👉 Presubstituted refers to a chemical compound that is not present in the original substance, but exists in a form that is similar or identical to its pure form. This can occur in different forms, such as as a byproduct of a reaction, or as a result of a process used to separate components of the same substance. Presubstituted compounds are often used for analytical purposes and may be useful in identifying substances that have not been properly isolated from their original state.