酉 was originally a wine-jar pictograph and serves as the alcohol/fermentation radical. Aldehydes are oxidised alcohols, so the chemistry naming convention reuses 酉 for the whole -ol/-al/-one family. Compare 醇 ('alcohol'), 酮 ('ketone'), 酶 ('enzyme').
荃 gives the sound quán directly. Pure phonetic borrowing for the modern chemistry coinage; the grass meaning has no role. The same -uán phonetic appears in 全, 痊, 醛, all reading quán.
