5. CH(OH)2C(OH3), from the tendency of all the preceding, corresponds with glyoxylic acid, an aldehyde acid, CHOCO(OH), because the group CO(OH), or carboxyl, enters into the compositions of organic acids, and the group CHO defines the aldehyde function.
6. C(OH)3C(OH)3 through the loss of 2H2O yields the bibasic oxalic acid CO(OH)CO(OH), which generally crystallises with 2H2O, following thus the normal type of hydration characteristic of ethane.[2]
Thus, by applying the principle of substitution, we can, in the simplest manner, derive not only every kind of hydrocarbon compound, such as the alcohols, the aldehyde-alcohols, aldehydes, alcohol-acids, and the acids, but also combinations analogous to hydrated crystals which usually are disregarded.
But even those unsaturated substances, of which ethylene, CH2CH2, and acetylene, CHCH, are types, may be evolved with equal simplicity. With respect to the phenomena of isomerism, there are many possibilities among the hydrocarbon compounds containing two atoms of carbon, and without going into details it will be sufficient to indicate that the following formulæ, though not identical, will be isomeric substantially among themselves:—CH3CHX2 and CH2XCH2X, although both contain C2H4X2; or CH2CX2 and CHXCHX, although both contain C2H2X2, if by X we indicate chlorine or generally an element capable of replacing one atom of hydrogen, or capable of uniting with it. To isomerism of this kind belongs the case of aldehyde and the oxide of ethylene, to which we have already referred, because both have the composition C2H4O.
What I have said appears to me sufficient to show that the principle of substitution adequately explains the composition, the isomerism, and all the diversity of combination of the hydrocarbons, and I shall limit the further development of these views to preparing a complete list of every possible hydrocarbon compound containing three atoms of carbon in the molecule. There are eight in all, of which only five are known at present.[3]
Among those possible for C3H6 there should be two isomerides, propylene and trimethylene, and they are both already known. For C3H4 there should be three isomerides: allylene and allene are known, but the third has not yet been discovered; and for C3H2 there should be two isomerides, though neither of them is known as yet. Their composition and structure are easily deduced from ethane, ethylene, and acetylene, by methylation, by methylenation, by acetylenation and by carbonation.
1. C3H8 = CH3CH2CH3 out of CH3CH3 by methylation. This hydrocarbon is named propane.
2. C3H6 = CH3CHCH2 out of CH3CH3 by methylenation. This substance is propylene.
3. C3H6 = CH2CH2CH2 out of CH3CH3 by methylenation. This substance is trimethylene.
4. C3H4 = CH3CCH out of CH3CH3 by acetylenation or from CHCH by methylation. This hydrocarbon is named allylene.