There are more than 4000 Phenolic compounds. All are naturally-occurring in plants. Phenolics are formed from the essential amino acid phenylalinine (FEE-null-AL-uh-neen). Some phenols protect plants from UV radiation; others form pigmentation (the anthocyanins, in the flavanoid sub-group of Phenolics, impart colors); and yet others protect plants from diseases. The potential life-lengthener, resveratrol, which is rich in red grapes, is a current hero amidst the Phenols. A generic phenol molecule is shown at left. Those hexagons are benzene rings (don't worry--these are naturally-occurring chemicals comprised mostly of carbon).
In the human perception of wines, Phenolics are associated with wine color and tannins. If the winemaker presses and re-presses white grapes enthusiastically, the last bit of juice extracted from the skins and pulp is richer in Phenolic compounds. If used, this can result in overly-tannic wine (bitter!). In a red wine worthy of aging, it's not such a problem, because over time, the tannin molecules will chain up, which the palate perceives as "softer" tannins--a good thing. In white wines, the final pressings are best never even created--by the decade or so needed to smooth the wine out, the fruit will be gone.
Fewer than half the Phenolic compounds have been analyzed and understood, in case you or your kids are in search of a fascinating and wild frontier of scientific knowledge to explore. 140-year lifespans might be the payoff! How would you feel about having your first child at, say, 88 years old?