Text book of chemistry for nurses and students of home economics by Macleod Annie Louise

Author:Macleod, Annie Louise. [from old catalog]
Language: eng
Format: epub
Tags: Chemistry
Publisher: New York [etc.] McGraw-Hill book company, inc.
Published: 1920-03-25T05:00:00+00:00

The strength of this attraction

is such that this carbon ring is perfectly stable, behaving in all respects like a saturated compound in spite of these apparently free valences.

The simple hydrocarbon, CeHe, with each carbon joined to one hydrogen atom, is called benzene, and the aromatic compounds may be looked upon as derived from this by replacement of one or more H's by other atoms or groups. For this reason the six-carbon ring is spoken of as the benzene ring or nucleus. The radicle CeHs, corresponding to the radicles CH3, C2H6, etc. is called the phenyl radicle. The higher hydrocarbons are formed by substituting alkyl groups for hydrogen in benzene, as for instance toluene, CeHe.CHa; xylene, C^^ (0113)2; ethylbenzene, C6H5.C2H6. The alkyl groups thus introduced are spoken of as side chains. There may be one or more side chains in the ring, and these may be of any length, according to the size of the group introduced, and may be saturated or unsaturated. Styrene, C6H6.CH:CH2, is an aromatic compound with an unsaturated side-chain.

It would be far beyond the scope of this book to deal with the aromatic compoimds in detail. A few general characteristics will be pointed out, but for further information a larger work must be consulted.

Aromatic compoimds exist which have the phenyl radicle combined with halogen to give halogen derivatives, with hydroxyl to give alcohols, with carbonyl to form

ketones and aldehydes, and with carboxyl to form acids, and these groups may be directly attached to the nucleus or may be separated from it by a longer or shorter chain of carbon atoms. While the properties of all these characteristic groups are somewhat modified by the benzene ring to which they are attached, they resemble the corresponding aliphatic compounds sufficiently in their general reactions so that no special attention need be given to them here. It may be taken as a general rule that side-chains and their substituent groups behave like aliphatic compounds, whereas the nucleus and any substituent introduced into the nucleus directly will show aromatic properties. This is particularly evident in the case of compounds containing hydroxyl, so much so that compounds with hydroxyl in the nucleus are classed together under the name of phenols, and only those with the hydroxyl in the side-chain of an aromatic nucleus are called aromatic alcohols. The phenols, while showing certain alcoholic characteristics, are so influenced by the presence of the benzene nucleus that they behave like weak acids, forming salts by replacement of the H of the OH with Na or K, e.g. CeHsONa, sodium phenolate. On account of this acid characteristic the first member of the series, phenol, was supposed, when first discovered, to be an acid, and was named carbolic add, a name which is still retained in general use although chemically incorrect. The phenols in general have antiseptic properties, and some of the higher members, as well as carbolic acid, are used as antiseptics, preservatives, and deodorants.

CHAPTER XVIII

Proteins and Vitamines

One of the most important, and one of the most complex, groups of substances with which the chemist has to deal is the group of proteins.

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