Olefins strained hydrocarbons

Adam W, Oppenlander T (1986) 185-nm Photochemistry of Olefins, Strained Hydrocarbons, and Azoalkanes in Solution, Angew. Chem. Int. Ed. Engl. 25 661-672. 

The strained-ring compound 1,1-dimethyl-l-silacyclobutane (which may be regarded as an olefin of organosilicon chemistry) reacts with diiron nonacarbonyl in benzene at 6°-20°C as shown in Eq. (100) (89). (There is here some analogy with the reactions of transition metal complexes with strained hydrocarbons, which often produce valence tautomerization.) The... 

The next four procedures describe the preparation of strained ring systems. Preparation of 3-CHLORO-2-(CHLOROMETHYL)-l-PROPENE provides a facile approach to the olefin required for the synthesis of [1.1.1 [PROPELLANE, one of the most strained hydrocarbons prepared to date. The ready availability of this hydrocarbon should prove particularly useful to those interested in the development of the chemistry of this fascinating compound. Preparation of N-BENZYL-2,3-AZETIDINEDIONE provides an efficient approach to the unadorned a-keto-/3-lactam, a potential... 

All the amendments to Bredt s rule that have been presented in the past decade have been more or less violated. One reason for these failures is that the past rules ignored the strain in parts of the molecule other than at the bridgehead double bond. Schleyer defines the strain at the bridgehead double bond, or olefin strain (OS), as the difference in strain between the olefin and the parent hydrocarbon, analogous to for carbonium ions (293). He... 

In extensive studies of strained hydrocarbons [79,122-127], we have shown that their C—C bonds have negative potentials (which is unusual for C—C single bonds) and that these are stronger for three-membered rings, which also have a higher degree of strain than four-membered ones. These factors presumably account for the 7s,mm noted above. In all of these respects, the three-membered rings are similar to ethylene, and indeed both 7 and 8 have some olefin-like reactive properties [128-131]. 

The successful inner phase stabilization of cyclobutadiene suggests that this approach may allow stabilization of other molecules with highly strained multiple bonds. An interesting class of hydrocarbons with twisted C=C bonds are anti-Bredt bridgehead olefins. These bicycloalkenes have a trani-cycloalkene and are unstable if their olefinic strain (OS) is OS > 21kcalmor. Bicyclo[2.2.2]oct-l-ene 60 and (Z)-bicyclo[3.2.1]oct-l-ene... 

In the presence of transition metal complexes, certain strained hydrocarbon systems are activated under mild thermal conditions and undergo characteristic transformations. Methylenecyclopropane (XXVI) (Noyori et al., 1970, 1972b), bicyclo[2.1.0]pentane (XXVII) (Noyori et al., 1971c, 1974a), and quadricyclane (XXVIII) (Noyori et al., 1975a) add to electron-deficient olefins with the aid of a nickel(0) catalyst such as bis(l,5-cyclooctadiene)-nickel(O) or bis(acrylonitrile)nickel(0). These cycloaddition reactions proceed... 

Olefin strain energy has been defined as the difference between the strain energies of an olefin and the corresponding saturated hydrocarbon. Generally, the olefin is more strained than the alkane. Given the experimental heats of formation (in kcal / mol) below, calculate the olefin strain for the olefins shown. Comment briefly on the implications of your findings. For some systems, the olefin is actually less strained than the alkane. These have been termed hyperstable olefins. Are any... 

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

While we know of no experimental thermochemical data for 123, Roth informs us that the enthalpy of formation of 124 is 259 kJmol-1. There are no experimental thermochemical data for 125 either, but it is easy to estimate the desired enthalpy of formation. We may either use the standard olefin approach with ethylene, 1,3-butadiene and (E)-l,3,5-hexatriene (i.e. with CH2=CH2, 33 and 79) or linearly extrapolate these three unsaturated hydrocarbons. From either of these approaches, we find a value of ca 225 kJ mol-1. Cross-conjugation costs some 35 kJ mol-1 in the current case. Interestingly, the directly measured cross-conjugated 1,1-diphenylethylene (126) is only ca 10 kJmol-1 less stable than its directly measured conjugated (E)- 1,2-isomer (40) despite the expected strain effects that would additionally destabilize the former species. 

Many other ion-molecule reactions involving highly unsaturated hydrocarbon ions and neutral olefins or the equivalent strained cycloalkanes have been studied by mass spectrometry98. For example, we may mention here the addition of ionized cyclopropane and cyclobutane to benzene radical cations giving the respective n-alkylbenzene ions but also isomeric cyclodiene ions such as ionized 8,9-dihydroindane and 9,10-dihydrotetralin, respectively. Extensive studies have been performed on the dimerization product of charged and neutral styrene4. 

Dioxiranes are three-membered cyclic ring peroxides that are expected to be very unstable owing to ring strain. They are effective oxygenating agents for epoxidations of olefins, allenes, polycyclic aromatic hydrocarbons, enols. and a, /i-unsaturated ketones for insertions of oxygen into X—H... 

It has been observed that the formation of the olefin and carbon monoxide, 45, is ten times more important than the formation of the bicyclic hydrocarbon and carbon monoxide, 46, at 80° and 80 mm. pressure even at 3130 A. The formation of the strained bicyclic hydrocarbon is evidently not a favorable reaction although this may not be the only consideration. In the case of camphor it should be interesting to find out if an optically active isomer of the ketone on photolysis will give rise to an optically active trimethyl bicyclo [2.1.1] hexane (XXVI). A concerted reaction, analogous to the formation of cyclobutane from cyclopentanone, may lead to only an optically active product. 

Every teacher of the first course of organic chemistry, towards its beginning, emphasizes the different behavior of saturated and olefinic hydrocarbons towards halogens. The influence of ring strain is discussed rather later in the course. And a good thing too, for... 

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