Carbon compounds nitriles

The analytical data obtained, particularly by the PUMA mass spectrometer on board Vega 1 during the flyby, indicate the presence of a large number of linear and cyclic carbon compounds, such as olefins, alkynes, imines, nitriles, aldehydes and carboxylic acids, but also heterocyclic compounds (pyridines, pyrroles, purines and pyrimidines) and some benzene derivatives no amino acids, alcohols or saturated hydrocarbons are, however, present (Kissel and Krueger, 1987 Krueger and Kissel, 1987). 

The meso-ionic 1,3-oxazol-S-ones show an incredible array of cycloaddition reactions. Reference has already been made to the cycloaddition reactions of the derivative 50, which are interpreted as involving cycloaddition to the valence tautomer 51. In addition, an extremely comprehensive study of the 1,3-dipolar cycloaddition reactions of meso-ionic l,3-oxazol-5-ones (66) has been undertaken by Huisgen and his co-workers. The 1,3-dipolarophiles that have been examined include alkenes, alkynes, aldehydes, a-keto esters, a-diketones, thiobenzophenone, thiono esters, carbon oxysulfide, carbon disulfide, nitriles, nitro-, nitroso-, and azo-compounds, and cyclopropane and cyclobutene derivatives. In these reactions the l,3-oxazol-5-ones (66)... 

Since hydrocarbon subunits (methyl, methylene and methine groups) are not polarized to a great extent, their nature can be defined by a polar substituent. The high acidity of the a-hydrogen atoms of carbonyl compounds, nitriles, sulfones, and nitroalkanes follows from polarity alternation, the carbon atoms being a donor next to the acceptor substituent. 

Compounds with a low HOMO and LUMO (Figure 5.5b) tend to be stable to selfreaction but are chemically reactive as Lewis acids and electrophiles. The lower the LUMO, the more reactive. Carbocations, with LUMO near a, are the most powerful acids and electrophiles, followed by boranes and some metal cations. Where the LUMO is the a of an H—X bond, the compound will be a Lowry-Bronsted acid (proton donor). A Lowry-Bronsted acid is a special case of a Lewis acid. Where the LUMO is the cr of a C—X bond, the compound will tend to be subject to nucleophilic substitution. Alkyl halides and other carbon compounds with good leaving groups are examples of this group. Where the LUMO is the n of a C=X bond, the compound will tend to be subject to nucleophilic addition. Carbonyls, imines, and nitriles exemplify this group. 

The double bonds of electron-deficient olefins (carbonyl compounds, nitriles, sulfones, sulfoxides, nitro derivatives, etc.) have a low-lying LUMO that can allow the attack of various nucleophiles. The nucleophiles can be neutral or negatively charged heteroatomic species, or they can be carbon species such as organometal-lic reagents or enolates. In the case of heteroatomic nucleophiles, asymmetric additions can be performed in the presence of chiral catalysts, with chiral reagents, or with substrates bearing chiral residues. 

In the presence of alkaline catalysts alcohols can undergo nucleophilic addition to the C=C double bond of, / -unsaturated carbonyl compounds, nitriles, sulfones, or sulfoxides. Similarly the doubly bonded carbon atoms in polyfluoroethylenes are susceptible to nucleophilic attack by alcohols in the... 

Since the S-H bond is only slightly polarized and heterolysis to a proton and a mercaptide ion is thus difficult,19 the addition to olefins is preferably carried out by a radical route induced by benzoyl peroxide12 by irradiation with UV light.13 Alkanethiols and thiophenols can be added under the influence of basic catalysts to strongly polar double bonds such as those in unsaturated carbonyl compounds, nitriles, and carboxylic acids, the C-S bond then being formed to the cationic / -carbon atom ... 

Of course a nitrile is not a carbonyl. But nitrile and carbonyl chemistries are similar, and an examination of nitrile reactions naturally belongs in this section. Like carhonyl compounds, nitriles are both electrophiles and nucleophiles. As in carhonyl compounds, a polar resonance form contributes to the structure of nitriles (Fig. 18.44). Consequently, the triple bond is polarized and the carhon acts as a Lewis add. One might antidpate that nudeophiles would add to nitriles, and that idea is correct. These similarities mean that many of the reactions of carhonyl groups are also possible for nitriles, and the mechanisms are generally dosely related. Students sometimes have trouble with the nitrile reactions, however, so it is important not to dismiss them with only a cursory look. For some reason, the analogy between the carbon—oxygen double bond and the carbon—nitrogen triple bond is not always easy to keep in mind. 

Carbon acids such as nitro compounds, nitriles, ketones, anhydrides, esters, and sulfones are also capable of protonating and thereby cleaving these bases with ultimate formation of new carbon-carbon bonds . As expected from equation (6), and as su ested by the variation in reaction conditions used for preparing 88 to 42, ease of reaction diminishes with decreasing substrate acidity. Whereas... 

Transition metal catalyzed hetero-[2+2+2] cycloaddition of alkynes to compounds with a multiple carbon-heteroatom bond such as isocyanates, carbon dioxide, nitriles, aldehydes, and ketones leads to heterocyclic arenes and unsaturated heterocycles. These reactions are classified into two groups coupling of diynes with multiple carbon-heteroatom... 

The lower members of other homologous series of oxygen compounds— the acids, aldehydes, ketones, anhydrides, ethers and esters—have approximately the same limits of solubility as the alcohols and substitution and branching of the carbon chain has a similar influence. For the amines (primary, secondary and tertiary), the limit of solubility is about C whilst for the amides and nitriles it is about C4. 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

The reaction of phosphorus pentasulfide with a-acylamino carbonyl compounds of type Ilia also yields thiazoles. Even more commonly, a mercaptoketone is condensed with a nitrile of type IVa or a-mercaptoacids or their esters with Schiff bases. This ring closure is limited to the thiazolidines. In the Va ring-closure type, /3-mercaptoalkylamines serve as the principal starting materials, and ethylformate is the reactant that supplies the carbon at the 2-position of the ring. These syntheses constitute the most important route for the preparation of many thiazolidines and 2-thiazohnes. In the Vb t3fpe of synthesis, one of the reactant supplies only the carbon at the 5-position of the resultant thiazole. Then in these latter years new modern synthetic methods of thiazole ring have been developed (see Section 7 also Refs. 515, 758, 807, 812, 822). 

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