Mono cyclic Structures

The larger all-carbon molecules, Cn (n= 10-24), are predicted to have mono-cyclic structures (cyclo[/z]carbons), molecules with n— 14, 18, 22, being expected to be aromatic, with closed An + 2 electron shells.1,25,26,32 The smallest cyclocarbon for which a reasonable stability is predicted is cyclo[18]carbon, Ci8.366-368 Both in-plane and out-of-plane n systems are aromatic. In contrast, the larger molecules (n = 30-40), are very reactive, while more stable polycyclic structures predominate for higher values of n, culminating in fullerene structures for n > 60. 

Bonchev, D., Mekenyan, O., Knop, J.V. and Trinajstic, N. (1979b). On Characterization of Mono-cyclic Structures. Croat.Chem.Acta, 52,361-367. 

Whether the a- and /3-pinenes (XCIX and C) are converted into mono-cyclic structures in vivo is not known. H alainen (142) has shown that both compounds are converted to glucuronic acid conjugates of undetermined nature in the rabbit. These conjugates yielded the aromatic hydrocarbon cymene (Cl) on heating with dilute acids. 

Conversion of Aromatic Rings to Nonaromatic Cyclic Structures. On treatment with oxidants such as chlorine, hypochlorite anion, chlorine dioxide, oxygen, hydrogen peroxide, and peroxy acids, the aromatic nuclei in lignin typically ate converted to o- and -quinoid stmctures and oxinane derivatives of quinols. Because of thein relatively high reactivity, these stmctures often appear as transient intermediates rather than as end products. Further reactions of the intermediates lead to the formation of catechol, hydroquinone, and mono- and dicarboxyhc acids. 

As far as we are aware, abscisin II is the only known sesquiterpene possessing the carbon skeleton of structure A. All the other mono-cyclic sesquiterpenes are thought to arise by way of ion D (the example given is bisabolene) or E (the example given is elemol) (21). 

UV irradiation (A>320 nm) of matrix-isolated silabenzene [137a] led to the disappearance of its absorptions and the appearance of bands of other unstable molecules, which were assigned to Dewar silabenzene [138]. This assumption is reasonable because sp hybridization of the silicon atom is preferable to sp hybridization and favourable to the stability of [138]. Besides, according to calculations the energy differences between mono-cyclic [137a] and bicyclic [138] structures decrease from CeHe (314 kJ moP ) to silabenzene CsSiHe (125 kJ moP ). 

In order to assess structural influences on the catalytic performance of mono-cyclic PEG-modifled phosphites, the monocyclic phosphites 14a,c, 17a-e, and 19b,c were used in the rhodium-catalyzed hydroformylation of 1-octene (Scheme 6). The catalysts were prepared in situ by adding a solution of [Rh(acac)(CO)2] as a catalyst precursor in toluene to the phosphite ligands... 

Unlike hydrocarbon-based fuels like methane and gasoline, coal has never been subjected to a comprehensive mechanistic analysis, due to the complexity of its molecular structure. However, coal s complex structure consists of various mono-cyclic units that can be explored aromatic hydrocarbons and heteroaromatic rings are recurring units in coal s structure, even while the overall structure varies geographically. Understanding low- and high-temperature oxidation reactions for these subunits and their reactive radical intermediates will facilitate a better understanding of their chemistry in combustion. 

Bifunctional oligobutadienes were found to contain, besides bifunctional molecules, non- and monofunctional molecules 16 l7,19), and from a series of polyesters and thiokols fractions of non-functional molecules of cyclic structure were isolated39,45) poly(oxypropylene) with target functionality f 3 contained fractions of mono- and bifunctional macromolecules 26,27,29 34), etc. 

Various bimolecular assemblies that have been proposed for the transition state are shown in Scheme 13 (14, 19a, 20g). Bicyclic transition state A involves transfer of bridging alkyl group (R) to the terminally located aldehyde, while transition structure B involves reaction between terminal R and bridging aldehyde. The reaction may proceed via mono-cyclic, boat-like six-membered transition state C. Transition structures of types B and C were originally proposed for the reactions of orga-noaluminum compounds and carbonyl substrates (26, 27). Ab initio calculations suggest that methyllithium dimer reacts with formaldehyde through a bicyclic transition state related to A (28). The dinuclear Zn... 

The official ACS report is limited to the naming of the simple acyclic, mono-cyclic, and bicyclic terpene hydrocarbons because official action has been taken only on the recommendations relating to these three classes of terpenes The term terpene hydrocarbons is intended to include not only the numerous C1QH16 hydrocarbons but also their hydrogenated derivatives and other hydrocarbons possessing similar fundamental structures they may be of natural or synthetic origin. 

Historically, the cyclic structure of benzene with symmetry, as shown in Fig. 7.3.15, was deduced by enumerating the derivatives formed in the mono-, di-, tri-substitution reactions of benzene. The structure can also be established directly using physical methods such as X-ray and neutron diffraction, NMR, and vibrational spectroscopy. We now discuss the infrared and Raman spectral data of benzene. 

The mono-cyclic ter penes j as the name indicates, have the structure of a single cycle or ring of hydrogen-carbon groups. 

C5H8, and may be either acyclic or cyclic with one or more benzenoid groups. They are classified as mono-cyclic (dipentene), dicyclic (pinene), or acyclic (myr-cene), according to the molecular structure. Many terpenes exhibit optical activity. Terpene derivatives (camphor, menthol, terpineol, bomeol, geraniol, etc.) are called terpenoids many are alcohols. 

In this chapter, keeping in mind the generation, characterization, and reactions of the cyclic polyynes, the interplay of organic chemistry and carbon cluster science during the last decade is presented. First, following short historical remarks (Section 6.2.1), recent research activity on the production of cyclo[ ]carbons from well-defined organic precursors is surveyed (Section 6.2.2). Second, major structural and electronic properties of mono-cyclic carbon clusters are presented in the context of theoretical considerations (Section 6.2.3), followed by observational results of photoelectron spectroscopy (Section 6.2.4). Third, considerations on the infrared activity of cyclic Cio will be presented (Section 6.2.5). Finally, this chapter ends with experimental as well as theoretical proposals for the structures of multicyclic polyynes (Section 6.3) and their relevance to the formation of fullerenes, in particular from polycyclic polyynes (Section 6.4). 

---