_____are compounds in which the atoms are joined in a ring.
For example, the symmetrical hexacyclic compound coronene has a H/C ratio =1/2, compared with 1 for benzene. If we were to imagine fused ring systems of this kind to be further extended in space, the H/C ratio would approach zero, and the resulting compound would be a form of carbon. Benzene is the archetypical aromatic compound. It is planar, bond angles=120º, all carbon atoms in the ring are sp2 hybridized, and the pi-orbitals are occupied by 6 electrons. The aromatic heterocycle pyridine is similar to benzene, and is often used as a weak base for scavenging protons. Heterocyclic compound. Heterocyclic compound, also called heterocycle, any of a major class of organic chemical compounds characterized by the fact that some or all of the atoms in their molecules are joined in rings containing at least one atom of an element other than carbon (C). Benzene rings may be joined together (fused) to give larger polycyclic aromatic compounds. A few examples are drawn below, together with the approved numbering scheme for substituted derivatives. The peripheral carbon atoms (numbered in all but the last three examples) are all bonded to hydrogen atoms. Aromatic Rings. Aromatic rings (also known as aromatic compounds or arenes) are hydrocarbons which contain benzene, or some other related ring structure. Benzene, C6H6, is often drawn as a ring of six carbon atoms, with alternating double bonds and single bonds: This simple picture has some complications, however. In their general structure, heterocyclic compounds resemble cyclic organic compounds that incorporate only carbon atoms in the rings—for example, cyclopropane (with a three-carbon-atom ring) or benzene (with a six-carbon-atom ring)—but the presence of the heteroatoms gives heterocyclic compounds physical and chemical properties that are often quite ... Fused Benzene Ring Compounds. Benzene rings may be joined together (fused) to give larger polycyclic aromatic compounds. A few examples are drawn below, together with the approved numbering scheme for substituted derivatives. The peripheral carbon atoms (numbered in all but the last three examples) are all bonded to hydrogen atoms. A cyclic compound or ring compound is a compound at least some of whose atoms are connected to form a ring. Rings vary in size from 3 to many tens or even hundreds of atoms. Examples of ring compounds readily include cases where: Cyclic compound. A cyclic compound (ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. The six benzene rings in coronene are fused in a planar ring; whereas the six rings in hexahelicene are not joined in a larger ring, but assume a helical turn, due to the crowding together of the terminal ring atoms.
Heterocyclic are compounds in which the atoms are joined in a ring.