Cyclohexane isotopically labelled

The d° metals can also carry out alkane activation. In the classic example from Watson [126], exchange occurs at 70°C and is detected by isotope labeling. No reaction with the cyclohexane solvent occurs (Eq. 2.45). 

The initial yields of the ions have been determined from gamma radiolysis in cyclohexane at a pressure of 55 torr by isotopic labelling techniques. In Table 6 we show the initial yields of the various ions together with those obtained from mass-spectrometric determinations at very low pressure. The yields are given as ion-pair yields, i.e. the yield of species per ion pair produced. The ion-pair yield M/N can be converted into species produced per unit energy absorbed, by multiplication by the yield of ionization G = 4.4 (lOOeV)" We see that the decomposition of the parent ion is appreciably suppressed in the gas at 55 torr, due to collisional deactivation. 

A further point that emerges in such studies on polymers is that isotopic labelling can sometimes significantly alter the behaviour of a polymer solution or blend. Detailed studies of the system polystyrene/cyclohexane have been... 

In contrast to this report, a surprising result was obtained by Chen and co-workers by studying with electrospray tandem mass spectrometry the C-H activation in -pentane, cyclohexane, and benzene by Bergman s catalyst [Cp Ir(PMe3)Me]. Neither the oxidative addition/reductive elimination nor the concerted cr-bond metathesis mechanism was found to be operative. Rather, an elimination/addition mechanism through Ir(m) intermediates was proposed and confirmed by isotopic labeling. 

In order to ensure the source of oxygen atom incorporated in the products formed, 0 labelling experiments were carried out for the oxidation of two sample substrates [4] cyclohexane (saturated) and cyclohexene (unsaturated) by using a 50 50 isotopic mixture of... 

The suitability of the system DBr/AlBr3 for deuterium labeling is further underlined by the fact that even the C-H bonds of saturated aliphatic hydrocarbons are attacked isotope exchange with cyclohexane reaches equilibrium in somewhat more than 10 hours. 

Cyclohexane dehydrogenation represents another classical example for isotopic studies. Balandin s sextet mechanism predicted direct dehydrogenation of cyclohexane over several metals, assuming a planar reactive chemisorption of the reactant. Cyclohexene is also readily dehydrogenated to benzene. The use of hydrocarbons labelled with established the true reaction pathway. T6tenyi and co-workers[ °di] reacted a mixture of [ 0]-cyclohexane and inactive cyclohexene on different metals and measured the specific radioactivity of the fractions (cyclohexane, cH, cyclohexene, cH= and benzene, Bz) in the product at low conversion values (Table The... 

Another important observation was provided even before the Dewar papers, namely that the secondary deuterium kinetic isotope effect (SDKIE), at C4 of a 3,3-dicyano substituted-1,5-hexadiene was a larger normal effect in an absolute sense than the inverse SDKIE at C6. This must represent more bond breaking at C4, i.e. rehybridization from sp to sp, than bond formation at C6 involving rehybrization from sp to sp, a result inconsistent with a diyl-like transition state whose SDKIEs would be opposite in magnitude. Subsequent SDKIE determination by Conrad on 3-aIkyl substituted -1,5-hexadiene and 2-phenyl-l,5-hexadiene and on carbon-13 labeled 2,5-diphenyl-1,5-hexadiene revealed a change in transition state structure from a species with more bond making than breaking to one with a nearly a fully formed 1,4-cyclohexane diyl in that order. 

C]-labeled -hexane plus inactive 1-hexene, the isotopic composition of benzene and unreacted hexene in the product was nearly equal (Fig. 2), indicating that all benzene molecule should have involved a hexene intermediate. In turn, hardly any radioactivity appeared in the residual inactive cyclohexane reacted in a... 

Chaney and co-workers investigated the in vitro biotransformations of oxaliplatin and other Pt-DNA adducts containing trans-(7, 7 )-1,2-diamino-cyclohexane carrier ligand in rat blood by H-isotope tracing and found that their decay in the plasma ultrafiltrate occurred rapidly (t < 1 h). Size-exclusion HPLC coupled on-line to ICP-MS was utilized to directly monitor early protein biotransformations of Pt-labeled oxaliplatin following its intravenous administration to cancer patients. It was found that oxaliplatin is almost equally bound to y-globulins and albumin (40% of the Pt bound respectively), in consistence with a previous in vitro study. ... 

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