Sp3-carbon

A second factor that contributes to alkene stability involves bond strengths. A bond between an sp2 carbon and an sp3 carbon is somewhat stronger than a bond between two sp3 carbons. Thus, in comparing 1-butene and 2-butene, the monosubstituted isomer has one sp -.sp3 bond and one sp3-sp2 bond, while... 

Methylcyclohexene will have five sp3-carbon resonances in the 20 to 50 6 range and two s/ -carbon resonances in the 100 to 150 6 range. Methylenecyclohexane, however, because of its symmetry, will have only three sp3-carbon... 

X-ray crystallographic analyses of various 3//-azepines indicate that, like the 1//-azepines, they have a boat conformation.28,36 38,289 In both isolable tautomers of the highly substituted 3//-azepine 11, the hydrogen at the sp3 carbon occupies an equatorial position with the carbon inclined at an angle of 57c to the planar hull. 28 3-[Hydroxy(diphenyl)methyl]-3//-azepine has a similar boat conformation, but with the 3-substituent in the equatorial position.39... 

For substituted anilines (Thompson and Williams, 1977) and for 1-naphthylamine and a series of derivatives thereof (Castro et al., 1986a), k2 and the ratio Ar 2/Ar3 have been determined for nucleophilic catalysis with Cl-, Br-, SCN-, and SC(NH2)2. The values of k2 correspond fairly well to those found for the diazotization of aniline, but those of Ar 2/Ar3 increase markedly in the above sequence (Table 3-1). As k3 is expected to be independent of the presence of Cl- or Br- and to show little dependence on that of SCN- or thiourea, the increase in k 2/k3 for this series must be due mainly to 2. Indeed, the value of log(Ar 2/Ar3) shows a linear correlation with Pearson s nucleophilicity parameter n (Pearson et al., 1968). This parameter is based on nucleophilic substitution of iodine (as I-) in methyl iodide by various nucleophiles. The three investigations on nucleophilic catalysis of diazotization demonstrate that Pearson s criteria for bimolecular nucleophilic substitution at sp3 carbon atoms are also applicable to substitution at nitrogen atoms. 

Nucleophilic displacement of sp3-carbon bonded halide and related... 

Chapters 1 and 2 dealt with formation of new carbon-carbon bonds by reactions in which one carbon acts as the nucleophile and another as the electrophile. In this chapter we turn our attention to noncarbon nucleophiles. Nucleophilic substitution is used in a variety of interconversions of functional groups. We discuss substitution at both sp3 carbon and carbonyl groups. Substitution at saturated carbon usually involves the Sjv2 mechanism, whereas substitution at carbonyl groups usually occurs by addition-elimination. 

Alkylsilanes are not very nucleophilic because there are no high-energy electrons in the sp3-sp3 carbon-silicon bond. Most of the valuable synthetic procedures based on organosilanes involve either alkenyl or allylic silicon substituents. The dominant reactivity pattern involves attack by an electrophilic carbon intermediate at the double bond that is followed by desilylation. Attack on alkenylsilanes takes place at the a-carbon and results in overall replacement of the silicon substituent by the electrophile. Attack on allylic groups is at the y-carbon and results in loss of the silicon substituent and an allylic shift of the double bond. 

The macrolide carbonolide B contains six stereogenic centers at sp3 carbons. Devise a strategy for synthesis of cabonolide B and in particular for establishing the stereochemistry of the C(l)-C(8) segment of the molecule. 

Figure 13 shows the irreversible conversion of a nonconjugated poly (p-phenylene pentadienylene) to a lithiun-doped conjugated derivative which has a semiconducting level of conductivity (0.1 to 1.0 S/cm) (29). Obviously, the neutral conjugated derivative of poly (p-phenylene pentadienylene) can then be reversibly generated from the n-type doped material by electrochemical undoping or by p-type compensation. A very similar synthetic method for the conversion of poly(acetylene-co-1,3-butadiene) to polyacetylene has been reported (30), Figure 14. This synthesis of polyacetylene from a nonconjugated precursor polymer containing isolated CH2 units in an otherwise conjugated chain is to be contrasted with the early approach of Marvel et al (6) in which an all-sp3 carbon chain was employed.

Although it was initially believed that polyacetylene was unstable in contact with water under all conditions, it has been successfully chemically doped in aqueous solutions with no apparent degradation of the material [82] and its electrochemistry has also been investigated [135-137] from which it is clear that no degradation occurs in concentrated aqueous electrolytes. Reaction with water can occur under some circumstances however giving rise to sp3 carbons and carbonyl-type structures [129, 138-141],... 

The bonds between an oxygen and an sp3 carbon atom in alcohols, ethers, or esters are quite resistant to hydrogenolysis. Elevated temperatures and pressures are required to induce C-O bond cleavage and the high temperature can cause the cleavage of the C—C bonds, too. 

Retrorsine (22) was recently used as a model compound in a study of carbon-carbon correlations observed in 1,1-ADEQUATE and INADEQUATE spectra. It was noted by Martin and co-workers51 that modulations of 1Jcc correlations between pairs of sp2 carbons and from an sp3 carbon to an sp2 carbon can lead to gaps in the connectivity network being determined for adjacent carbons (see Figures 7 and 8 and also Section 3.4). In addition to the investigation of the 1,1-ADEQUATE correlations of the... 

The classification of amorphous carbon films according to carbon bond type and hydrogen content can be represented in a triangular diagram, Fig. 6 [e.g., 70]. The comers at the base of the triangle correspond to graphite (100% sp2 carbon) and diamond (100% sp3 carbon). The apex represents 100% H, but the upper limit for formation of solid films is defined by the tie line between the compositions of polyethene, -(CH2) -, and polyethyne, -(CH) -. 

Pings [106], and a neutron diffraction study by Mildner and Carpenter [107], both concluded that there is no clear evidence for sp3 carbon and that the radial distribution functions can be satisfactorily indexed to a hexagonal arrays of carbon atoms. A similar conclusion was reached in a recent neutron diffraction study of activated carbons by Gardner et al [108],... 

A comparison of sp2 and sp3 carbon-palladium-bonded PdCys incorporating heterocycles... 

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