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Hydrogen scrambling

A book (B-71MS) and a review by Nishiwaki (74H(2)473) contain much information about the behaviour of pyrazoles under electron impact. The Nishiwaki review covers mainly the hydrogen scramblings and the skeletal rearrangements which occur. One of the first conclusions reached was that pyrazoles, due to their aromatic character, are extremely stable under electron impact (67ZOR1540). In the dissociative ionization of pyrazole itself, the molecular ion contributes about 45% to the total ion current thus, the molecular ion is the most intense ion in the spectrum. [Pg.202]

Another interesting fact is that hydrogen scrambling, i.e. randomization of the ring hydrogens of pyrazole to lose positional identity on electron impact, has not been observed to any significant extent (see however 780MS575). [Pg.202]

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... [Pg.252]

Cooks, R.G. Howe, I. Tam, S.W. Williams, D.H. Studies in Mass Spectrometry. XXIX. Hydrogen Scrambling in Some Bi-cyclic Aromatic Systems. Randomization Over Two Rings. J. Am. Chem. Soc. 1968, 90,4064-4069. [Pg.323]

Table 3. Relative Energies (in kcal mol ) of the CHj Transition Structures for Hydrogen Scrambling, 2 and 3 (A = C), Relative to 1 (Energetic Reference Point) at Different Levels of Theory. Table 3. Relative Energies (in kcal mol ) of the CHj Transition Structures for Hydrogen Scrambling, 2 and 3 (A = C), Relative to 1 (Energetic Reference Point) at Different Levels of Theory.
To judge whether dihydrogen attachment would increase the barrier for complete hydrogen scrambling, we also examined structures that contain the 2v isomer of... [Pg.136]

As expected, AlHj behaves very similarly, but it is even less stable [Z)q = 0.1 kcal mor, TZ2P CCSD(T) + ZPVE]. Here also, only the free rotation of the dihydrogen moiety occurs with no barrier, and total hydrogen scrambling via 3 (A=Al) is very unlikely (25.5 kcal mol" ). However, the structure 4 (A=Al) remains stable... [Pg.154]

Internal hydrogen scrambling and isotope redistribution between propane and solid catalysts may proceed by a rather complex mechanism involving several pathways with different rates and activation energies. The competitive pathways cannot be distinguished if the temperature for activating propane on zeolites is... [Pg.184]

Fig. 22. Selective hydrogen mixing between C2H4 and C2D4 during induction time Tor the isomerization of m-2-butene-d0, and superimposed hydrogen scrambling between C2D4 and cis-2-butene-dQ after the induction time on cut single crystal catalyst of MoS2 at 100°C (8,14). Fig. 22. Selective hydrogen mixing between C2H4 and C2D4 during induction time Tor the isomerization of m-2-butene-d0, and superimposed hydrogen scrambling between C2D4 and cis-2-butene-dQ after the induction time on cut single crystal catalyst of MoS2 at 100°C (8,14).
The rearrangements of several twistane derivatives to adamantyl cations under the same conditions, on the other hand, appear to involve reversible, random carbonium ion formation, at least to a limited extent. Rearrangement of 2-twistanol-2-d (38) occurs with considerable intermolecular hydrogen scrambling (Eq. (15)) 40T Similar intermolecular rearrangements are observed when a 50 50 mixture of 1-adamantanol and l-adamantanol-3,5,7-d3 in S02 is treated with SbFs 40). [Pg.20]

The conversion is completely reversible by removing the H2 gas from solution and is remarkably sensitive to phosphine size and ion-pairing effects. Equation (14) is facilitated by hydrogen bonding interactions, e.g., Eq. (15) where the OH and IrH hydrogens scramble via rotation of the H2 ligand. [Pg.142]


See other pages where Hydrogen scrambling is mentioned: [Pg.102]    [Pg.27]    [Pg.142]    [Pg.266]    [Pg.12]    [Pg.13]    [Pg.18]    [Pg.19]    [Pg.21]    [Pg.24]    [Pg.275]    [Pg.318]    [Pg.126]    [Pg.127]    [Pg.135]    [Pg.140]    [Pg.143]    [Pg.148]    [Pg.149]    [Pg.157]    [Pg.752]    [Pg.583]    [Pg.115]    [Pg.61]    [Pg.115]    [Pg.116]    [Pg.102]    [Pg.112]    [Pg.120]    [Pg.208]    [Pg.208]    [Pg.209]    [Pg.210]    [Pg.215]    [Pg.216]    [Pg.87]    [Pg.141]   
See also in sourсe #XX -- [ Pg.17 , Pg.18 ]

See also in sourсe #XX -- [ Pg.204 ]

See also in sourсe #XX -- [ Pg.17 , Pg.18 ]

See also in sourсe #XX -- [ Pg.17 , Pg.18 ]

See also in sourсe #XX -- [ Pg.159 , Pg.161 ]

See also in sourсe #XX -- [ Pg.2 , Pg.2 , Pg.5 , Pg.5 , Pg.5 , Pg.5 , Pg.334 ]




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Scrambling

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