What is the main feature of a Geminal Diol?

A geminal diol is characterized specifically by having two hydroxyl (-OH) groups attached to the same carbon atom. This structural feature distinguishes geminal diols from other kinds of alcohols or diols, where hydroxyl groups are located on different carbon atoms.

In the context of organic chemistry, geminal diols typically arise from the hydration of carbonyl compounds such as aldehydes and ketones, where the carbonyl carbon becomes bonded to two hydroxyl groups, resulting in the diol. This characteristic can lead to notable chemical reactivity, as geminal diols can often be less stable than their carbonyl precursors and may further dehydrate to form carbonyl compounds again.

The other choices outline structures that do not match the definition of a geminal diol. Therefore, recognizing that geminal diols specifically involve both hydroxyl groups on a single carbon atom is crucial for understanding their properties and reactions in organic chemistry.