1. Fourth letter of the Greek alphabet, delta. 2. In chemistry, denotes a double bond, usually with a superscript to indicate position in a chain (DELTA5); application of heat in a reaction (A ->DELTA B); absence of heat treatment (&o); distance between two atoms in a molecule; or position of a substituent located on the fourth atom from the carboxyl or other primary functional group (delta); change (DELTA); thickness (delta); chemical shift in NMR (delta).
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