Wikipedia
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 CHO, is distinctly different from its more prevalent isomer, vanillin. The " ortho-" prefix refers to the position of the compound’s hydroxyl moiety, which is found in the para-position in vanillin.
ortho-Vanillin is a fibrous, light-yellow, crystalline solid. Unlike its better-known analogue, o-vanillin does not have the characteristic and intense odor of vanilla. Present in a variety of food products, it is not specifically sought after, and is therefore a less-commonly produced and encountered food additive.