Note 48 — Chapter VIII · CARBON AND THE HYDROCARBONS

The homologues of ethylene, CnH2n, are also capable of direct combination with halogens, &c., but with various degrees of facility. The composition of these homologues can be expressed thus: (CH3)_x(CH2)y(CH)zCr, where the sum of x + z is always an even number, and the sum of x + z + r is equal to half the sum of 3x + z, whence z + 2r = x; by this means the possible isomerides are determined. For example, for butylenes, C4H8, (CH3)2(CH)2, (CH3)2(CH2)C, (CH2)(CH2)2CH, and (CH2)4 are possible.