Extended carbon

The different forms of carbynes were assumed to be polytypes with different numbers of carbon atoms in the chains lying parallel to the hexagonal axis and different packing arrangements of the chains within the crystallite. Heimaim et al [23] proposed that the sizes of the unit cells were determined by the spacing between kinks in extended carbon chains, Fig. 3A. They were able to correlate the Cg value for the different carbyne forms with assumed numbers of carbon atoms, n (in the range n = 6 to 12), in the linear parts of the chains. 

For reviews of the addition of organometallic compounds to carbonyl groups, see Eicher, T. in Patai, Ref. 2, p. 621 Kharasch, M.S. Reinmuth, O. Grignard Reactions of Nonmetallic Substances, Prentice-Hall Englewood Cliffs, NJ, 1954, p. 138. For a review of reagents that extend carbon chains by three carbons, with some functionality at the new terminus, see Stowell, J.C. Chem. Rev., 1984, 84, 409. 

Given the interest in extended carbon systems in recent years, it seemed useful to study the solubility of C60 (fullerene) in various organic liquids.54 55 It was now for the solvents that the molecular surface properties were computed. The resulting Eq. (14) shows that, for this large nonpolar solute, solubility is enhanced by solvent molecule surface area and by the latter having somewhat... 

The 62-e diyne complexes 115 and 116 are effective scaffolds for the trimeriza-tion of the diynes and codimerization of diyne and alkynes, resulting in extended carbon chains coordinated to the cluster. Thus, reactions with R C=CC=CR (R = Ph, Me) afforded Ru4(M4-PPh) /i4-RCC(CsCR )CPhC-p -CCPhCRC (C=CR ) (CO)s (118 R = Ph, Me). The former was also found as a minor product from Ru4(/i4-PPh)(CO)i3 and PhC=CC=CPh. " These are 64-e clusters containing a /44-PPh ligand capping an RU4 face, together with a C12 ligand formed from... 

A further aspect of this chemistry is in relation to the preparation of extended carbon networks and related systems. Imaginative consideration of various as yet... 

Computational efforts to describe the conformational preferences of (R,R)-tartaric acid and its derivatives - mainly for isolated molecules - were made recently [18-25]. The conformations of these molecules also attracted attention from experimental chemists [22-40]. (/ ,/ [-tartaric acid and its dimethyl diester were observed in crystals, in conformations with extended carbon chain and planar a-hydroxy-carboxylic moieties (T.v.v and Tas for the acid and the ester, respectively) [25-28] (see Figure 2). The predominance ofthe T-structure was also shown by studies of optical rotation [31], vibrational circular dichroism (VCD) [23], Raman optical activity [32, 35], and nuclear magnetic resonance (NMR) [22, 33, 34]. The results of ab-initio and semiempirical calculations indicated that for the isolated molecules the Tsv and T as conformers were those of lowest energy [22, 21, 23, 25]. It should be noted, however, that early interpretations of NMR and VCD studies indicated that for the dimethyl diester of (/ ,/ [-tartaric acid the G+ conformation is favored [36-38]. 

Conformations of primary, secondary, and tertiary amides of (R,R)-tartaric acid, both symmetrically and asymmetrically substituted, have been studied ciys-tallographically [22, 24, 29, 30-40] Moreover, ab initio studies up to MP2 / 6-31G //RHF/6-31G level [41] for both the diamide and N,N,N ,N -tctramcthyl-diamide of (/ ,/ [-tartaric acid have been carried out [20, 22]. X-ray results have shown that primary and secondary amides of (R,R [-tartaric acid tend to adopt a conformation with the extended carbon chain - the Taa structure. In this Taa conformation both the a-hydroxy-amide moieties form planes and the structure gains stabilization from hydrogen bonding between donors, the NH, and acceptors, the proximal OH groups. Moreover, the Taa structure is favorably stabilized by the attraction of antiparallel local dipoles formed along distal C H and Csp2=0 bonds [18, 21, 22],... 

There is yet a small class of oxides, the neutral oxides, which do not belong to any of the classes before named they do not combine with water to form acids, nor do they neutralise acids. This class has tended steadily to decrease as chemical knowledge has extended. Carbon monoxide, nitrous oxide, and nitric oxide were once mcluded m this class, but each of these can be obtained by the loss of the elements... 

Fig. 3. Extended carbon networks containing diyne fragments linked by (a) sp3 carbons, (b) sp2 carbons, and (c) [3]-radialenes.

Fig. 5. An extended carbon network stabilized by Fe(CO)3 groups coordinated to cyclobutadiene fragments.

Aminoindolanes of the current invention having extended carbon chain lengthts at the 2 position were also prepared by the author as illustrated in Eq. 1 ... 

The incorporation of a phenyl ring as part of an extended carbon tether [(C) , n — 2] requires the preparation of the homologous [2-[(E)-phenyl-diazenyl]phenyl]acetic acid 89 or its methyl ester 90 (Scheme 22), which in a subsequent step has to be transformed into l-diazo-3-[2-[(E)-phenyldia-zenyl]phenyl]acetone. 

CBM-EX The Stanford University s extended carbon bond mechanism... 

This chapter examines the biosynthesis of three important components of biological membranes—phospholipids, sphingolipids, and cholesterol (Chapter 12). Triacylglycerols also are considered here because the pathway for their synthesis overlaps that of phospholipids. Cholesterol is of interest both as a membrane component and as a precursor of many signal molecules, including the steroid hormones progesterone, testosterone, estrogen, and cortisol. The biosynthesis of cholesterol exemplifies a fundamental mechanism for the assembly of extended carbon skeletons from five-carbon units. 

P Carotene, which is the precursor of retinal, the chromophore in all known visual pigments (Section 32.3.2). These examples illustrate the fundamental role of isopentenyl pyrophosphate in the assembly of extended carbon skeletons of biomolecules. It is evident that isoprenoids are ubiquitous in nature and have diverse significant roles, including the enhancement of the sensuality of life. 

The UV absorption spectra of simple enamines as well as those with extended carbon-carbon Tr-con-jugation are quite broad. A correlation with photoelectron spectra has also been made. ... 

A stereoregular polymer with all substituents on the same side of the extended carbon chain... 

The consecutive addition of alkyl halide to activated olefins by photoelectrocatalysis (PEC) of hydroxocobalamin hydrochloride allows the construction of extended carbon chains as shown for the synthesis of pheromone queen substance 9. The mild conditions of the B12/PEC reaction are suited for the addition of primary alkyl halides 10 containing a potential leaving group. This is illustrated in the synthesis of endo- and exo-brevicomin (11) (Scheme 4). 

Polymers formed from monosubstituted ethylenes can exist in three configurations isotactic, syndiotactic, and atactic. An isotactic polymer has all of its substituents on the same side of the fully extended carbon chain. (Iso and taxis are Greek for the same and order, respectively.) In a syndiotactic polymer (syndic means alternating ), the substituents regularly alternate on both sides of the carbon chain. The substituents in an atactic polymer are randomly oriented. 

Since tetraethynylethenes represent a repeat unit in more than one two-dimensional carbon network including 45 and 46 (Fig. 13-1) [1] the preparation of a specific network cannot be accomplished by simple oxidative polymerization of 20, but rather requires a more characteristic macrocydic precursor as starting material. Macrocyclic precursors to extended carbon sheets are perethynylated dehydroannulenes [56] and expanded radialenes, novel carbon-rich materials with interesting and unusual structures and functions. 

All inert minerals are suitable as extenders. Carbonate-containing extenders may only be used if no stringent requirements have to be satisfied as regards resistance to water and chemicals. 

---