The characteristic flavour and odour of wines and spirits is dependent on the proportion of higher alcohols, aldehydes and esters which may be produced.
By the action of dehydrating agents they are converted into aldehydes or ketones.
Taking as types hydrogen, hydrochloric acid, water and ammonia, he postulated that all organic compounds were referable to these four forms: the hydrogen type included hydrocarbons, aldehydes and ketones; the hydrochloric acid type, the chlorides, bromides and iodides; the water type, the alcohols, ethers, monobasic acids, acid anhydrides, and the analogous sulphur compounds; and the ammonia type, the amines, acid-amides, and the analogous phosphorus and arsenic compounds.
Compounds containing the group - CH: O are known as aldehydes (q.v.), while the group >C: O (sometimes termed the carbonyl or keto group) characterizes the ketones (q.v.).
Thio-aldehydes, thio-ketones and thio-acids also exist.