H transfer

The transformation of ethylene to the carbene requires the re-pairing of three electron pairs. It is a phase-preserving reaction, so that the loop is an ip one. The sp -hybridized carbon atom formed upon H transfer is a chiral center consequently, there are two equivalent loops, and thus conical intersections, leading to two enantiomers. 

H transfer from the methyl to the exocyclic nitrogen of the acetamido group. 

An example of proton (H ) transfer from a protonated solvent molecule (SH ) or cluster to form a quasi-molecular ion (MH ) of the substrate (M). 

Fourier s Law of Heat Conduction. The heat-transfer rate,, per unit area,, in units of W/m (Btu/(ft -h)) transferred by conduction is directly proportional to the normal temperature gradient ... 

Upon exposure to uv light, ground-state benzophenone is excited to the ttiplet state (a diradical) which abstracts an alpha H atom from the alcohol, resulting in the formation of two separate initiating radicals. With amine H atom donors, an electron transfer may precede the H-transfer, as in ttiplet exciplex formation between benzophenone and amine (eq. 43) ... 

Coke deposition is essentially independent of space velocity. These observations, which were developed from the study of amorphous catalysts during the early days of catalytic cracking (11), stiU characteri2e the coking of modem day 2eohte FCC catalysts over a wide range of hydrogen-transfer (H-transfer) capabihties. 

FIG. 23-8 Diagrams of a composite process (a) process flow diagram, (h) transfer function diagram. The overall transfer function is ... 

H transfer between two very unequally populated tautomers... 

Much more complicated is the course of the reaction if the oxazirane is derived instead of from benzaldehyde from an aliphatic ketone. Here the possibility of an H-transfer does not occur. Further complications are found if the A -alkyl group can be attacked by the radicals. 

Oxaziranes derived from isobutyraldehyde react with ferrous salts to give only substituted formamides fEq. (23)], The chain propagating radical 30 thus suffers fission with elimination of the isopropyl group. An H-transfer would lead to substituted butyramides, which are not found. Here is seen a parallel to the fragmentation of alkoxyl radicals, where the elimination of an alkyl group is also favored over hydrogen. The formulation of the oxazirane fission by a radical mechanism is thus supported. 

Slow double-bond shifts and little skeletal isomerization H-transfer is minor and nonselective for tertiary olefins only small amounts of aromatics formed from aliphatics at 932°F (500°C)... 

Rapid double-bond shifts, extensive skeletal isomerization, H-transfer is major and selective for tertiary olefins large amounts of aromatics formed from aliphatics at 932°F (50t) O... 

Garner, F.H. andKEEY, R.B. Chem. Eng. Sci. 9 (1959) 218. Mass transfer from single solid spheres — H. Transfer in free convection. 

When the product ion moved with a higher kinetic energy than predicted by the stripping model, the collision apparently was more elastic— i.e., less kinetic energy of the incident ion was used for internal excitation of the products. In an ideal elastic collision with H transfer the products carry no internal energy at all. If the secondary ion moves forward and the H atom moves backwards, conservation of momentum requires that the primary ion has a velocity ... 

The above discussion has been concerned with H transfer reactions to alkyl ions. In addition, there is mass spectrometric (16) and radiolytic (18) evidence that H can also be transferred to smaller olefinic ions (CnHm +)... 

When both reactants have comparable ionization potentials, there is a close relationship between the H2 and H2 transfer reactions. For instance, a low efficiency of the H. transfer reaction from the alkane to a neutral olefin molecule (at least in the case of cyclohexane) is paralleled by a low efficiency of the corresponding H2 transfer process. Such a relationship can be accounted for by resonance phenomena. Unfortunately, not enough information is available on those systems where the... 

In contrast, for R = C6H3Pr2-2,6, H transfer and an unusual coupling of two Pr methine C atoms resulted in a linked formamidinate complex as illustrated in Scheme 193. °° ... 

The reactivity shown in Scheme 3 results from the low bond dissociation energy (BDE) of the P-H bond [11] k=l.2 10 M s for the H-transfer from R02P(0)H to a primary C-centered radical) and the fast halogen-atom transfer from a C-halogen bond to a phosphonyl radical [9,12] (fc=4 10 M s for f-Bu-Br and k=83 10 M s for Cl3C-Br). Piettre et al. [13] pointed out that these chain reactions were even more efficient when dialkylthiophosphites and the corresponding dialkylphosphinothioyl radicals were involved. 

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