Cyclohexane deuteriation

In Table 153,198-204.231 ij i3( i3q values of several cyclic and bicyclic alkanes are collected. For symmetric compounds like cyclohexane, deuteriated species are usually investigated because the deuterium label removes the equivalence of the carbon atoms and allows observation of the coupling constant. 

The time-resolved, chemical behavior of FL depends on the solvent. Irradiation of DAF in cyclohexane gives FLH The lifetime of FL in cyclohexane is 1.4 ns, and the ratio of products obtained (26) indicates that both direct insertion and abstraction-recombination mechanisms are operating (Griller et al., 1984b). Replacement of the cyclohexane by its deuteriated counterpart reveals a kinetic isotope effect of ca 2 (Table 5). 

The rates of reaction of OH with methane, deuteriated methanes,228 cyclohexane,229 and 1-bromopropane230 have been measured and the atmospheric implication of the results discussed. The latter study assessed the global warming potential of the industrial solvent 1-bromopropane at 20, 100 and 500 years. 

During the reductive isomerization of 7/3-methyl- 14-isoestr-4-ene-3,17-dione 272 in HF SbF5/methylcyclopentane at 0°C, it was found879 that a 1,3-hydride shift occurs followed by kinetically controlled hydride transfer (Scheme 5.91). The mechanism of the reaction was confirmed by employing the deuteriated donor cyclohexane- as well as a specifically deuterium-labeled starting steroid. 

Pincock and his co-workers have studied the photochemical fragmentation reactions of the esters (31). This system has an in-built electron accepting sensitiser. When (31a-c) are irradiated in methanol the principal reaction is fission to yield the styrene (32) and p-cyanobenzoic acid. The other products formed from the reactions are the styrene addition products (33)-(35). The authors propose that the Norrish T) e II process in this instance involves a proton transfer and this occurs within the zwitterionic biradical formed as the primary intermediate on electron transfer. Further proof of the authenticity of this mechanism was obtained by irradiation of the deuteriated derivatives (31 d, e). The results of a study of the photochemical decomposition of benzyl phenylacetate, as a suspension in water over Ti02, have been reported. Bond fission is the result of irradiation of (36) in cyclohexane/ethyl acetate. A Norrish Type II hydrogen abstraction occurs with the elimination of the enone moiety. This affords a path to the CD ring system (37) of vitamin D. 

Ja,a, are now all H-D coupling and first order. These cause unresolvable splittings to occur which were removed by a strong irradiation at the deuterium resonance frequency (Bloom and Shoolery, 1955), Both of these studies of deuteriated cyclohexane are in agreement and suggest a virtually temperature-independent AG+ value of 10-3-10-5 kcal mole , JH+ = 10-9 + 0-6 kcal mole and AS+ = 2-9 + 2-3 e.u. A transmission coefficient of 0-5 is assumed in the inversion process. The r ults obtained by Harris and Sheppard (1961) have been recalculated and the values of JH+ and AS= now agree with the results on deuteriated cyclohexane. 

Accurate n.m.r. parameters have been obtained for a series of specifically deuteriated methyl- and t-butyl-substituted cyclohexanes with the aid of deuterium decoupling and computer simulation and iteration of the spectra. In [3,3,5,5- H J-methylcyclohexane (40) no change in the value of — 3 6 Hz was noted with... 

The temperature-dependence of the n.m.r. spectrum of deuteriated dispiro-3-cycIohexane-l,2,4,5-tetrathian-6-cyclohexane revealed that at — 12 C the twist conformation (189) was more stable than the chair (190)... 

At temperatures where the ring inversion (47) is fast, 1,1,3,3-tetramethyl-cyclohexane shows only one averaged methyl signal in its C nmr spectrum. The degeneracy of the fast conformational equilibrium is lifted in [52] which has one deuteriated methyl group. This leads to a splitting of the averaged... 

Gunther and Aydin (1981) have investigated the conformational equilibrium (59) in di-cyclohexane. The two conformational isomers [65a] and [65b] with deuterium in the axial and in the equatorial position can be frozen out in the 100 MHz C spectrum below — 80 C. The deuteriated carbons in the two isomers have different intrinsic isotope shifts which are upheld compared to the nondeuteriated carbons. The triplet with the smaller coupling constant was assigned to the carbon with axial deuterium and was shifted 0.0482 ppm to higher held than the triplet caused by the carbon with equatorial deuterium. 

At room temperature the averaged signal for the deuteriated carbons was observed slightly (0.01148 ppm) downheld from the average value expected for an unperturbed equilibrium. This indicates that K 1 and that the equilibrium (59) is shifted in favour of conformation [65b] with deuterium in the equatorial position. The small effect was conhrmed by two independent experimental observations. In a mixture of Dq-, D,- and l.l-Dj-cyclohexane, the deuteriated carbon in D,-cyclohexane showed an upheld shift which was 0.01689 ppm, less than half the value of the intrinsic upheld shift in... 

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