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...Heterocycles cyclic organic compounds are carbocycles or carbocycle rings contain only carbon atoms heterocycle in addition to n s o common include many important natural materials as well pharmaceuticals five membered unsaturated pyrrole furan and thiophene each has two double bonds commercially from coal tar by treatment of with ammonia over an alumina catalyst at c made extrusion co furfural which is produced sugars cyclization butane butadiene sulfur...