Double bond cumulated

CH = C = CH— are called allenes after the simplest member of the series. They are said to have cumulated double bonds. They react in most cases normally, that is, each double bond is unaffected by the proximity of the other they are converted by heating into the isomeric acetylenes. Compounds of the type... 

The cumulated double bonds of an allenic system are of relatively high energy The heat of hydrogenation of allene is more than twice that of propene... 

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...

Table 7.32 Raman Frequencies of Cumulated Double Bonds...

Ketenes and related compounds have been reviewed extensively (1 9). For the synthesis and synthetic uses of conjugated ketenes see Reference 10. Ketenes with three or more cumulated double bonds have been prepared (11,12). The best known is carbon suboxide [504-64-3] 3 2 preparative uses and has been reviewed (13—16). Thioketenes (17,18), ketenimines (19—21), and their dimers show interesting reactivity, but they have not achieved iadustrial importance to date. 

Aldehydes, ketones and cumulated double bonds react with oxiranes to form five-membered heterocycles (e.g. Schemes 31 and 32) (64HC(19-1)453). 

The two most commonly applied systems for naming polycyclic parents are in some ways complementary. Fusion nomenclature provides names for structures containing the maximum number of non-cumulative double bonds von Baeyer nomenclature (Section 1.02.3.4) names fully saturated structures. Thus names for partially hydrogenated structures can be arrived at either by adding hydro prefixes to fusion names or ene , diene , etc. suffixes to von Baeyer names (see examples 29 and 30). If needed, rules are available for... 

The prefixes to be attached to the name of the base component are formed by changing the terminal e of the trivial or Hantzsch-Widman names of the components (in the form containing the maximum number of non-cumulative double bonds) into o . Some prefixes are further abbreviated, as exemplified in the following list ... 

The following prefixes are used to represent monocyclic hydrocarbon components other than benzene cyclopropa-, cyclobuta-, cyclopenta-, cyclohepta-, etc. When a monocyclic hydrocarbon is the base component, it carries the ending ene , signifying the maximum number of non-cumulative double bonds (examples 33 and 34). 

Most parent structures consist essentially of an assembly of rings and/or chains, the degree of hydrogenation of which is defined (usually completely saturated or containing the maximum number of non-cumulative double bonds in cyclic portions), and having no attached functional substituents (the carbohydrates are a notable exception to this). The stereochemistry at all (or most) chiral centres is defined thus such parent structures are sometimes referred to as stereoparents . Some examples are shown (77)-(83). 

The 1,3-dipolar cycloadditions offluonnatedallenes provide a rich and varied chemistry Allenes, such as 1,1-difluoroallene and fluoroallene, that have fluorine substitution on only one of their two cumulated double bonds are very reactive toward 1,3-dipoles Such activation derives from the electron attracting inductive and hyperconjugative effects of the allylic fluorine substituent(s) that give nse to a considerable lowering of the energy of the LUMO of the C(2)-C(3) n bond [27]... 

Section 10.5 Dienes aie classified as having isolated, conjugated, or cumulated double bonds. 

This fundamental discovery dramatically affected the whole chemistry of main-group elements. Subsequently, a series of new compounds with silicon element multiple bonds has been introduced. Within only a few years, stable silenes (silaethenes with a Si = C double bond) [8-11], silaimines Si = N [12-14], and silaphosphenes Si = P [15] were synthesized. As a pacemaker, silicon chemistry has exerted a strong influence on further areas of main-group chemistry a variety of stable molecules with Ge = Ge [16], P = P [17], As = As [18], P = C and P = C [19-22] bonds were subsequently isolated, and systems with cumulated double bonds P = C = P [23-25] are also known today. 

These carbene (or alkylidene) complexes are used for various transformations. Known reactions of these complexes are (a) alkene metathesis, (b) alkene cyclopropanation, (c) carbonyl alkenation, (d) insertion into C-H, N-H and O-H bonds, (e) ylide formation and (f) dimerization. The reactivity of these complexes can be tuned by varying the metal, oxidation state or ligands. Nowadays carbene complexes with cumulated double bonds have also been synthesized and investigated [45-49] as well as carbene cluster compounds, which will not be discussed here [50]. 

Triple bonds and cumulative double bonds 2-Carb-18. Branched-chain sugars... 

Monosaccharide derivatives having a triple bond or cumulative double bonds in the backbone chain are named by the methods of 2-Carb-17.2, with the infix n-yn for a triple bond and infixes such as ij-dien for cumulative double bonds. 

When three, five, or any odd number of cumulative double bonds exist, orbital overlap causes the four groups to occupy one plane and cis-trans isomerism is observed. When four, six, or any even number of cumulative double bonds exist, the situation is analogous to that in the allenes and optical activity is possible. Compound 20 has been resolved. ... 

Participation by cumulative double bonds and vinyl cation intermediates has been suggested in the solvolyses of a number of homoallenyl systems. Hanack and Haffner (87) reported the solvolyses of 3,4-pentadienyl jS-naphthalene sulfonate, 110 (R = H) under a variety of conditions. The products... 

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. 

An interesting carbene, 1-oxobutatrienylidene [25], having cumulated double bonds, has been found by IR spectroscopy in the photolysis (A>230nm) products of matrix-isolated l,2,3,4-pentatetraene-l,5-dione [26] (Maier et al., 1988) (in its turn the unstable dione [26] was generated by thermo- or photo-destruction of compound [27]). The second product was carbon monoxide. The linear structure of the carbene [25] has been suggested on the basis of two intense IR bands at 2222 cm and 1923 cm indicating respectively ketene and allene fragments. 

The double bonds of allene are said to be cumulated because one carbon (the central carbon) participates in two double bonds, i) Hydrocarbons whose molecules have cumulated double bonds are called cumulenes. 

These molecules also have large substituents, and it might seem surprising that the radialene rings avoid puckered conformations in these species. The nonbonded repulsions are, however, reduced in these molecules because of external ring closures (13) or because two of the exocylic CC double bonds involve cumulated double bond systems (14 and... 

Using standard references and protocol, we find the three reactions are respectively endothermic by ca 2, 8 and 6 kJmol-1, or ca 2, 4 and 3 kJmol-1 once one remembers to divide by 2 the last two numbers because the allene is dialkylated. So doing, from equations 10 and 11 we find an average ca 3 kJmol-1 (per alkyl group) lessened stability for alkylated allenes than the correspondingly alkylated alkenes. This is a small difference that fits most naturally in the study of substituted cumulenes such as ketenes and ketenimines, i.e. not in this chapter. But it is also a guideline for the understanding of polyenes with more cumulated double bonds. 

Cycloaddition with nitrile oxides occur with compounds of practically any type with a C=C bond alkenes and cycloalkenes, their functional derivatives, dienes and trienes with isolated, conjugated or cumulated double bonds, some aromatic compounds, unsaturated and aromatic heterocycles, and fullerenes. The content of this subsection is classified according to the mentioned types of dipolarophiles. Problems of relative reactivities of dienophiles and dipoles, regio- and stereoselectivity of nitrile oxide cycloadditions were considered in detail by Jaeger and... 

These considerations led us to the conclusion that suitable triple-bond systems A=B (or compounds containing cumulative double-bond systems A=B=C) might be found that add pyranoses and furanoses under base... 

Intramolecular Radical Additions to Cumulated Double Bonds 716... 

Allene is a versatile functionality because it is useful as either a nucleophile or an electrophile and also as a substrate for cycloaddition reactions. This multi-reactivity makes an allene an excellent candidate for a synthetic manipulations. In addition to these abilities, the orthogonality of 1,3-substitution on the cumulated double bonds of allenes enables the molecule to exist in two enantiomeric configurations and reactions using either antipode can result in the transfer of chirality to the respective products. Therefore, the development of synthetic methodology for chiral allenes is one of the most valuable subjects for the synthetic organic chemist. This chapter serves as an introduction to recent progress in the enantioselective syntheses of allenes. Several of the earlier examples are presented in excellent previous reviews [ ] ... 

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