Hydrogen losses

Substituted aromatics, eg, aLkylbenzenes, sometimes experience attack at the substituent position by NO/ (7). A cyclohexadienyl cation is formed it is unstable and the nitro group migrates on the ring to a carbon atom that is attached to a hydrogen. Loss of the proton results in a stable nitroaromatic. 

DR. JACK NORTON (Colorado State University) One interesting result that has just appeared is Ray Sweany s report of photochemical hydrogen loss from iron tetracarbonyl dihydride [Sweany, R. L. J. Am. Chem. Soc. 1981, 103, 2410]. This system is very close to the case in which I claimed some years ago that this process did not occur. First of all, do you have any possible explanations for the differing behavior Why is Sweany s result different from the result of Tony Rest Second, if hydrogen eliminates in a concerted process such as you have just described, why don t other species such as cis-methyl groups do likewise ... 

DR. GEOFFROY We obviously don t know why the photochemistry changes. We know that it is reasonable that phosphine dissociation does not occur when we have a chelating diphosphine ligand. But we don t understand why we see hydrogen loss in this system when we don t see it in the other cases. 

DR. GEOFFROY The 366 nm irradiations are clearly into the lowest absorption band. It is often a tail in these complexes. Unfortunately, the electronic structures of these compounds, as with most all organo-metallic systems, are not well-understood or well-defined. We could interpret the absorption spectrum in several different ways, and we could rationalize why we see hydrogen, depending on how we interpret the absorption spectrum. No matter what we do, we can rationalize hydrogen loss. But it is not very satisfying, because we do not know what the nature of the excited states is. That is an area which needs considerable study, to define the electronic structures of these kinds of compounds. 

The molecular ions of toluene and cycloheptatriene are capable of mutual isomerization prior to dissociation. [49,53,56] It has been known for long that hydrogen loss from toluene molecular ions takes place as if all eight positions within these ions were equivalent, and this has been interpreted in terms of complete hydrogen scrambling prior to dissociation. [57] The extent of isomerization becomes apparent from the close similarity of the toluene and cycloheptatriene El mass spectra... 

Figure 10-24 shows the reaction of a secondary amine with a ketone to form an encimine. With the exception of the last step, the mechanism for the formation of an enamine is similar to both the mechanism for the formation of a hemiacetal/acetal and the mechanism for the formation of an imine. In this case, because losing a hydrogen ion from a Ccirbon adjacent to the C=N carbon occurs more easily than a second attack, an enamine forms. The hydrogen loss is on the side that yields the more stable alkene. 

All 60 C-atoms of Cjq are incorporated in the CgoHjo polycyclic aromatic hydrocarbon (PAH) 6, for which an efficient synthesis was developed [153], Laser irradiation of 6 at 337 nm induces hydrogen loss and the formation of CgQ, as detected by mass spectrometry (Scheme 1.6). Control experiments with C-labeled material and with the C48H24 homologue of 6 verified that the C50 is formed by a molecular transformation directly from the C50H30 PAH and not by fragmentation and recombination in the gas phase. 

A single crystal l-methyluracil 9-ethyladenine complex was investigated using EPR, ENDOR and FSE.25 Samples were x-irradiated and spectra taken at 10 K. This work is a reinvestigation of a system that had been studied using EPR only after irradiation at 295 K.26 Three radicals were identified in 1-methyluracil, the net methyl-hydrogen-loss radical (31), (see p. 258) the anion radical (32), and the... 

Under certain conditions, platinum alkene complexes can be converted to jr-allyl complexes by hydrogen loss (equation 281).860 Allyl alcohol insertion into a platinum(II) carbonyl bond gives an allyloxycarbonylplatinum(II) intermediate which can be decarboxylated to form the jj3-allyl complex (equation 282).861,863... 

Oxygen content, 0.08% max, detd in accord-with ASTM procedure El 59 (Hydrogen Loss of... 

Experiments with deuterated species show extensive H/D scrambling, which implies longer-lived intermediates in the reaction. Calculations at the B3LYP/6-311+G(2d,p) level suggest that the reaction pathway involves bond formation between the cycloheptatrienylidene dication and acetylene, followed by isomerization and hydrogen loss (Scheme 9). The authors of this study note the possibility of similar chemistry generating polycyclic aromatic compounds in interstellar space. 

TABLE 6. Calculated reaction energies and ZPE corrections (kcalmol 1) for hydrogen loss from EH4 and H3ECH3 ... 

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