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

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

* β-Lactams fused to unsaturated five-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.

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.

Quinazoline is a compound made up of two fused six-membered simple aromatic rings, a benzene ring and a pyrimidine ring.

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.

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.

Gray arsenic ( α-As, space group Rm No. 166 ) adopts a double-layered structure consisting of many interlocked ruffled six-membered rings.

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

This commonly seen model of aromatic rings, namely the idea that benzene was formed from a six-membered carbon ring with alternating single and double bonds ( cyclohexatriene ), was developed by Kekulé ( see History section below ).

The prototypical structure consists of 4 six-membered rings and a furan ring.

These tetrahedrons together form a 3-dimensional network of six-membered carbon rings ( similar to cyclohexane ), in the chair conformation, allowing for zero bond angle strain.

The aromatization of six-membered rings by selenium is not clearly understood, but it does produce H < sub > 2 </ sub > Se.

Boratabenzenes have a negative charge on their six-membered rings and act as strong π-donating ligands like a cyclopentadienyl anion, which is often used in transition metal complexes.

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

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.

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.

This property is often utilized in molecular biochemistry for the purposes of modifying saccharide rings, as many five-and six-membered sugars often have vicinal diols.

Since all the six-membered rings in C </ sub > 80 </ sub >- I </ sub > h </ sub > are equal the two encapsulated Ce atoms exhibit a three-dimensional random motion.