Propellanes strain energy

Considering their high expected strain energy, [1.1.1 [propellane and its derivatives possess substantial thermal stability. The neat parent hydrocarbon la is moderately stable at room temperature, particularly in the absence of air, but after a few hours, a considerable amount of polymer builds up36 37. A 3-5% solution can be stored in a refrigerator for weeks without noticeable losses. 

The same group" elegantly synthesized 58, which possesses a strain energy ca. 15-20 kcal mol greater than that of the parent [3.1.1]propellane, 42, and determined the C-NMR spectrum in C Dg/furan (1 1) at — 30°C. The spectrum of 58 includes rather low field absorptions for C(8), 65.5 ppm CJqh — PP (... 

The reverse reaction from the dibromide to the propellane parent had already been reported by electrochemical means . The diiodide 74 gives [3.2.1]propellane with t-BuLi at - 77°C. Reduction of 72 and the dichloride 75 give 76. The length of the conjoining bond in 8,8-dichloro[3.2.1]propellane is 1.572 Its minimum strain energy was estimated to be 60 kcal mol" ... 

Fig. 13.3 Strain energies (SE) of propellanes from homodesmotic reactions [26, 27, 28] at the MP2/6-31G level, without ZPE. The three SEs in parentheses are from [29]. Quantities are atomic units (hartrees) and kJ mol" ...

To discuss and compare theoretically defined strain energies with those defined in terms of the experimental heats of formation for the cyclic, bicyclic and propellane molecules, we shall define group energies in the same manner as is done using the experimental heats of formation except that they will not be referenced to the standard states of the elements. The strain energy of a given group in a molecule is obtained by... 

I 1.50a is an example of a class of molecules called propellanes. The strain energy of the molecule has been estimated to be about 90 kcal/mol [34] so one might think that the molecule may not exist. The central C—C a bond is expected to... 

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