Dioxetanes ring strain

About 30 years ago, an enthalpy of formation was reported for 3,3,4,4-tetramethyl-l,2-dioxetane . Both by direct microcalorimetric combustion measurements of the neat solid and by reaction calorimetry (of the solid itself, and in acetone solution to form acetone), a consensus value was derived. Now, is the enthalpy of formation plausible , notwithstanding the very large error bars Consider reaction 6 for the dioxetane that produces 2,3-dimethyl-2,3-butanediol . The liquid phase enthalpy of reaction is —329 kJmoU. It is remarkable that this value is compatible with that for the dialkyl peroxides, ca —335 kJmoU, despite the ring strain that might be expected. 

Dioxetanes are highly endothermic compounds. This is partly due to ring strain, but above all to the low bond energy of the peroxide bond. 

See Other DIOXETANES, STRAINED-RING COMPOUNDS CYCLIC PEROXIDES... 

Singlet oxygen reacts with electron rich or highly strained alkenes to form 1,2-dioxetanes. These four-membered ring peroxides decompose on warming to two carbonyl compounds (or moieties), usually with appearance of light emission (chemiluminescence). The macrocyclic bis-lactone in (6.17)608>, a musk fragrance, has been synthesized via such a sequence. 

A recent theoretical study on the effect of substituents on the strain energies of small ring compounds has provided some valuable insight into the differences between 1,2-dioxetanes and 1,3-dioxetanes <2002JOC2588>. The C-H bonds within 1,2-dioxetane have been calculated to be stronger than those within 1,3-dioxetane by some 8 kcal mol-1 at the G2 level of theory. Calculations at the same level of theory indicate that 1,2-dioxetane is more strained than 1,3-dioxetane by some 6 kcal mol-1. Somewhat surprising is that this study has also shown that 1,2-dioxetanes are more strained than dioxiranes by some 7-12 kcal mol-1, which is in stark contrast to the case for the parent hydrocarbons and our expectations. The vibrational frequencies and the moments of inertia have also been calculated for the parent 1,2- and 1,3-dioxetanes <1997PGA2471>. 

See other dioxetanes, strained-ring compounds cyclic peroxides... 

Peroxide oxidation in the other compounds, on the other hand, generates a strained four-membered dioxetane or dioxetanone ring which, upon cleavage, releases its energy to the rest of the molecule or a fluorescent species present in the reaction medium. The light emitted in this case is from the fluorescent species as it returns to the ground energy state. 

Recent efforts to report and to repair mechanical damage with mechanochemical reactions form the subject of the current chapter. We start with a brief discussion of the use of the spiropyran unit as a mechanophore for reporting strain. Spiropyran mechanochemistry inspired the development of another stress probe, the highly sensitive mechanoluminescent dioxetane, whose application as scission reporter in several types of polymeric materials is discussed. The chapter continues with a description of recent efforts to develop productive mechanochemistry, where initial scission leads to the formation of new bonds. Bond formation is either induced by the scission of covalent bonds, e.g. by the opening of rings, or bonds are formed under the action of a latent catalyst when it is activated by mechanochemical dissociation of a Lewis acid-base pair. These examples of productive mechanochemistry offer exciting possibilities to develop new modes of self-healing in... 

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