Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/569

Rh HYDROCARBONS.] CHEMISTRY 557 Methane. H H H Ethane, or C W* 5 or C TT H H H Propane, or ethyl-methane. They may likewise be formulated as hydrides of C B H 2n+1 radicles, in accordance with their formation from the haloid ethers of these radicles by the action of nascent hydrogen OH. = CHo.H ; CnEL. = C 9 Hr.H : CqH 8 = CoH 7 .H. 4 3 JO Z J J o O I Methane, h dilde Ethane. Ethyl hydride. Propane. Propyl hydride. More generally, the paraffins may be regarded as formed by the coalescence of any hydrocarbon radicles, furnishing by their addition the necessary number of carbon and hydrogen atoms ; thus CH 4 = CH 3 H = CH/.Hg = CH &quot;.H 3 Methane. Methyl hydride. Methene hydride. Methenyl hydride. Ethane. V,- -L-Lo. V^JLJLo Methyl methane, or dimethyl. CTT // TT p TT /// TT 24 *~^2 2&quot;^3 *~^3 Ethene hydride. Ethenyl hydride. = CBL.CA;,HK = CH 2 &quot;(CH 3 ) 2 or H Q C H { CH 3 CEL Methene dimethide, or dimethyl methane C 4 H 10 = C 2 H 5 .C 2 H 5 = CH 3 .C 3 H 7 = C 2 H 4 &quot;(CH 3 ) 2 = Butane, or Ethyl ethane, Propyl methane, or Ethene dimethide or tetrane. or diethyL methyl propane. dimethyl ethane. CH&quot;(CH 3 ) 3. Trimethyl methane, or methenyl trimethide (isotetrane). The number of possible methods of representing a paraffin thus greatly increases with the complexity of the molecule, but it must not be inferred from these formulae that the radicles represented as composing a paraffin molecule have a separate existence in the compound. Such formulation expresses simply the possible modes of formation by which the compound can be produced. For instance a. The ethyl hydride obtained by the action of nascent hydrogen upon ethyl iodide (C 2 H S I + H 2 = C 2 H 6 + HI) is identical with the ethene hydride produced by the action of nascent hydrogen on an ethene haloid ether (C 2 H 4 &quot;I 2 + 2H 2 = C 2 H 4 &quot;H 2 + 2HI), and with the dimethyl formed by heating CH 3 I with aanetal [2CH 3 I + Zn = (CH 3 ) a 4-ZnIgj. /3. The propane (propyl hydride) obtained by the action of nascent hydrogen on propyl iodide, &c. (C 3 H 7 I + H 2 = C 3 H 7 .H + HI), is identical with the ethyl-methyl produced by the action of a metal on a mixture of the iodides of methyl and ethyl (CH 3 I + C 2 H 5 I + Na, = CHg.C5jH s + 2NaI), or by the action of zinc-ethyl on methyl iodide [Zn(C 2 H 5 ) 2 + 2CH 3 I = 2CH 3. C 2 H 5 + ZnlJ. 7. Methane obtained by the action of nascent hydrogen on methyl iodide is identical with the methenyl hydride formed by the action of nascent hydrogen on chloroform (CH&quot; Clo + 3H 9 = CH &quot;. H, + 3HC1). Thus it must not be supposed that, because ethane may be written as dimethyl, ethane contains methyl. On treating ethane with chlorine, for example, we do not ob tain methyl chloride (CH 3 C1), but substitution products of ethane, C 2 H 5 C1, and similar relations obtain throughout the series. Turning to the graphic formulae made use of in illus trating the formation of homologous series by the continuous coalescence of carbon atoms with the consequent increase of atomicity (p. 552), it will be seen that the homologous series of C B H 2n+1 radicles can be regarded as derived from the first member, methyl, CH 3, by the continuous addition of methene, CH 2 &quot; ; and as the paraffins can be regarded as derived from the first member, methane, by the substitution of C B H 2B+1 radicles for hydrogen, we have the following constitutional f orrnulaa for the four first members : Methane... CH 4 Ethane ..... CH 3 .CH 3 Propane ...OH 3. C 2 H 5 = CH 3. CH 2. CH 3 Butane ..... CH S. C 3 H 7 = CH 3. CH 2. C 2 H 5 = CH 3. (CH 2 ) 2. CH 3 Thus, with the increase of the number of atoms in the molecule we have an increased number of hydrocarbon radicles coalescing to form the paraffin ; in other words, we have increased complexity of structure, and thus the possible modes of arrangement, or the possible number of isomerides (see p. 550), becomes greater as the number of atoms becomes greater. The three first members, as will be seen from the above formulae, can only be written in the manner shown, and no isomerides exist. The fourth member, butane or tetrane, as already shown, when treating of isomerism (p. 550), can be written in two ways, and two isomerides are known. Similarly there can be three pen- tanes, four hexanes, six heptanes, &c. It has been found by Schorlemmer that all the paraffins of which the constitution is known can be classified under four series, viz. : 1. Normal paraffins, in which no carbon atom is combined with more than two other carbon atoms. (See formulas above.) 2. Isoparaffins, in which one carbon atom is combined with three others. Typical formula : C M H 2 +1 3. Ncoparaffins (Odling), in winch one carbon atom is combined with four others. Typical formula : C,H 2 +1 C m H 2m+1 4. Mesoparaffins (Odling), containing the group [HC(CH 3 ) 2 ] twice. Typical formula : HC(CH 3 ) 2 HC(CH 3 ) 3 With regard to the general properties of a paraffin, as compared with those of its isomerides, it has been observed that the boiling-points and specific gravities of the normal compounds are higher than those of the isomers. With respect to chemical stability, the normal paraffins are more difficultly decomposable than their isomers. The following list contains the names, formulae, boiling- points, and specific gravities of the most important paraffins known at the present time : NORMAL PARAFFINS. Names. Formulas. Boiling-points Specific gravities. Methane CH 4 C/xijj. Orijj 0113. CHg. CIi3 CH 3 .(CH 2 ) 2 .CH 3 CH 3 .(CH 2 ) 3 .CH 3 CH 3 .(CH 2 ) 4. CH 3 CH 3 .(CH 2 ) 5 .CH 3 CH 3 .(CH 2 ) 6 .CH 3 CH 3 .(CH 2 ) 7 .CH 3 CH 3 .(CH 2 ) 8 .CH 3 CH 3 .(CH 2 ) 9 .CH 3 CH 3. (CH 2 ) 10 .CH 3 CH 3. (CH 2 ) U .CH 3 CH 3 .(CH 2 )j2-CH 3 CH 3 .(CH 2 ) 13 .CH 3 CH 3 .(CH 2 ) J4 .CH 3 &amp;gt; Gaseous. 1C. 37 -39 69 - 70 98 -99 123 -125 147- 148 166 -168 180 -184 202 216 -218 236 -240 258 -262 278 600atOC. 628 18 663 18 691 18 716 16 ? 728 13 739 13 765 16 774 17 792 20 i 825 16 Solid. Ethane Propane Tetrane Pentane Hexane Heptane Octane Nonane Decane Endecane ... . Dodecane... . Tridecane ... . Tetradecane Pentadecane Hexdecane.. .