Many ketones are cyclic. The simplest class have the formula , where n varies from 2 for cyclopropanone () to the tens. Larger derivatives exist. Cyclohexanone (), a symmetrical cyclic ketone, is an important intermediate in the production of nylon. Isophorone, derived from acetone, is an unsaturated, asymmetrical ketone that is the precursor to other polymers. Muscone, 3-methylpentadecanone, is an animal pheromone. Another cyclic ketone is cyclobutanone, having the formula .