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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	=
	=	trans-2-Butene	=
	=	Ethylene oxide	=
	=	Neopentane	=
	=	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
	Furan			Tetrahydrofuran (THF)
	Pyran			Tetrahydropyran
	Dioxane			1,4-Dioxin
			2,3,7,8-Tetrachlorodibenzodioxin (TCDD). This is the “dioxin” of pollution infamy.

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'.
	The product is an aldehyde, often written RCHO.

Some common aldehydes are:

HCHO	Formaldehyde; methanal
CH3CHO	Acetaldehyde; ethanal
OHCCHO	Glyoxal; ethanedial
CH3CH2CHO	Propionaldehyde; propanal
CH2=CHCHO	Acrolein; propenal
CH3(CH2)2CHO	Butyraldehyde; butanal
CH3(CH2)3CHO	Valeraldehyde; pentanal
(CH3)2CHCH2CHO	Isovaleraldehyde; 3-methylbutanal
CH3(CH2)4CHO	Caproaldehyde; hexanal
	Furfural

Some representative ketones are:

CH3COCH3	Acetone; 2-propanone; 2-oxopropane; 2-ketopropane; dimethyl ketone
ClCH2COCH3	Chloroacetone
CH3COCH2CH3	Methyl ethyl ketone (MEK); 2-butanone; 2-oxobutane; 2-ketobutane
CH3COCH=CH2	Methyl vinyl ketone; 3-butenone
CH3COCH2COCH3	2,4-Pentanedione
	Camphor; 2-camphanone

Review of Systematic Name Endings and Prefixes

The classes of compounds considered so far have the following systematic name endings:

-ane	=	Saturated aliphatic hydrocarbon
-ene	=	Aliphatic hydrocarbon containing a double bond
-yne	=	Aliphatic hydrocarbon containing a triple bond
-enyne	=	Aliphatic hydrocarbon containing both a double and a triple bond
-ol	=	Alcohol
-one	=	Ketone
-al	=	Aldehyde
-yl	=	Radical or group
-ylidene	=	Group disubstituted on a terminal carbon atom
Some of the systematic name prefixes we have mentioned are:
halo-	=	(Chloro-, bromo-, etc.) halogen-substituted
poly-	=	Polymeric
hydroxy-	=	HO-substituted
alkoxy-	=	RO-substituted
oxo- or keto-	=	Containing an oxygen atom double-bonded to a carbon atom that in turn is bonded to two other carbon atoms

 
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.