Olefinic strain energy

TABLE 5. Olefinic strain energy (OS, kcal mol 1) calculated for compounds 31 and 33-35135... 

Relative Rates of Expoxidation by Metachloroperbenzoic Acid in CH2C12 at 0° (227) and Strain (SE) and Olefinic Strain Energies (OS) (kcal/mol) In Dienes 277a, b and 278a, b, the Rate and Strain Energies for the First Double Bond are Given... 

The rates of 1,3-dipolar addition of mesitonitrile oxide to cis- (36a) and frans-cyclooctene (37a) and some other cyclic olefins have been discussed with respect to strain effects (271). It was concluded that frontier orbital energies of the alkenes and differences in olefinic strain energies do not correlate with the observed reactivities. The relative rates for addition of phenyl azide to several alkenes and the olefinic strain energies are shown in Table 31 (272). 

In contrast to the reaction with phenylsulfenyl chloride, 1,3-dipolar reagents react much faster with norbornene (287) than with cyclohexene (42a). It appears as if the rate ratio is correlated with the differential olefinic strain energies. 

Such transient species can be remarkably strained. For example, hydrogen chloride elimination from chloroquadricyclane with f-butyllithium or n-butyllithium/potassium tert-bntoxide leads to the formation of didehydroquadricyclane which can be trapped as a Diels-Alder adduct. The olefinic strain energy (i.e. the difference between the heat of hydrogenation of the strained alkene and that of an unstrained reference alkene) for this alkene was evaluated as 71kcal/mol (Figure 2.28). ... 

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... 

Rotane 83 was similarly prepared from the olefin 82, albeit by a newly modified Simmons-Smith reaction with silver replacing the copper in the above reaction scheme 28). An alternative method from 79 was also reported 28-30). Deductions have been made as to the strain energy of [3]rotane29K... 

The situation is somewhat more favorable for the rearrangement of olefin 27 to give carbene 28. Here, the energy difference of E(28) — E(27) is computed as only 17.3 kcal/mol, indicating the relief of strain energy of 27. 

The location of hydrogen atoms by electron diffraction suffers from some uncertainty, and in order to confirm the state of hybridization of the olefinic carbons, Traetteberg et al. (177) undertook a combined electron diffraction and strain energy calculation study of 1-methyl-frans-cyclooctene. Calculations, us-... 

Maier and Schleyer (220) have studied the problem of the stability of bridgehead double bonds in bi- and polycyclic systems. They define an olefinic strain (OS) as the difference in strain energy between the olefin and its parent saturated... 

However, in many interesting cases, the requisite experimental data are not available, and the olefinic strain for disubstituted alkenes may be estimated using the calculated energies and the following isodesmic reaction ... 

The calculated energy change for this reaction gives the difference in olefinic strain between the alkene and cyclohexene, and the olefinic strain of the latter is negligible. With tri- and tetrasubstituted alkenes, it is more appropriate to use methylcyclohexane or 1,2-dimethylcyclohexane as the unstrained reactant since it is known that alkyl substitution stabilizes double bonds. The values of olefinic strain for a number of alkenes are summarized in Figure 15.2. Compounds with high OS are expected to be relatively reactive. 

Heats of formation, strain energies, and olefinic strain for cycloalkenes. 

Compound A (25 0 Strain Energy kcal/mol Olefinic Strain kcal/mol... 

The estimates of the RSE for small cyclic alkanes, cyclo-olefins, and cyclic ethers using all three reactions are listed in Table 3.21. The failure of the isodesmotic reaction is readily apparent by examining the RSE of the cyclic alkanes. For the rings having five or more carbon atoms, the isodesmic method predicts that there is no strain energy. Rather, it predicts that these cyclic species are more stable than their acyclic counterparts. The homodesmotic and GE reactions, which are identical for the cyclic alkanes, provide RSEs in excellent agreement with CRSE estimates. 

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