Of triple bonds

Table 7.20 Absorption Frequencies of Single Bonds to Hydrogen Table 7.21 Absorption Frequencies of Triple Bonds Table 7.22 Absorption Frequencies of Cumulated Double Bonds Table 7.23 Absorption Frequencies of Carbonyl Bands...

Dinuclear stmctures are known for molybdenum(III) in a series of air and moisture sensitive compound containing multiple Mo—Mo bonds. Examples include Mo2(N(CH2)2)g (Fig- 5b) and Mo2(CH2Si(CH2)3)g in which there is a strong Mo—Mo bond, presumably of triple-bond character (28). 

It is known that diacetylenes (in Favorsky s reaction, for example) are 1000-fold more active than monoacetylenes. It is of interest to consider how the accumulation of triple bonds will affect the compound acidity. However, in the literature there are no data on the CH acidity of diacetylenic compounds. We were the first to estimate the p/ifa of a monosubstituted diacetylene, 4-butadiynyl-l,3,5-trimethylpyrazole, to be about 24-26 log units. Unfortunately, the authors (83IZV466) have failed to determine the acidity of the diyne more accurately owing to the side processes of remetallization that complicate control over reaction. 

Polya s Theorem clearly showed the way to the general enumeration of all acyclic hydrocarbons, irrespective of how many double or triple bonds they might have but it was to be 35 years before this enumeration was carried out. In two papers [ReaR72,76] I obtained the solution to this general problem in both the structural isomer and stereoisomer cases, as generating functions in three variables. Of these variables, x marks the number of carbon atoms, y the number of double bonds, and z the number of triple bonds. The de- rivation of these generating functions was Polya theory all the way — a succession of applications of Polya s Theorem with occasional use of Otter s result. The derivation was really rather tedious, but the generating functions, once obtained, can be used to compute the... 

Supplement A The chemistry of double-bonded functional groups (2 parts) Supplement B The chemistry of acid derivatives (2 parts) Supplement C The chemistry of triple-bonded functional groups (2 parts) Supplement D The chemistry of halides, pseudo-halides and azides (2 parts) Supplement E The chemistry of ethers, crown ethers, hydroxyl groups and their sulphur analogues (2 parts)... 

Supplement C The Chemistry of Triple-Bonded Functional Groups (two parts)... 

For reviews of triple bonds, see Simonetta, M. Gavezzotti, A., in Patai The Chemistry of the Carbon-Carbon Triple Bond Wiley NY, 1978, p. 1 Dale, J., in Viehe, H. Acetylenes Marcel Dekker NY, 1969, p. 3. 

For a review of the acidity of cyano compounds, see Hibbert, F. in Patai Rappoport The Chemistry of Triple-bonded Functional Groups, pt. 1 Wiley NY, 1983, p. 699. 

As in the case of the base-catalyzed reaction, the thermodynamically most stable alkene is the one predominantly formed. However, the acid-catalyzed reaction is much less synthetically useful because carbocations give rise to many side products. If the substrate has several possible locations for a double bond, mixtures of all possible isomers are usually obtained. Isomerization of 1-decene, for example, gives a mixture that contains not only 1-decene and cis- and franj-2-decene but also the cis and trans isomers of 3-, 4-, and 5-decene as well as branched alkenes resulting from rearrangement of carbocations. It is true that the most stable alkenes predominate, but many of them have stabilities that are close together. Acid-catalyzed migration of triple bonds (with allene intermediates) can be accomplished if very strong acids (e.g., HF—PF5) are used. If the mechanism is the same as that for double bonds, vinyl cations are intermediates. 

However, a number of examples have been found where addition of bromine is not stereospecifically anti. For example, the addition of Bf2 to cis- and trans-l-phenylpropenes in CCI4 was nonstereospecific." Furthermore, the stereospecificity of bromine addition to stilbene depends on the dielectric constant of the solvent. In solvents of low dielectric constant, the addition was 90-100% anti, but with an increase in dielectric constant, the reaction became less stereospecific, until, at a dielectric constant of 35, the addition was completely nonstereospecific.Likewise in the case of triple bonds, stereoselective anti addition was found in bromination of 3-hexyne, but both cis and trans products were obtained in bromination of phenylacetylene. These results indicate that a bromonium ion is not formed where the open cation can be stabilized in other ways (e.g., addition of Br+ to 1 -phenylpropene gives the ion PhC HCHBrCH3, which is a relatively stable benzylic cation) and that there is probably a spectrum of mechanisms between complete bromonium ion (2, no rotation) formation and completely open-cation (1, free rotation) formation, with partially bridged bromonium ions (3, restricted rotation) in between. We have previously seen cases (e.g., p. 415) where cations require more stabilization from outside sources as they become intrinsically less stable themselves. Further evidence for the open cation mechanism where aryl stabilization is present was reported in an isotope effect study of addition of Br2 to ArCH=CHCHAr (Ar = p-nitrophenyl, Ar = p-tolyl). The C isotope effect for one of the double bond carbons (the one closer to the NO2 group) was considerably larger than for the other one. ... 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 15-16). With allqmes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsulfonic acid). ... 

Catalytic hydrogenation of triple bonds and the reaction with DIBAL-H usually give the eis alkene (15-11). Most of the other methods of triple-bond reduction lead to the more thermodynamically stable trans alkene. However, this is not the case with the method involving hydrolysis of boranes or with the reductions with activated zinc, hydrazine, or NH2OSO3H, which also give the cis products. 

In certain cases, Michael reactions can take place under acidic conditions. Michael-type addition of radicals to conjugated carbonyl compounds is also known.Radical addition can be catalyzed by Yb(OTf)3, but radicals add under standard conditions as well, even intramolecularly. Electrochemical-initiated Michael additions are known, and aryl halides add in the presence of NiBr2. Michael reactions are sometimes applied to substrates of the type C=C—Z, where the co-products are conjugated systems of the type C=C—Indeed, because of the greater susceptibility of triple bonds to nucleophilic attack, it is even possible for nonactivated alkynes (e.g., acetylene), to be substrates in this... 

Acylation of Activated Double Bonds and of Triple Bonds... 

In some cases, double bonds add to triple bonds to give cyclobutenes, apparently at about the same rate that they add to double bonds. The addition of triple bonds to triple bonds would give cyclobutadienes, and this has not been observed, except where these rearrange before they can be isolated (see 15-63) or in the presence of a suitable coordination compound, so that the cyclobutadiene is produced in the form of a complex (p. 60). 

For addition of triple bonds to triple bonds, but not with ring formation, see 15-19. 

For a review of these cases, and of cycloadditions of triple bonds to double bonds, see Fuks, R. Viehe, H.G. in Viehe, Ref. 49, p. 435. 

That anti elimination also occurs in the formation of triple bonds is shown by elimination from cis- and trans-HOOC—CH=CC1—COOH. In this case, the product in both cases is HOOCC=CCOOH, but the trans isomer reacts about 50 times faster than the cis compound. ... 

First, we consider reactions in which a C=C or a C=C bond is formed. From a synthetic point of view, the most important reactions for the formation of double bonds are 17-1 (usually by an El mechanism), 17-6,17-12, and 17-22 (usually by an E2 mechanism), and 17-3,17-4, and 17-8 (usually by an Ei mechanism). The only synthetically important method for the formation of triple bonds is 17-12. In the second section, we treat reactions in which C=N bonds and C=N bonds are formed, and then eliminations that give C=0 bonds and diazoalkanes. Finally, we discuss extrusion reactions. 

Addition of unsaturated boranes to methyl vinyl ketones Hydrocarboxylation of triple bonds Addition of acyl halides to triple bonds 1,4-Addition of acetals to dienes... 

Unlike triple-bond participation, no remote cumulative double-bond (allenic) participation in solvolysis has so far been observed or reported. A summary of triple-bond and allenic participation in solvolysis involving possible vinyl cations is given in Table VI. 

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