Chemistry · Ch 11 — Fundamentals of Organic Chemistry
Classification Based on Structure
Classification Based on Structure
Structurally, every organic compound is either acyclic (an open, unbranched-or-branched chain, also called aliphatic) or cyclic (containing at least one ring). Propane, CH3-CH2-CH3, is the textbook example of an acyclic compound -- there is no ring anywhere in the molecule.
Cyclic compounds split further by what the ring is made of. A ring built ENTIRELY of carbon atoms is homocyclic; a ring containing at least one non-carbon atom (commonly O, N or S) is heterocyclic. Each of those, in turn, splits by whether the ring is aromatic or not. Among homocyclic rings: an alicyclic (or carbocyclic) ring is a plain, non-aromatic carbon ring, such as cyclopropane; an aromatic homocyclic ring is either benzenoid (built around an actual benzene ring, such as phenol) or non-benzenoid (aromatic by virtue of its electron system despite not containing a benzene ring, such as azulene, a fused five-and-seven-membered ring system). Among heterocyclic rings: an alicyclic heterocycle is a non-aromatic ring containing a heteroatom, such as tetrahydrofuran (THF, a five-membered ring with one ring oxygen); an aromatic heterocycle is an aromatic ring containing a heteroatom, such as pyridine (a six-membered ring with one ring nitrogen). …
What this figure shows. A flowchart headed 'Organic Compounds' branching into 'Acyclic or open chain or aliphatic compounds' (example: CH3-CH2-CH3, propane) and 'Cyclic compounds'. Cyclic compounds branch into 'Homocyclic compounds' and 'Heterocyclic compounds'. Homocyclic compounds branch into 'Alicyclic Compounds or carbocyclic' (drawn as cyclopropane, a 3-membered ring of CH2 units) and 'Aromatic compounds', which further split into 'Benzenoid compounds or aromatic homocyclic' (drawn as phenol, a benzene ring bearing -OH) and 'Non-Benzenoid compounds also aromatic homocyclic' (drawn as azulene, a fused 5-7 ring system). Heterocyclic compounds branch into 'Alicyclic compounds' (drawn as THF, a 5-membered ring with one ring oxygen) and 'Aromatic compounds' (drawn as pyrid …