C-l carbon

Mantcll, C. L., Carbon and Graphite Handbook, Robert E. Krieger Publishing Company, Huntington, NY, 1968. 

A final crucial step in this synthesis was an anionic [2,3]-sigmatropic rearrangement of an allylic ether in Step D-4 to introduce the C(l) carbon. 

The reactive nature of compound 22 is illustrated by the series of transformations shown in Scheme 7.12, in which its Zr—C bond reacts selectively with electrophilic reagents to produce a-haloboronates 36—38. Compound 22 also catalyzes the polymerization of styrene. The polymers thus obtained had weight-average molecular masses in the range 75000—100000 with polydispersities of 1.8—2.1. An X-ray analysis of 22 confirmed it to be a four-coordinate Zr complex with two cyclopentadienyl rings, chlorine, and the aliphatic C-l carbon atom as the ligands (Fig. 7.4). 

C.l. Carbon monoxide and carbon dioxide activation assisted by... 

Chapter 8 (section C3) presents stereochemical evidence that the hydrolysis of /3-o-galactosides catalyzed by /3-galactosidase (equation 7.11) involves two successive displacements on the C-l carbon—i.e., involves an intermediate. Further evidence for an intermediate from partitioning experiments is presented in Table 7.10. There is constant partitioning between water and methanol.39-41... 

Lysozyme and /3-galactosidase, which are both glycosidases, catalyze very similar reactions. Both enzymes are found to catalyze the alcoholysis of their polysaccharide substrates with retention of configuration at the C-l carbon (equation 8.25).14-17 This is consistent with the evidence presented in Chapter 7, section C3, that there is at least one (but probably only one) intermediate on the reaction pathway. However, kinetic isotope data are consistent with the interpretation that the intermediate in the reaction of /3-galactosidase is covalent and that there are two successive SN2 displacements, whereas the intermediate with lysozyme is a bound carbonium ion formed in an SN1 reaction (Chapter 16). The carbonium ion, unlike an analogous one in solution, reacts stereospecifically on the enzyme. Thus, the stereochemical evidence by itself has given no indication of the nature of the intermediate. 

The presence of anisotropic motion along the molecular length is suggested for trisaccharide 15 as the anomeric carbons of the a and j8 anomers show different Tl values.85 A smaller T, for the C-l carbon of the a anomer (0.11s) relative to that of the j3 anomer (0.24 s) indicates a close correspondence between the equatorial C-H vector in the a-anomer and the favored axis of rotation. By contrast, relaxation studies on sucrose14,106 (7) did not reveal anisotropic motion (however, see below). 

Figure I. NOEFs for C-l carbon undergoing internal rotation as a function of the...

Table XIII. Calculated Methylene Spin-Lattice Relaxation Times and Nuclear Over-hauser Enhancement Factors for the C-l Carbon...

We note upon inspection of the data in Table XIV that the chemical shifts in these carbonium ions (Via, b, and c) follow the normal order observed when substituents on a fully substituted carbon atom are varied from R = H (most shielded) to CH3 to C6H5 (least shielded), rather than for substituents on an electron-deficient trivalent carbon atom, where the CH3-substituted carbon atom is less shielded than the analogous phenyl-substituted carbon atom (58). This is a rather clear-cut indication that the carbinyl carbon atoms in complexes Via, b, and c are nearly fully bonded and only slightly electron-deficient. The slight increase in shielding of the CH3 carbon when VIb is formed from the alcohol and of the C-l carbon of the phenyl group of Vic provides further confirmation of this. 

Mantell, C,L. "Carbon and Graphite Handbook" Interscience Publ. 

Holecek et al. have measured 13C NMR data for a wide range of dibutyltin(IV) compounds.46 Chemical shifts for C-l to C-4 of butyl groups in simple dibutyltin dialkoxides have values of about 19, 27, 26, and 13 ppm, respectively.46 The chemical shifts of the C-l carbons are somewhat dependent on the nature of the compound and its state of association. For 2,2-dibutyl-l,3,2-dioxastannane, the chemical shift of the butyl C-l was about 20 ppm when the attached tin atom was pentacoordinate, but about 27 ppm when it was hexacoordinate.42... 

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