Robinson circle

When we say cycloheptatriene is not aromatic but cycloheptatrienyl cation is we are not comparing the stability of the two to each other Cycloheptatriene is a stable hydrocarbon but does not possess the special stability required to be called aromatic Cycloheptatrienyl cation although aromatic is still a carbocation and reasonably reac tive toward nucleophiles Its special stability does not imply a rock like passivity but rather a much greater ease of formation than expected on the basis of the Lewis struc ture drawn for it A number of observations indicate that cycloheptatrienyl cation is far more stable than most other carbocations To emphasize its aromatic nature chemists often write the structure of cycloheptatrienyl cation m the Robinson circle m a ring style... 

By this choice, the use of Robinson circles clearly indicates the aromatic, even if not truly double bond, character throughout the entire recticular [41] kernel of the molecule. The systemic canonical name for heme thus becomes ... 

The circle m a hexagon symbol was first suggested by the British chemist Sir Robert Robinson to represent what he called the aromatic sextet —the six delocalized TT electrons of the three double bonds Robinson s symbol is a convenient time saving shorthand device but Kekule type formulas are better for counting and keeping track of electrons especially m chemical reactions... 

Nowadays it is very difficult to pinpoint in the classical literatures in organic chemistry the credit of attributing the relative stability of unsaturated hydrocarbon molecules to K(G) [2, 3], On the other hand, long before these quantum-chemical theories were introduced Robinson proposed using a circle inside each benzene ring of an aromatic hydrocarbon molecule to represent the six mobile electrons and also the derived aromatic stability [4], However, his symbol does not reflect any difference in the stability between I and II as,... 

Figure 27(c)]. It remains to be noted that Borromean links composed of metric circles are impossible,108 that Borromean links composed of three triangles or three squares have inspired sculptures by John Robinson,109 and that this link, in the form of three interlocked triangles, was known to the ancient Scandinavians as Odin s triangle or the Walknot (meaning knot of the slain ).110... 

Figure 3 Normative olivine component in partial melt and mol.% enstatite component in cpx as a function of pressure along the fertile peridotite solidus, based on experimental data and pMELTS (sources pMELTS (solid circles, Ghiorso et ai, 2002), CMASN (open circles, Walter and Presnall, 1994), CMASE (open squares, Gudfinnsson and Presnall, 2000), and for natural experimental compositions (filled triangles, Canil, 1992 open diamonds, Robinson and Wood, 1998 filled diamonds, Robinson et aL, 1998 ...

Figure 37 presents data of Robinson for tungsten surfaces. The dashed lines represent the decay of the diffracted intensity predicted by Eq. (38) and clearly there are significant discrepancies with the experimental values (open circles). If a roughness factor is introduced (Robinson used a partial occupancy model), the data can be fit quite well (solid lines). 

Figure 37. Crystal truncation rods (CTRs) for W(IOO) in ultrahigh vacuum. Open circles, experimental data. Solid and dashed lines are, respectively, fits with and without consideration of surface roughness. Inset Reciprocal space diagram. (From Robinson, I. K., Phys. Rev. B. 33, 3830, 1966, with permission.)...

Fig. 89. Schematic representation of the 3-D framework in [Ag(L5i)]NO ), with circles representing Ag cations, filled bars representing L51 and empty bars representing Ag-Ag bonds. (From Scheme 1-D in Robinson, F. Zaworotko, M. J. Chem. Soc. Chem. Commun. 1995, 2413.)...

Fig. 6-6. Latitudinal distribution of acetylene open circles indicate aircraft data over the Pacific from Rasmussen (Robinson, 1978), and filled circles are data for surface air over the Atlantic from Ehhalt et al. (1986).

Fig. 10-2. Historic development of human-made global C02 and S02 emissions. Solid curve, data for C02 from Bolin et al. (1981) circles, data for S02 from Robinson and Robbins (1986b) squares, data from Cullis and Hirschler (1980).

Figure 263 is from a rare pamphlet distributed at an 1886 meeting of the German Chemical Society that celebrated Kekule s structure work. The monkeys adopt two rapidly alternating structures (tails entwined and not entwined). The modem representations for benzene [dotted or solid circle in the hexagon — see Figure 71(b)] were contributed by Johannes Thiele in 1899 and Sir Robert Robinson in 1925. ... 

Robinson J (2004) Squaring the circle Some thoughts on the idea of snstainable development... 

According to R. Robinson (1925), these experimentally obtained data are represented by the commonly used symbol 5, in which delocalized n-electrons are represented by a circle within a hexagon (Scheme 1.1). 

Armit/Robinson aromatic sextet inscribed circle notation ... 

Robinson had also proposed two ways to represent the structures with delocalized electrons. The first representation is the method of resonance structures which we already discussed in this book. By using this method, the benzene moleeule is represented by two resonance structures. The other representation proposed by Robinson describes the six delocalized k electrons by plotting a circle inside the six-membered ring. 

Fig. 8 Vapor-liquid equilibria of the mixture CO2 + C2H6. The upper figure shows a magnified view of the simulation results at 263.15 K by Vrabec et al. [41] with = 1 open circles) and = 0.954 (filled circles) compared with experimental data (plus signs) [260] and the Peng-Ro-binson equation of state with fc,y = 0 (dashed line) and kij = 0.132 (solid line). The figure at the bottom shows the simulation results by Vrabec et al. [41] for 223.15, 263.15, and 283.15 K with = 0.954 (filled circles) and the Peng-Robinson EOS with ky = 0.132 (solid line) compared with experimental data (plus signs) [260]...

Armit and Robinson introduced the notion of six-member rings in unsaturated compounds associated with the k electron aromatic sextet that bestows on them unusual stability, for which they have introduced the circle notation. Robinson later abandoned this novel model to characterize benzenoid compounds. It was Clar who not only adopted the notion of aromatic sextets, but significantly developed the model into a theory, which could explain several regularities of selected properties of these compounds. Clar s aromatic sextet theory assigns to individual benzenoid hydrocarbons novel structural formulas, which are obtained by following the rules summarized in Table 11.1. 

FIGURE 2.8 Acids in organic/aqueous solvents (1) 2-propanol 5%, (2) methanol 10%, (3) ethanol 10%, (4) 2-propanol 10%, (5) methanol 20%, (6) ethanol 20%, (7) glycerol 50%, (8)l,4-dioxane 15%. Common logarithm of K (S)/KjiW) versns the reciprocal of the relative permittivity of the mixed solvent Aeids are indieated by plotting symbols formic, triangle acetic, cross propanoic, circle butanoie, square water, filled circle. From Robinson and Stokes (1959) with permission of Dover PubUeations. 

---