2- Monocyclic Compound

Aromatic species include the neutral molecules pyrrole, furan and thiophene (1 Z = NH, O, S) and the pyrrole anion (2). The radicals derived from these rings are named pyrryl, furyl and thienyl. The 2-furylmethyl radical is called furfuryl. Compounds in which two pyrrole nuclei are joined by a CH2 group are called dipyrromethanes when the linkage is by a CH group, they are named dipyrromethenes . The 2- (3) and 3-pyrrolenines (4) are isomeric with the pyrroles, but are nonaromatic as the ring conjugation is broken by an. s/r -hybridized carbon atom. 

Three types of cationic species exist (5-7) all are non-aromatic. The 2-oxo derivative exists in two tautomeric forms (8 and 9) the 3-oxo derivatives have a unique structure (10). 

Neutral aromatic Pyrrole species anion v Isomers of aromatic pyrroles  

Three types of dihydropyrrole (11-13) and two types of dihydro-furan and -thiophene exist (12-13), but only a single class of tetrahydro compounds (14). 

Reduced thiophenes and furans are named systematically as 2,3-dihydro (12), 2,5-dihydro (13) and 2,3,4,5-tetrahydro compounds (14). Alternatively, delta (A) can be used to indicate the position of the remaining double bond. Thus, (12) and (13) are named as A2- and A3-dihydro compounds, respectively tetrahydrothiophene is also called thiophane. 

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Nitration and aromatic reactivity C. The nitration of monocyclic compounds... 

If an open-chain organic molecule contains an electron acceptor and an electron donor site, two carbon atoms may be combined intramolecularly. This corresponds to the synthesis of a monocyclic compound. 

Nitration of monocyclic compounds is summarized in Table 4. Substitution occurs in the expected positions. The reaction conditions required are more vigorous than those needed for benzene, but less than those for pyridine. Ring nitration of oxazoles is rare, but (114) has been obtained in this way (74AHC(17)99). 

Tliese derivatives quite generally exist in the oxo or thioxo tautomeric forms. Monocyclic compounds are rare for instance, Lavergne et at reported that compound 58 exists as the thioxo tautomer 58a and not as the more antiaromatic mercapto tautomer 58b on the basis of the similarity of the NMR spectra of 58 with that of 59 (80RTC301). 

Tire final chapter, which will complete our survey of heteroaromatic tautomerism with a survey of monocyclic compounds with six-membered rings, will appear in a subsequent volume. 

This sesquiterpene is a monocyclic compound, first isolated from the essential oil of Bisabol myrrh by Tucholka. It was found in oil of limes, and described by Burgess under the name limene. It occurs in several other essential oils. When separated by fractional distillation from lemon oil, Gildemeister and Mullerfound it to have the following characters —... 

The Huckel rule is strictly applicable only to monocyclic compounds, but the genera] concept of aromaticity can be extended beyond simple monocyclic compounds to include polycyclic aromatic compounds. Naphthalene, with two... 

The retrosynthetic operations that we have addressed thus far have not resulted in significant structural simplification. After all, intermediate 6 still possesses a linear fusion of four rings and six contiguous asymmetric carbon atoms. But, nevertheless, intermediate 6 could potentially be derived in one step from intermediate 8, a polyunsaturated monocyclic compound containing only one stereogenic center. Under conditions that would be conducive to a heterolytic cleavage of the C-OH bond in 8, it is conceivable that the resultant tertiary allylic carbonium ion 7 would participate in a... 

In most cases there exists at elevated temperatures a mobile equilibrium with the monocyclic compound 4 dominating in the equilibrium mixture, whereas at room temperature the individual structures 3 and 4, respectively, are stable and can be isolated in pure form. 

The major structural difference between monocyclic and bicyclic compounds should be obvious camphene and camphor exhibit bridged structures. It should be noted, however, that the monocyclic compounds can be further distinguished from each other based on the position of the oxygen atom, located at C-2 in carvone, and at C-3 in pulegone, and in the menthones. Work by others had shown that the... 

Before the advent of the petrochemical industry carbocyclic aromatic compounds, such as naphthalene, phenol, and pyridine, provided the source of many important industrial chemicals including dyestuffs, while the monocyclic compounds continue to play an important role as fuels and starting materials. 

Monocyclic compounds with two amino functionalities like 1 were converted to the dinitriles 2 and subsequently reduced to the amines 3. An intramolecular... 

Various heterocyclic structures, among them 3-substituted-hexahydro-277-pyrimido[l,2- ]pyrimidin-2-ones 190, have been prepared by solid-phase synthesis. The acetates 187 were reacted with diaminoalkanes, the resulting diamines 188 cyclized with BrCN to the monocyclic compounds 189, which were cleaved and cyclized with Et3N to give 190 (Scheme 30) <2005TL5289>. 

In compounds with R=H, at equilibrium the proton completely exchanged to R = D. For 297 (R = Me) and 299 (R = Me) ring closures were slower and the equilibrium shifted more toward the monocyclic compounds (Equations 29 and 30) <20050BC1964>. 

A series of l/f-pyrrolo[2,l-r][l,4]oxazin-l-ones 196 are also the product of an LJgi multicomponent reaction between proline (and also other a-amino acids that gave the corresponding monocyclic compounds) and several isonitriles in the presence of commercially available glycolaldehyde dimer (Equation 3) <20010L4149>. 

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