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Diels-Alder reaction characteristics

C, b.p. 170 C (decomp.), has a characteristic odour. It is the Diels-Alder product of cyclopentadiene reacting with itself, the exo-form being formed most rapidly but the endo-form is thermodynamically favoured. At temperatures above ISO C a retro-Diels-Alder reaction occurs and cyclopentadiene monomer is regenerated see diene reactions. [Pg.135]

Solvents exert their influence on organic reactions through a complicated mixture of all possible types of noncovalent interactions. Chemists have tried to unravel this entanglement and, ideally, want to assess the relative importance of all interactions separately. In a typical approach, a property of a reaction (e.g. its rate or selectivity) is measured in a laige number of different solvents. All these solvents have unique characteristics, quantified by their physical properties (i.e. refractive index, dielectric constant) or empirical parameters (e.g. ET(30)-value, AN). Linear correlations between a reaction property and one or more of these solvent properties (Linear Free Energy Relationships - LFER) reveal which noncovalent interactions are of major importance. The major drawback of this approach lies in the fact that the solvent parameters are often not independent. Alternatively, theoretical models and computer simulations can provide valuable information. Both methods have been applied successfully in studies of the solvent effects on Diels-Alder reactions. [Pg.8]

In the area of moleculady designed hot-melt adhesives, the most widely used resins are the polyamides (qv), formed upon reaction of a diamine and a dimer acid. Dimer acids (qv) are obtained from the Diels-Alder reaction of unsaturated fatty acids. Linoleic acid is an example. Judicious selection of diamine and diacid leads to a wide range of adhesive properties. Typical shear characteristics are in the range of thousands of kilopascals and are dependent upon temperature. Although hot-melt adhesives normally become quite brittle below the glass-transition temperature, these materials can often attain physical properties that approach those of a stmctural adhesive. These properties severely degrade as the material becomes Hquid above the melt temperature. [Pg.235]

In keeping with its aromatic character, pyrrole is relatively difficult to hydrogenate, it does not ordinarily serve as a diene for Diels-Alder reactions, and does not undergo typical olefin reactions. Klectrophilic substitutions are the most characteristic reactions, and pyrrole has often been compared to phenol or... [Pg.356]

In the Diels-Alder transition state, the two alkene carbons and carbons 1 and 4 of the diene rehybridize from sp2 to sp 5 to form two new single bonds, while carbons 2 and 3 of the diene remain sp2-hybridized to form the new double bond in the cyclohexene product. We ll study this mechanism at greater length in Chapter 30 but will concentrate for the present on learning more about the characteristics and uses of the Diels-Alder reaction. [Pg.493]

Diels-Alder reaction, 492 characteristics of, 492-497 dienes in, 496-497 dienophiles in. 493-494 electrostatic potential map of. 493 endo stereochemistry of, 495 HOMO in. 1188-1189 LUMO in. 1188-1189 mechanism of. 493 s-cis diene conformation in, 496-497... [Pg.1294]

The salt is a colorless crystalline solid which is virtually insoluble in all common organic solvents. It reacts slowly with chloroform and carbon tetrachloride to give thallium(I) chloride 25), gives a characteristic red coloration with carbon disulfide, and undergoes the Diels-Alder reaction with maleic anhydride 110). It is rapidly decomposed by acids, but is stable to water this latter fact has been interpreted (55) in terms of the small free energy change for the reaction... [Pg.149]

As shown in (5.84b), the characteristic feature of the Diels-Alder reaction is the addition of an ethylenic double bond (dienophile) across the 1,4-positions of a conjugated diene to give a cyclohexene ring product. The ethylenic bond is usually... [Pg.686]

Among chiral auxiliaries, l,3-oxazolidine-2-thiones (OZTs) have attracted much interest for their various applications in different synthetic transformations.2 Such simple structures, directly related to far better known chiral oxazolidinones,11,12,57 have been explored in asymmetric Diels-Alder reactions and asymmetric alkylations, but mainly in condensation of their /V-acyl derivatives with aldehydes. Chiral OZTs have shown interesting characteristics in anti-selective aldol reactions58 or combined asymmetric addition. [Pg.146]

This theory proves to be remarkably useful in rationalizing the whole set of general rules and mechanistic aspects described in the previous section as characteristic features of the Diels-Alder reaction. The application of perturbation molecular orbital theory as an approximate quantum mechanical method forms the theoretical basis of Fukui s FMO theory. Perturbation theory predicts a net stabilization for the intermolecular interaction between a diene and a dienophile as a consequence of the interaction of an occupied molecular orbital of one reaction partner with an unoccupied molecular orbital of the other reaction partner. [Pg.340]

Diels-Alder reactions (and other cycloadditions) are accelerated in water due to a combination of enforced hydrophobic interactions and hydrogen bonding, their relative contributions depending on the nature of the diene and dienophile. Subsequent work has shown that a large variety of other organic reactions show comparable favorable characteristics in aqueous media. [Pg.169]

In analogy to olefins, Cjq undergoes a broad variety of cycloadditions (see Chapter 4 and Scheme 14.3). In many cases cycloadducts of Cjq exhibit the same stability as the corresponding non-fullerene based adducts. These reactions are very useful for the introduction of fimctionat groups. Among the most important cycloadditions are [4-1-2] cycloadditions such as Diels-Alder and hetero-Diels-Alder reactions, where Cjq reacts always as dienophile, [3-1-2] cycloadditions with 1,3 dipoles, thermal or photochemical [2-1-2] cycloadditions, [2-t-l] cycloadditions and others, for example, [8-1-2] cycloadditions. Among these general reactions several examples deserve special attention, since they reflect characteristic chemical properties of Cjq [36] ... [Pg.387]

The product 6 of the Diels-Alder reaction between 4 and 5 shows sigmoidal characteristics, indicating that selfreplication is taking place, that is, the product formed is an efficient catalyst for the original Diels-Alder reaction (Scheme 2) <1997CC1495>. [Pg.716]

All three of these retro-Diels-Alder reactions give excited diene intermediates that decay in comparable times the x values range from 150 to 230 fs. The exact structural characteristics of these intermediates is currently unclear. Perhaps this issue could be addressed using femtosecond spectroscopic studies applying laser-induced fluorescence techniques, or through theory-based approaches. [Pg.918]

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... [Pg.192]

The synthetic importance of these reactions is very great and, because many of them often involve dienes, we will discuss their general characteristics in this chapter. The most valuable cycloaddition reaction almost certainly is the [4 + 2], or Diels-Alder, reaction and will be discussed in detail. [Pg.493]

The characteristic feature of all pericyclic reactions is the concertedness of all the bond making and bond breaking, and hence the absence of any intermediates. Naturally, organic chemists have worked hard, and devised many ingenious experiments, to prove that this is true, concentrating especially on the Diels-Alder reaction. The following is an oversimplified description of some of the most telling experiments. [Pg.31]

The characteristic feature of the aforementioned oxazaborolidine catalyst system consists of a-sulfonamide carboxylic acid ligand for boron reagent, where the five-membered ring system seems to be the major structural feature for the active catalyst. Accordingly, tartaric acid-derived chiral (acyloxy)borane (CAB) complexes can also catalyze the asymmetric Diels-Alder reaction of a,P-unsaturated aldehydes with a high level of asymmetric induction [10] (Eq. 8A.4). Similarly, a chiral tartrate-derived dioxaborolidine has been introduced as a catalyst for enantioselective Diels-Alder reaction of 2-bromoacrolein [11] (Eq. 8A.5). [Pg.468]

From all the above calculations, one arrives at a conclusion that 1,2-dihydrodiazetes are simply constrained nonaromatic heterocycles that do not benefit from aromatic stabilization. Also, these compounds undergo facile Diels-Alder reactions or bromination reactions, with no tendency to regain the 7t-structure and are thus characteristic for typical nonaromatic compounds. [Pg.628]

During the Diels-Alder reaction [1] and in the electrocyclization of cis-1,3,5-hexatriene [2], bonds break and form in a homolytic fashion, with orbitals remaining associated with the same centres throughout the reaction. For such systems, there is a major recoupling of the electron spins. This last takes place most rapidly at or near the transition state. The resonance pattern, taken together with other characteristics, is reminiscent of the spin-coupled description... [Pg.51]


See other pages where Diels-Alder reaction characteristics is mentioned: [Pg.728]    [Pg.728]    [Pg.11]    [Pg.61]    [Pg.261]    [Pg.62]    [Pg.493]    [Pg.493]    [Pg.497]    [Pg.168]    [Pg.106]    [Pg.107]    [Pg.450]    [Pg.190]    [Pg.982]    [Pg.46]    [Pg.100]    [Pg.44]    [Pg.1049]    [Pg.1068]    [Pg.39]    [Pg.341]    [Pg.341]    [Pg.84]    [Pg.1030]    [Pg.675]    [Pg.256]    [Pg.725]    [Pg.95]    [Pg.853]   
See also in sourсe #XX -- [ Pg.492 , Pg.493 , Pg.494 , Pg.495 , Pg.496 ]

See also in sourсe #XX -- [ Pg.492 , Pg.493 , Pg.494 , Pg.495 , Pg.496 ]

See also in sourсe #XX -- [ Pg.511 ]




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