Nonanoic acid, also called pelargonic acid, is an organic compound composed of a nine-carbon chain terminating in a carboxylic acid with structural formula CH₃(CH₂)₇COOH. Nonanoic acid forms esters—nonanoates. It is a clear, oily liquid with an unpleasant, rancid odor. It is nearly insoluble in water, but very soluble in chloroform, ether, and hexane. It is commonly used in conjunction with glyphosate, a non-selective herbicide, for a quick burn-down effect in the control of weeds in turfgrass.