1. The structure which has a five-membered ring like structure with two distorted hydrogen bonds is predicted to be the global minimum.

2. Compounds having five-membered heterocyclic rings include chlorophyll, hemoglobin, indigo, tryptophan, and certain polymers.

3. A five-membered heterocyclic ring compound, C4H5N, having an odor similar to chloroform. It is the parent compound of hemoglobin, chlorophyll, and many other complex, biologically active substances.

4. Tetronic acid, tetronic amine and their derivatives are five-membered heterocyclic compounds along with bio- and pharmacological activities.

5. The six-membered rings exhibit slightly distorted chair, extremely distorted chair and half-chair conformation respectively, and the five-membered ring exhibits an envelope conformation.

6. In the light of the interpretation of mass spectra of cyclic sulfoxides and the character of the strongest peak of PSO3E mass spectra, PSO3E were a series five-membered cyclic sulfoxides.

7. All transition states, activation energies and potential curves of four possible reaction paths were obtained. It was found that the homolysis of N—NO2 bond in five-membered ring is the initial step.

8. Proline is the only natural amino acid which contains an important five-membered ring as part of a secondary amino group.