Another distinct difference between digallic acid and leucodigallic acid
is the fact that the formaldehyde condensation product of the former
resembles gallic acid, whereas that of the latter resembles tannin; it
is therefore probable that the leucodigallic acid part of the tannin
molecule imparts this characteristic property to tannin.

---CO.O---
^ ^
| | | |
HO V OH COOH V OH
OH OH
[Illustration: Digallic Acid becomes...]

---CO.O---
^ ^ OH
| | | |
HO V OH COOH V OH
OH OH
[Illustration: Luteic Acid becomes...]

---CO.O---
^ ^ OH
| | | |
HO V --O.CO-- V OH
OH OH
[Illustration: Ellagic Acid becomes...]

COOH COOH
^ _______ ^