Ring pucker is a technical term used in chemistry. In sugar chemistry, five-membered rings such as the furanose form of ribose are more flexible and have a greater tendency to pucker than six-membered rings such as the pyranose form of glucose. Whereas the six-membered ring adopts a stable chair or boat conformation (see conformational isomerism) enhancing the anomeric effect, five-membered ring pucker results in sugars and sugar analogs of the furanose form having a less pronounced anomeric effect.