Bonds to Carbon or Nitrogen

Bonds to Carbon or Nitrogen.— The preparation of dialkoxy- and diphenoxy-stibines from methyldibromostibine and the sodium salts of 

Martinez-Ripoll, A. Haase, and G. Brauer, Acta Cryst., 1974, B30, 2006. 

Thermal or photochemical methods can be used to prepare metal carbonyl complexes from Sb(NMe2)3 715 with the Group VI hexacarbonyls, the products are formulated as Sb(NMe2)3,M(CO)5. 

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The >C = P- and -N = P- bonds, being polar, are attacked by protic reagents resulting in 1,2-addition, the proton being bonded to carbon or nitrogen. 

This shows that the reactivity of the precusor depends on the chemical groups bonded to carbon or nitrogen. Attempts have been made to predict the reactivity between different precursors by quantum chemistry calculations, as for instance the negative electronic charge on the sulfur atom [135, 136]. According to this particular criterion, the reactivity should decrease along the series TA > TC > TU > TSC > ATU, in agreement with some observations. 

Imine. A class of compounds containing a nitrogen double bonded to a carbon on one side and single bonded to carbon or hydrogen on the other side. 

The carbon-carbon double bond is essentially nonpolarized in the rest state, even though, under the influence of an approaching molecule, it is highly polarizable, especially in aromatic systems. When a permanent polarization is introduced, as is the case when carbon is doubly bonded to oxygen or nitrogen, the addition of sodium is greatly facilitated. The carbonyl group provides the most familiar illustration. The sodium reduction of esters is a classic example ... 

Halogen atoms that are involved in halogen-bonding formation can be bound to other halogens (elemental halogens and inter halo gens) or to carbon or nitrogen atoms. The electron-pair donors can be neutral (N, O. S, Se,...) or anionic (1, Br, Cl , F. ..) species. Interaction of these motifs results in a wide diversity of supramolecular synthons (Fig. 1). 

This chapter will deal with compounds in which structures 1 or 2 appear at least once, where the nitrogen atoms are singly bonded to carbon or hydrogen atoms, and furthermore, when these carbon atoms are linked to hydrogen or carbon atoms. Thus structures such as pyrrole (3), morpholine (4), and their salts will be considered, whereas pyridine (6) and 1-aminoethanol will be excluded, in spite of the fact that many of the methods applied in analysing the former compounds are useful for the latter too. 

A nitrogen atom with five valence electrons forms a total of three covalent bonds to carbon or hydrogen atoms in neutral compounds. A nitrogen atom in a functional group can form single, double, or triple bonds. We have discussed all of these functional groups in previous chapters. In this chapter we will focus on amines and amides, but will also discuss the other functional groups that are either the reactants required to form amines and amides or the products of their reactions. 

Nitroparaffias (or nitroaLkanes) are derivatives of the alkanes ia which one hydrogen or more is replaced by the electronegative nitro group, which is attached to carbon through nitrogen. The nitroparaffins are isomeric with alkyl nitrites, RONO, which are esters of nitrous acid. The nitro group ia a nitroparaffin has been shown to be symmetrical about the R—N bond axis, and may be represented as a resonance hybrid ... 

Draw simple molecular orbital energy-level diagrams to indicate how the bonding in the saline hydrides, such as NaH or KH, differs from that between hydrogen and a light p-block element such as carbon or nitrogen. 

Attached by a covalent bond to carbon atom 1 of the deoxyribose ring is an amine (and therefore a base), which may be adenine, A (22) guanine, G (23) cytosine, C (24) or thymine, T (25). In RNA, uracil, U (26), replaces thymine. The base bonds to carbon atom 1 of deoxyribose through the nitrogen of the —NH— group (printed in red) and the compound so formed is called a nucleoside. All nucleosides have a similar structure, which we can summarize as the shape shown in (27) the lens-shaped object represents the attached amine. 

It is quite easy to eliminate two hydrogen atoms via a-elimination from a silicon atom (preferred to a p-elimination with the second hydrogen bonded to a carbon or nitrogen atom). 

Although transition metal-catalyzed allylic alkylation has become one of the most powerful methods in chemical synthesis, the formation of ether bonds using this process has been slow to evolve.119-121 The main reasons for this disparity are the lower nucleophilicity and higher basicity of oxygen nucleophiles, particularly those derived from aliphatic alcohols, compared to their carbon or nitrogen analogs. However, this notion has rapidly been revised, as recent advances in the O-allylation area have largely addressed the issue of the reactivity mismatch between the hard alkoxide and the soft 7r-allylmetal species to provide a considerable body of literature. 

D) Hydrogen bonding is a very strong mtermolecular force that occurs between an H atom of one molecule that is bonded to either a fluorine, an oxygen, or a nitrogen atom. In choice (D), the hydrogens are bonded to carbon, not to F, O, or N. 

Availability of a sample isotopically enriched with 15N and 13C offers the NMR spectro-scopist additional tools for overcoming the problems encountered in homonuclear experiments. In an obvious extension of the homonuclear experiments, the carbon or nitrogen dimension can be used to improve the resolution in NOESY spectra. However, recent trends clearly favor the through-bond approach where the presence of a cross peak unambiguously proves the existence of a chemical bond between the nuclei involved. Let us review briefly the experiments available for labeled oligonucleotides. 

Iodinated contrast agents with polyhydroxylated carbon side-chains contain a number of asymmetric carbon atoms yielding numerous optical isomers which relate to each other as enantiomers or diastereoisomers. Sterically hindered non-asymmetric carbon or nitrogen atoms might result in additional asymmetry centres while the partial double bond character of the acyl-carbon-nitrogen bond of amide functions can lead to cisitrans isomerism. Such isomers are labelled rotamers when heating in solution is able to modify their ratio. Isomerism of iodixanol has been described by Priebe et al. [122], Fossheim et al. [123] and by Molander et al. [115]. 

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