Methylene experimental determination

The results of this type of experiment show that CH2 itself is usually formed as a singlet species, that can decay to the triplet state, which consequently has a lower energy (MO calculations and experimental determinations show that the difference in energy between singlet and triplet CH2 is 8-10kcal mol or 33-42 kJ moP ). However, it is possible to prepare triplet CH2 directly by a photosensitized decomposition of diazomethane.Methylene (CH2) is so reactive " that it generally reacts as the singlet before it has a chance to decay to the triplet state. 

The authors also reconsidered radical 20, which, in the current work, was formed by x-irradiation and studied at 77 K. The experimentally determined hyperfine coupling tensors for the two methylene protons have the same principal values and agreed with the tensors found in the earlier work.16 These tensors are presumed to be the average of the two individual proton tensors. By assuming that C5 is sp2 hybridized the authors were able to calculate, from the observed average tensors, that Ami = 1.06 mT and Amai = 3.45 mT for the methylene protons. Using the individual tensors for the methylene protons and a 3.6 mT isotropic coupling for the C4(H) proton, a satisfactory simulation of the... 

Methylene itself has a triplet ground state. The best experimental determinations of... 

Fig. 6. Summary of the standard oxidation-reduction potentials of several dyes and the experimentally determined rate constants for their reduction by P430 . [DP, dipyridyls, preceded by the redox-potential values M(B)V, methyl (benzyl) viologens ST. safranine T MB, methylene blue]. Figure source Ke (1973) The primary electron acceptor of photosystem I. BiochimBiophysActa301 29.

As might be expected from the fact that the extra methylene group in the glutamate side-chain makes the carboxylic acid group less acidic than that of aspartate, in only one family, where the stereochemistry is not experimentally determined (90), is there any suggestion of a system where glutamate is the base and aspartate is the acid. 

The characteristic ratio of the poly(methylene) chain, which might be considered to be the simplest polymer molecule, as a function of chain length is shown in Fig. 4.4 for the simple models considered thus far. All save the simple freely jointed chain display end effects, manifest by an increase in Ci with chain length at small n, which will not be considered further. In what follows, only the asymptotic limit of the characteristic ratio for 00 (Coo) will be discussed. The values of for the freely jointed chain, the freely rotating chain and the chain with independent bond rotational potentials increase in value from 1 through 2 to ca 3-5. The latter value is, however, only ca one-half of the experimentally determined value of Coo=6-9 for poly(methylene). This serious discrepancy points to the fact that the bond rotational potentials are definitely not independent, i.e. the conformation of bond i depends upon the conformations of bonds (/—I) and (/-i-1). 

Lengel. R.K. and Zare. R.N. (1978) Experimental determination of the singlet-triplet splitting in methylene. Journal of the American Chemical Society. 100, 7495-7499. 

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