* β-Lactams fused to saturated five-membered rings:

** β-Lactams fused to oxazolidine rings are named oxapenams or clavams.

* β-Lactams fused to unsaturated six-membered rings:

* β-Lactams not fused to any other ring are named monobactams.

* β-Lactams fused to thiazolidine rings are named penams.

* β-Lactams fused to 2, 3-dihydrothiazole rings are named penems.

* β-Lactams fused to 2, 3-dihydro-1H-pyrrole rings are named carbapenems.

* β-Lactams fused to 3, 6-dihydro-2H-1, 3-thiazine rings are named cephems.

* β-Lactams not fused to any other ring are named monobactams.

** β-Lactams containing thiazolidine rings are named penams.

** β-Lactams containing pyrrolidine rings are named carbapenams.

** β-Lactams containing 2, 3-dihydrothiazole rings are named penems.

** β-Lactams containing 2, 3-dihydro-1H-pyrrole rings are named carbapenems.

** β-Lactams containing 3, 6-dihydro-2H-1, 3-thiazine rings are named cephems.

** β-Lactams containing 1, 2, 3, 4-tetrahydropyridine rings are named carbacephems.

** β-Lactams containing 3, 6-dihydro-2H-1, 3-oxazine rings are named oxacephems.

For example, the nitrogen atom of all bicyclic β-lactams fused to five-membered rings is labelled position 4, as it is in penams, while in cephems, the nitrogen is position 5.

Metallic antimony adopts a layered structure ( space group Rm No. 166 ) in which layers consist of fused ruffled six-membered rings.

The nucleobases are classified into two types: the purines, A and G, being fused five-and six-membered heterocyclic compounds, and the pyrimidines, the six-membered rings C and T. A fifth pyrimidine nucleobase, uracil ( U ), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring.

Another large class of heterocycles are fused to benzene rings, which for pyridine, thiophene, pyrrole, and furan are quinoline, benzothiophene, indole, and benzofuran, respectively.

These molecules, composed primarily of fused rings of carbon ( either neutral or in an ionized state ), are said to be the most common class of carbon compound in the galaxy.

The core of steroids is composed of twenty carbon atoms bonded together that take the form of four fused rings: three cyclohexane rings ( designated as rings A, B, and C in the figure to the right ) and one cyclopentane ring ( the D ring ).

Polycyclic aromatic hydrocarbons are molecules containing two or more simple aromatic rings fused together by sharing two neighboring carbon atoms ( see also simple aromatic rings ).

Anthracene is a solid polycyclic aromatic hydrocarbon consisting of three fused benzene rings.

* Emil Erlenmeyer proposes that naphthalene has a structure of two fused benzene rings.

Phenanthrene is a polycyclic aromatic hydrocarbon composed of three fused benzene rings.

Pteridine is a chemical compound composed of fused pyrimidine and pyrazine rings.

Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings.

The dianion can also be considered as two fused cyclopentadienyl rings, and has been used as a ligand in organometallic chemistry to stabilise many types of mono-and bimetallic complexes, including those containing multiple metal-metal bonds, and anti-bimetallics with extremely high levels of electronic communication between the centers.

Naphthalene is the simplest such multi-ringed hydrocarbon, having the structure of two fused benzene rings.

Therefore, the study of heterocyclic chemistry focuses especially on unsaturated derivatives, and the preponderance of work and applications involves unstrained 5-and 6-membered rings.

The unsaturated rings can be classified according to the participation of the heteroatom in the pi-system.

They contain one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character.

Piperidines are resistant to an intramolecular Cope reaction but with pyrrolidine and with rings of size 7 and larger, the reaction product is an unsaturated hydroxyl amine.

Other methods for the direct formation of aromatic rings from substituted, unsaturated precursors include the Dötz reaction, palladium-catalyzed benzannulation of enynes with alkynes, and Lewis-acid-mediated cycloaddition of enynes with alkynes.

This leads to saturated five-membered ( in furanoses ) or six-membered ( in pyranoses ) heterocyclic rings containing one O as heteroatom.

( The lipophilic steroidal structure is the series of connected six-and five-membered rings at the right of the structure, while the three oxygen-rich sugar rings are at left and below.

In order to achieve the stable aromatic sextet in both rings, one electron from the seven-membered ring is transferred to the five-membered ring.

Simple monocyclic aromatic rings are usually five-membered rings like pyrrole or six-membered rings like pyridine.

Mordenite ’ s molecular structure is a framework containing chains of five-membered rings of linked silicate and aluminate tetrahedra ( four oxygen atoms arranged at the points of a triangular pyramid about a central silicon or aluminium atom ).

An Atrane is a tricyclic molecule with three five-membered rings.

In 2000, Robert R. Holmes and his co-workers reported a new class of silatranes that contain three six-membered rings and revealed that these atranes have weaker nitrogen donor interaction in comparison with corresponding ones bearing three five-membered rings.

Molecules with a high amount of ring strain consist of three, four, and some five-membered rings, including: cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, propellanes, propellanes, epoxides, aziridines, cyclopentenes, and norbornenes.

Glycals can be formed as pyranose ( six-membered ) or furanose ( five-membered ) rings, depending on the monosaccharide used as a starting material to synthesize the glycal.