Structure monocyclic

All of these effects can be accounted for by extensions of an additivity scheme, when special increments are attributed to monocyclic structures and the combination of two ring systems having one, two, or three atoms in common [23]. Combination of a table containing values for these ring fragments with an algorithm for the determination of the smallest set of smallest rings (SSSR) [24] (see also Section 2.5.1) allows such a procedure to be performed automatically. 

An acetyl group in the 2-position favors the monocyclic structure presumably because of the resonance stabilization.12 The same observation was made with oxepin-2,7-dicarbaldehyde, oxepin-2,7-dicarboxylic acid, and oxepin-2,7-dicarbonitrile.23 Substituents in the 4- and 5-positions of the oxepin such as methyl or methoxycarbonyl groups shift the equilibrium towards the epoxide.12 24 Low temperature 1H NMR studies on 7-ethyloxepin-2-carbonitrile and ethyl 7-ethyloxepin-2-carboxylate established a nonplanar boat geometry with a ring-inversion harrier of 6.5 kcal mol-1.25... 

Langeland and Werstuik <2003CJC525> used ab initio and AIM (atoms-in-molecules) methods to study the structures and reactivity of various phosphate ozonides. Activation energies of the bicyclic complexes (4-ethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]octane ozonide, l-phospha-2,6,7-trioxabicyclo[2.2.2]octane ozonide, and 1-phos-pha-2,8,9-trioxadamantane ozonide) were found to be significantly higher than the monocyclic structures studied. 

Some types of microorganisms, in particular Chromobacterium violaceum, which in the process of performing vital functions can synthesize specific beta-lactam antibiotics that have a monocyclic structure are called monobactams. Nocardicins, in particular nocardicin A, are examples of such monobactams. 

In this chapter, the structures and chemistries of 1,3-dioxins, 1,3-oxathiins, and 1,3-dithiins are described, including both their fully saturated forms (1, 7, and 13) as well as their benzo analogs (6, 11, 12, and 17). The formally fully unsaturated monocyclic structures (4, 9, 10, and 16) contain only one endocyclic double bond with further unsaturation being accomodated by exocyclic double bonds (2, 3, 5, 8, 14, and 15), for example, by the introduction of a carbonyl group. Well known and intensively studied are the Meldrum s acid derivatives 18 and 19. In addition, 1,3-dioxane, 1,3-oxathiane, and 1,3-dithiane moieties can be part of spiro structures as well as hi- and tricyclic analogs. And finally, both the structures and chemistries of the corresponding sulfoxides and sulfones are also reported. 

Scheme 16.8. Didehydrophenol (19) was the first derivative of 13 that could be isolated in an argon matrix at 8 K. Comparison of measured and calculated spectra supports the assignment to a monocyclic structure 19. Evidence for bicyclic isomer 22 was not found. In contrast to 19, derivative 23 can be photochemically converted into carbene 24. ...

Sulfur-rich binary P-S anions of the type [S2P(p-S )2PS2] form monocyclic structures with sulfide or disulfide bridging units ( = 1, 2) (11.39). Another type of cyclic P-S anion with the general formula [(PS2) ] is formed in the reaction of white phosphorus with polysulfides in a non-aqueous medium these anions have homocyclic structures with two exocyclic sulfur atoms attached to each phosphorus atom, e.g. [P4Ss] (11.40). ... 

For avoiding chance correlations, three series of hydrocarbons with wide structural variations were considered 37 alkanes, 36 polyalkylcyclohexanes and 48 monocyclic structures (the full results are reported elsewhere 93 a)). 

Several reviewers of the June 1950 version of this report suggested, in the interest of homogeneity, that (1) the bicyclic fundamental parent structures should be numbered so that a return to the monocyclic forms would not change that numbering (2) the actual or potential isopropyl group should always be attached to the No. 1 ring carbon in both the bicyclic structures and the menthane-type monocyclic structures. The American committees decided this was not feasible (see report proper). A summary of the specific proposals made by reviewers follows. 

The chemistry of polyselenides, polytellurides, and their metal complexes is very well established. Typical structures of polyselenide dianions are shown in Fig. 16.8.5. In these species, the Se-Se bond distances vary from 227 to 236 pm, and the bond angles from 103° to 110°. The tethered monocyclic structure of Se - in the complex Sr(15-C5)2(Se9) has a three-connected Se atom forming two long and one normal Se-Se bonds at 295, 247, and 231 pm (anticlockwise in Fig. 16.8.5, with the longest bond represented by a broken line). The other Se-Se bonds are in the range 227-39 pm. 

Only scant reference has been made to model studies on these types of compounds. Thus ab initio (STO-3G) and MNDO calculations on l,5-dithia-2,4,6,8-tetrazocine propound a preference for the lOrc-electron planar monocyclic structure (3) (X = H), and suggest that the bicyclic [l,2,5]thiadiazolo[3,4-c][l,2,5]thiadiazole-2,5-S(IV) (4), an 8n system with a transannular C—C bond could never be the stable structure for this molecule. Hence it is proposed the preparation of... 

Figure 3.2 Monoterpenes (C10H16). (A) Myreene, an acyclic monoterpene. (B) a-Pinene, a dicyclic structure. (C) d-Limonene, a monocyclic structure. Courtesy Spiring Enterprises Ltd.

This carbocation has to have a monocyclic structure and is the simplest potentially degenerate (CH) carbocation. It can either be a degenerate cyclopropenyl cation [339] rearranging as in (221) or a static aromatic 2 t-electron structure [340], i.e. the simplest aromatic system (222). The ion... 

Catenane synthesis can be also achieved by dynamic molecular association. Figure 3.27 shows an example of catenane preparation through the dynamic formation of a palladium (Pd) complex. Mixing the Pd complex with pyridine-type ligands in water induces the formation of both a monocyclic structure and an interlocked catenane. An equilibrium exists between these two structures, and the catenane structures are more favorable at higher concentrations. In the catenane structure, the benzene rings stack next to each other due to favorable... 

The first syntheses of mesoionic compounds included 1,2,4-triazoles and their oxa and thia analogues. The structure postulated at first as (20) was rejected on stereochemical grounds and on consideration of the large dipole moment, to be replaced by a charged monocyclic structure, defined as mesoionic and considerably extended to a great variety of theoretically and practically important examples (57QR15, 76ahc(19)3). 

G.W.J. Fleet and co-workers synthesized L-(+)-swainsonine and other more highly oxygenated monocyclic structures that exhibited inhibitory activity toward naringinase (L-rhamnosidase). In order to remove a c/s-vicinal diol moiety in the endgame of the synthesis, the Corey-Winter olefination was utilized. 

A heteromeric, as opposed to a homomeric, six-component solid-state assembly, of composition 2(thiodiglycolic acid) 4(isonicotinamde), has been described by Aakeroy et al. (Fig. 11).23 As in the case of 2(carboxylic acid) 2(amide), the central core was based on an amide dimer. The two diacids served as U-shaped units that forced two amide dimers to stack via hydrogen bonding to give the monocyclic structure. 

Bonchev, D., Mekenyan, O., von Knop, J. and Trinajstic, N. (1979) On characterization of monocyclic structures. Croat. Chem. Acta, 52, 361-367. 

NMR spectra show a massive peak at 8 = 4.8 ppm, characteristic of structure P9d. At 8 = 5.2 ppm, a slight signal indicates structure P9d. The P9b unit can become partially cyclized to give structure PSe- When the polymer is prepared at low temperature, its bromine index is about 54%, which corresponds to a monocyclized structure P9e. As the polymerization temperature increases, the intensity of the characteristic sig-... 

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