the Paraffins and their Derivatives. 209 



however, must not be taken to imply that in the normal paraf- 

 fins one proportion of methyl stands in a different relation to 

 the other proportion, or any one proportion of methylene in a 

 different relation to the remaining proportions. 



By the direct or indirect replacement in any paraffin, of one 

 proportion of hydrogen by a proportion of chlorine or other 

 radical, simple or compound, a great variety of mono-deriva- 

 tives of each of the several paraffins is obtainable. Represent- 

 ing the proportion of radical introduced in the place of one 

 proportion of hydrogen by the letter X, the mono-derivatives 

 of propane, for instance, will be expressible by the formula 

 C 3 H 7 X, those of butane and isobutane by the formulae 

 C 4 H 9 X and C 4 HJX respectively ; those of pentane, isopen- 

 tane, and neopentane by the formulas C 5 H n X, C 5 HnX, and 

 C 5 HnX respectively, and so forth ; the residues C 3 H 7 , C 4 H 9 , 

 C 4 HJ, C 5 H n , C 5 Hn, 5 Hn, &c. constituting the paraffin- 

 or alcohol- monad radicals propyl, butyl, isobutyl, pentyl, iso- 

 pentyl or ainyl, and neopentyl, &c. 



But it is found that in any single paraffin, the replacement 

 of one proportion of hydrogen by one proportion of some par- 

 ticular radical — chlorine, CI, or hydroxy!, OH, for instance — 

 gives rise to the production of at least two distinct isomers. 

 And a study of the formative and transformative reactions 

 of these isomers leads to the conclusion that the difference be- 

 tween them depends upon whether they result from a substi- 

 tution of the introduced radical for the hydrogen of a methyl or of 



a methylene residue (in butane for instance, H 2 Ck qtj 2 3 )y 



or for the hydrogen of a methyl or of a formyl residue (in iso- 

 butane for instance, HC (CH 3 ) 3 ). 



The paraffin radicals resulting in this way from the intro- 

 duction of a foreign radical in the place of the hydrogen of a 

 methyl- or of a methylen- or of a formyl- residue in the original 

 paraffin, are spoken of as primary, secondary, and tertiary 

 radicals respectively. To the root-names of the secondary and 

 tertiary radicals, moreover, it is convenient to add some di- 

 stinctive prefix ; and the prefix " iso " has been very generally 

 made use of, not only in the case of the primary radicals of 

 isoparaffins, but also in the case of the secondary and tertiary 

 radicals generally, though necessarily with much resulting 

 confusion. Occasionally, however, the prefix " pseudo " has 

 been applied in the case of the secondary radicals — a practice 

 it seems desirable to employ more systematically ; and, taking 

 the Greek letter ir for the index (-vfr being reserved for the 

 rarer case of the secondary radicals of the isoparaffins), the 



Phil. Mag. S. 5. Vol. 1. No. 3. March 1876. Q 



