IDENTIFICATION BY PRESENCE OR ABSENCE OF HYDROXYL.
No other arrangement is possible keeping the valencies mentioned. Which formula, there fore, represents ethyl alcohol, and which the methyl ether If both compounds are treated with metallic sodium it is found to react only with the alcohol, hydrogen being evolved, and its place taken by sodium. Now in nearly all cases sodium reacts in this manner with all compounds containing the group — OH, hydroxyl. A compound known as phosphorus penta-chloride is a very good reagent for ascer taining the presence of hydroxyl. It has been found that if a compound contains —OH, this group is replaced by one chlorine atom when treated with the phosphorus penta-chloride. If it is allowed to act upon ethyl alcohol it produces a substance which on analysis is found to have the formula If this new body is compared with ethyl alcohol it will readily be seen that —OH has been replaced by one atom of chlorine. Con
sequently this reaction, and that of the sodium, shows that the alcohol contains a hydroxyl group. if the methyl ether is treated with phosphorus penta-chloride a far deeper change takes place, and the molecule is completely broken down. On inspecting the two con stitutional formula: previously deduced it will be seen that only No. contains a hydroxyl group. Consequently this must be the con stitutional formula for the alcohol, and the other formula, No. 2, that of the methyl ether. These two formula are completely in harmony with the chemical properties of the two sub stances. Instead of writing out the constitu tional formula fully it is slightly contracted. Thus :—