In organic nomenclature, what distinguishes a geminal diol from a vicinal diol?

In organic nomenclature, geminal diols are characterized by having two -OH groups attached to the same carbon atom. This structural configuration distinguishes geminal diols from vicinal diols, which have -OH groups located on adjacent carbon atoms, but not on the same carbon.

When considering stability, it is important to note that geminal diols typically exist in equilibrium with their carbonyl counterparts (aldehydes or ketones) and are generally less stable than vicinal diols. Vicinal diols, which have their hydroxyl groups on two different carbon atoms next to each other, can often be more stable due to the spatial distribution of the -OH groups, allowing for better molecular interactions compared to the more strained configuration found in geminal diols.

Thus, the defining feature of geminal diols is indeed that they contain two -OH groups on the same carbon, making this the correct distinction between geminal and vicinal diols.