillin. The "ortho-" prefix refers to the position of the compound’s hydroxyl moiety, which is found in the para''-position in vanillin.

'''3,5'-Di-tert-butylsalicylaldehyde''' is an organic compound. It is a pale yellow solid. This aldehyde is a building block for preparing salen ligands.