Others were equally sure it was a four-membered ring fused to a five-membered ring, known as a beta lactam.    From Wordnik.com.  [The Nobel Prize in Chemistry 1964 - Perspectives] Reference

Some chemists were convinced the structure contained two five-membered rings connected by a single bond, known as a thiazolidine-oxazolone.    From Wordnik.com.  [The Nobel Prize in Chemistry 1964 - Perspectives] Reference

Mascal attributes the stability of the two ions to their rigid trefoil construction of five-membered rings.    From Wordnik.com.  [Chemical & Engineering News: Latest News] Reference

The basic framework of an N-heterocyclic carbene is a five-membered ring made of two nitrogen and three carbon atoms.    From Wordnik.com.  [innovations-report] Reference

An additional contact is established between the O3 hydroxyl oxygen of the five-membered ring and zinc, which is now in an overall T.    From Wordnik.com.  [PLoS ONE Alerts: New Articles] Reference

Penicillins are very similar, although they contain a five-membered ring in place of the six-membered ring present in the cephalosporin.    From Wordnik.com.  [Citizendium, the Citizens' Compendium - Recent changes [en]] Reference

Of the 20 naturally occuring amino acids, proline is the only one that has a cyclic side chain, forming a five-membered ring that includes the backbone nitrogen.    From Wordnik.com.  [WN.com - Articles related to 3D TVs new battleground for plasma, LCD display makers] Reference

A whole no doubt derives from the stereochemistry of the five-membered ring C-1.    From Wordnik.com.  [Nobel Lecture The X-Ray Analysis Of Complicated Molecules] Reference