Linear allene

Scheme 18.8 Linear allenes isolated from seed oils.

A number of closely related linear allenes have also been isolated from seed oils (Scheme 18.8). Examples are laballenic acid (18) [27], lamenallenic acid (19) [28] and phlomic acid (20) [29]. The hydroxy acid 21 was isolated as part of a triglyceride from the Chinese tallow tree Sapium sebiferum [30] and as its methyl ester 22 from the related species Sapium japonicum [31], which is found in Japan. 

The potential carbodicarbene C(C(NMe2)2 2 has been known for a long time but no complex has been reported [101, 102]. It adopts a linear allene geometry in the free state but according to theoretical analysis exhibits a strong nucleophilic central carbon atom [4, 97] and can be seen as an allene with a hidden divalent carbon(O) character emerging in the presence of electron deficient electrophiles. Based on these findings a new field of chemistry will be opened and the number of compounds with a coordination mode should increase in the future. 

Similar data have been obtained for the adsorption of but-l-ene and isobutene on copper(i) and copper(ii) oxides. Although the results are less clear cut than with the propene system, in general a similar pattern emerges. The reversibly adsorbed species has infrared bands characteristic of a 7r-bonded allyl species. Addition of oxygen to reversibly adsorbed but-l-ene at room temperature results in bonds characteristic of acrolein and acetaldehyde. Methyl vinyl ketone is only formed at higher temperatures. The adsorption of the major partial oxidation products on copper(i) oxide was also investigated. Metha-crolein behaves like acrolein and is reversibly adsorbed. Methyl vinyl ketone, however, mainly forms carboxylate and carbonate types of structures. This reflects the ease of oxidation of the partial oxidation product. The reason for the higher selectivities observed with the branched alkenes can thus be ascribed to the relative ease of oxidation of the partial oxidation product from the linear allene. 

Using a multiple linear regression computer program, a set of substituent parameters was calculated for a number of the most commonly occurring groups. The calculated substituent effects allow a prediction of the chemical shifts of the exterior and central carbon atoms of the allene with standard deviations of l.Sand 2.3 ppm, respectively Although most compounds were measured as neat liquids, for a number of compounds duplicatel measurements were obtained in various solvents. 

Because of the linear geometry required of cumulated dienes cyclic allenes like cycloalkynes are strained unless the rings are fairly large 1 2 Cyclononadiene is the smallest cyclic allene that is sufficiently stable to be isolated and stored conveniently... 

Linear elastic models for rafting are reviewed in J. C. Chang, S. M. Allen. J... 

Malrieu predicted qualitatively that the l-silaallene framework would be nonlinear. but how much the moiety would deviate from 180 was unclear. The first quantitative values were seen with the isolation and structural determination of the two 1-silaallenes 56 and 59a, whieh have very similar Si=C=C angles of 173.5 and 172.0, respectively (Table III). This is an average deviation of 7.3 from linearity—significant, but relatively small compared to the deviations shown by the germanium and tin substituted allenes. 

An interesting carbene, 1-oxobutatrienylidene [25], having cumulated double bonds, has been found by IR spectroscopy in the photolysis (A>230nm) products of matrix-isolated l,2,3,4-pentatetraene-l,5-dione [26] (Maier et al., 1988) (in its turn the unstable dione [26] was generated by thermo- or photo-destruction of compound [27]). The second product was carbon monoxide. The linear structure of the carbene [25] has been suggested on the basis of two intense IR bands at 2222 cm and 1923 cm indicating respectively ketene and allene fragments. 

In 2009, Ritter and coworkers reported a selective Fe-catalyzed hydroboration of 1,3-dienes to produce linear ( )-y-disubstituted allylboranes under mild conditions when a combination of Ll-FeCl2 and magnesium metal as a catalyst was used. Tbe branched ( )-allylboranes were obtained by using L2-FeCl2 instead of Ll-FeCl2 (Scheme 26) [88]. For the synthesis of 2-borylallylsilanes, this method was superior to the previously reported silaboration of allenes [89]. 

This study, like that of Fisher and Allen (1993), incorporated a linear multistage model. However, the mechanism of trichloroethylene carcinogenicity appears to be non-genotoxic, and a non-linear model (as opposed to the linearized multistage model) has been proposed for use along with PBPK modeling for cancer risk assessment. The use of this non-linear model has resulted in a 100-fold increase in the virtually safe lifetime exposure estimates (Clewell et al. 1995). 

Fig. 15 The experimental geometries of allene- -HC1 and allene- -C1F, drawn to scale. The n-electron model for allene is also shown. The angles 2- - H and 2- - Cl, respectively, where is the centre of the C C bond, are both close to 90°, as required by rule 2. The hydrogen and halogen bonds both show small non-linearities. See Fig. 1 for key to the colour coding of atoms... 

Examples of the application of linear programming in chemical process plant design and operation are given by Allen (1971), Rudd and Watson (1968), Stoecker (1991), and Urbaniec (1986). 

ALLEN, D. H. (1971) Brit. Chem. Eng. 16, 685. Linear programming models. 

Box, K., Bevan, C., Comer, J., Hill, A., Allen, R., Reynolds, D., High throughput measurement of pKa values in a mixed-buffer linear pH gradient system. Anal. Chem. In press. 

In all liquids, the free-ion yield increases with the external electric field E. An important feature of the Onsager (1938) theory is that the slope-to-intercept ratio (S/I) of the linear increase of free-ion yield with the field at small values of E is given by e3/2efeB2T2, where is the dielectric constant of the medium, T is its absolute temperature, and e is the magnitude of electronic charge. Remarkably S/I is independent of the electron thermalization distance distribution or other features of electron dynamics in fact, it is free of adjustable parameters. The theoretical value of S/I can be calculated accurately with a known value of the dielectric constant it has been well verified experimentally in a number of liquids, some at different temperatures (Hummel and Allen, 1967 Dodelet et al, 1972 Terlecki and Fiutak, 1972). 

Ec in cyclopentane is estimated from the A value obtained by fitting the temperature dependence of mobility by a generalized Bagley equation (see Sect. 10.2). Schmidt and Allen (1970) found drift velocity in this liquid to be linear with field up to at least 62 KV/cm. 

Allen (106) also studied cobalt hydroformylation with a polymer-bound catalyst. The polymer was formed from diphenyl-p-styrylphosphine cross-linked with divinylbenzene. 2-Hexene was the substrate, and reaction conditions were 175°C and 1500-3000 psi of 1/1 H2/CO. The product aldehyde was 55% linear, and the effluent product solution contained 20-50 ppm cobalt. 

---