four-membered

Others were equally sure it was a four-membered ring fused to a five-membered ring, known as a beta lactam.

The Nobel Prize in Chemistry 1964 - Perspectives 1964

The double door frame projects pilaster-like, with a four-membered cornice above, from which rises an elliptical arch, with an elliptical cornice about a foot above.

The Old Franciscan Missions Of California George Wharton James 1890

OXE has an unstable chemical structure (a four-membered ring containing three carbons and one oxygen) that makes it prone to being split open.

Ars Technica 2009

Here it is easy to see the chemical structure, a four-membered ß-lactam ring attached to a six-membered sulphur-containing ring -- derived most probably like the corresponding penicillin, from "� - (a-aminoadipoyl) - cysteinyl valine but in an oxidized form.

Nobel Lecture The X-Ray Analysis Of Complicated Molecules 1964