. Biological stains, a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy). **; When the compound is complex it is customary to number the corners of the ring thus: In naming a compound in this way, the number of the corner to which a group is attached is given immediately before the name of the group. Thus, the three compounds shown above may be called respectively: 1, 2-dichlorobenzene, 1, 3-dichlorobenzene and 1, 4-dichlorobenzene. There is another type of substitution in the benzene ring which is very important in dye
. Biological stains, a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy). **; When the compound is complex it is customary to number the corners of the ring thus: In naming a compound in this way, the number of the corner to which a group is attached is given immediately before the name of the group. Thus, the three compounds shown above may be called respectively: 1, 2-dichlorobenzene, 1, 3-dichlorobenzene and 1, 4-dichlorobenzene. There is another type of substitution in the benzene ring which is very important in dye chemistry. Two atoms or groups having two valency bonds instead of one may also replace two hydrogen atoms, provided the replacement takes place simultaneously and the hydrogen atoms replaced are situated either in the ortho or in the para position to each other. Thus two oxygen atoms (which are bivalent) may replace two hydrogen atoms (which are mono- valent) forming the compound known as quinone CeHA, the formula for which is or as commonly written 0 M C C U I c C 0. In printed formulae, such as those that follow in this book, the quinone ring is often abreviated still further by omitting the double bonds within the ring. The substituent atoms or groups may or may not be alike, so long as both have two valency bonds entering into the combination. This type of substitution involves a rear- ranging of the double valency bonds in the benzene ring; and in compounds of this type, called quinoid compounds, the double bonds are supposed to be fixed, not mobile as in benzene. This change of the valency bonds takes place very readily in many dyes, and certain peculiarities of their behavior are explained by it; (see for example p. 84). Three mono-substitution products of benzene are of importance in considering the structure of dyes, namely; toluene or methyl- 13. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability
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