Chemistry · Ch 14 — Basic Principles of Organic Chemistry
Classification based on carbon skeleton
Classification based on carbon skeleton
Classification by carbon skeleton looks purely at how a molecule's own carbon atoms are bonded to one another -- this bonded network is called the carbon skeleton, and it is what fundamentally decides the molecule's overall shape and size. ACYCLIC (open-chain) compounds, also called ALIPHATIC compounds, have their carbon atoms arranged in an open, non-ring chain; this chain can be a STRAIGHT chain (every carbon bonded to at most two other carbons, so the chain never branches, e.g. propane CH3-CH2-CH3 or n-propyl alcohol CH3-CH2-CH2-OH) or a BRANCHED chain (at least one carbon bonded to three or four other carbons, so the chain forks, e.g. isobutane CH3-CH(CH3)-CH3). CYCLIC compounds instead have their atoms joined together into a closed ring. Where that ring is made up ENTIRELY of carbon atoms, the compound is called HOMOCYCLIC or CARBOCYCLIC; where the ring instead includes one or more HETEROATOMS (any ring atom that is not carbon -- oxygen, nitrogen, and sulfur are the commonest examples), the compound is called HETEROCYCLIC. Within the homocyclic/carbocyclic compounds, ALICYCLIC compounds are those whose chemical behaviour more closely resembles ordinary open-chain (aliphatic) compounds than it resembles the special stability of an aromatic ring -- cyclobutane and cyclohexene are given as examples. AROMATIC compounds, by contrast, possess a special extra stability not shared by alicyclic rings; those built around an actual six-membered benzene ring are called BENZENOID aromatics (benzene itself, and also naphthalene and phenol, which each still contain a genuine benzene ring within their structure), while those that show aromatic character WITHOUT containing a true benzene ring are called NON-BENZENOID aromatics (tropone, a seven-membered ring bearing a ketone group, is the example given). Heterocyclic compounds are likewise split by whether or not they show this special aromatic stability: heterocyclic NON-AROMATIC examples include tetrahydrofuran (THF, a saturated five-membered oxygen-containing ring), piperidine (a saturated six-mem …
Table 14.2 gives two straight-chain examples -- propane, CH3-CH2-CH3, and n-propyl alcohol, CH3-CH2-CH2-OH -- alongside one branched-chain example, isobutane, CH3-CH(CH3)-CH3, illustrating the straight-chain vs branched-chain distin …
What this figure shows. A classification tree starting from 'Organic compounds' and branching first into Acyclic/Aliphatic (open chain) versus Cyclic (closed chain). The Cyclic branch splits into Homocyclic (carbocyclic) and Heterocyclic. The Homocyclic branch splits further into Alicyclic and Aromatic; the Aromatic sub-branch further splits into Benzenoid aromatic and Non-benzenoid aromatic. The Heterocyclic branch splits into Heterocyclic Aromatic and Heterocyclic Non-Aromatic. This tree is the master diagram summarising every carbon-skelet …
What this figure shows. Three labelled example groups: (a) alicyclic compounds -- cyclobutane (a simple four-membered saturated carbon ring) and cyclohexene (a six-membered carbon ring containing one C=C double bond); (b) benzenoid aromatic compounds -- naphthalene (two fused benzene rings) and phenol (a benzene ring bearing a single -OH substituent); (c) non-benzenoid aromatic compounds -- tropone (a seven-membered ring bearing a ketone, aromatic in character despite containing no six-me …
What this figure shows. Two labelled groups of heterocyclic ring structures. Heterocyclic non-aromatic compounds: tetrahydrofuran (THF, a saturated five-membered ring with one oxygen), piperidine (a saturated six-membered ring with one nitrogen, bearing an N-H), and 4H-pyran (a six-membered ring with one oxygen and one point of unsaturation). Heterocyclic aromatic compounds: furan (a five-membered aromatic ring with one oxygen), thiophene (the sulfur analogue of furan), pyrrole (a five-membered aromatic ring with one N-H nitrogen), and pyridine (a six-membered aromatic …