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V. Organic Oxygen Compounds (continued)
Structural Diagrams
It becomes burdensome and cluttered to represent each atom in complex molecules by atomic symbols C, H, O, etc., accompanied by multiplying subscripts. A convenient shorthand representation has evolved that is unequivocal, precise, and easily comprehended. In these structural diagrams, all of the carbon-to-carbon bonds of a compound are shown as straight line segments, either single, double, or triple. Carbon atoms are implied at all intersections of line segments, at their ends, and at all vertices. Hydrogen atoms bonded to carbon atoms are not shown, nor are carbon-to-hydrogen bonds; they are implied in such number that the carbon valence of four is filled. All other hydrogen atoms (e.g. in hydroxyl groups) are shown as H, and substituents on cyclic compounds are usually, but not necessarily, shown in full.
Thus CH3CH2CH2CH3 becomes simply
and CH3CCCH3 becomes .
Atoms other than carbon and hydrogen are always represented by their symbols. Examples are as follows:
| = | Chloroprene | = |
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| = | trans-2-Butene | = |
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| = | Ethylene oxide | = |
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| = | Neopentane | = |
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| = | n-Octane | = | |
More Cyclic Ethers
Returning now to our main stream of thought, further representative examples of cyclic ethers are shown below:
| Propylene oxide | | | Glycidol
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| Furan | | | Tetrahydrofuran (THF)
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| Pyran | | | Tetrahydropyran
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| Dioxane | | | 1,4-Dioxin
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| | 2,3,7,8-Tetrachlorodibenzodioxin (TCDD). This is the dioxin of pollution infamy.
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Ketones and Aldehydes
Compounds with two hydroxyl groups bonded to a single carbon atom are unstable in general. They split off a molecule of water spontaneously to form ketones or aldehydes with an oxygen atom double-bonded to carbon:
| The product is a ketone, often written RCOR'.
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| The product is an aldehyde, often written RCHO.
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Some common aldehydes are:
HCHO | Formaldehyde; methanal
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CH3CHO | Acetaldehyde; ethanal
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OHCCHO | Glyoxal; ethanedial
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CH3CH2CHO | Propionaldehyde; propanal
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CH2=CHCHO | Acrolein; propenal
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CH3(CH2)2CHO | Butyraldehyde; butanal
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CH3(CH2)3CHO | Valeraldehyde; pentanal
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(CH3)2CHCH2CHO |
Isovaleraldehyde; 3-methylbutanal
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CH3(CH2)4CHO | Caproaldehyde; hexanal
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| Furfural
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Some representative ketones are:
CH3COCH3 | Acetone; 2-propanone; 2-oxopropane; 2-ketopropane; dimethyl ketone |
ClCH2COCH3 | Chloroacetone
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CH3COCH2CH3 | Methyl ethyl ketone (MEK); 2-butanone; 2-oxobutane; 2-ketobutane
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CH3COCH=CH2 | Methyl vinyl ketone; 3-butenone
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CH3COCH2COCH3 | 2,4-Pentanedione
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| Camphor; 2-camphanone
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Review of Systematic Name Endings and Prefixes
The classes of compounds considered so far have the following systematic name endings:
-ane | = | Saturated aliphatic hydrocarbon
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-ene | = | Aliphatic hydrocarbon containing a double bond
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-yne | = | Aliphatic hydrocarbon containing a triple bond
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-enyne | = | Aliphatic hydrocarbon containing both a double and a triple bond
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-ol | = | Alcohol
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-one | = | Ketone
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-al | = | Aldehyde
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-yl | = | Radical or group
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-ylidene | = | Group disubstituted on a terminal carbon atom
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Some of the systematic name prefixes we have mentioned are:
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halo- | = | (Chloro-, bromo-, etc.) halogen-substituted
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poly- | = | Polymeric
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hydroxy- | = | HO-substituted
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alkoxy- | = | RO-substituted
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oxo- or keto- | = | Containing an oxygen atom double-bonded to a carbon atom that in turn is bonded to two other carbon atoms
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By now it must be abundantly clear that optional names exist for most organic compounds.
Readers are urged to e-mail questions, comments, or suggestions for further topics in the field of organic nomenclature to the author at: 74654.1335@compuserve.com.
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