Benzene is an important organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals. Because of the cyclic continuous pi bond between the carbon atoms, benzene is classed as an aromatic hydrocarbon, the second [n]-annulene ([6]-annulene).
Synthetic round slings offer a number of advantages for rigging purposes. The most commonly used synthetic round slings are made of nylon- or polyester-type yarns. Each synthetic material has its own unique properties. Certain synthetic materials perform better than others in specific applications and environments.
Historically, ropes have been made out of whatever fibers were available. Therefore, ancient versions were often made of silk fibers, animal fur, even human hair. It is likely that the first that were ever used were simply plant vines.