Beta loss transition

The thermal transitions of the manganese dioxides can be iUustrated by the beta phase which undergoes successive reductions and corresponding loss of oxygen as the temperature is increased (49). 

Although the loss of beta hydrogens should decrease the stability of a carbonium ion or its related transition states, if enough of the beta... 

A nucleus that has an excess of neutrons will undergo neutron to proton transition, a process that may restore the N P ratio but that requires the loss of an electron to convert the neutron to a positively charged proton, and as a result the atomic number increases by one. The particle emitted is a high speed electron known as a negation (P ) and the atom is said to emit beta radiation, e.g. 

The increased ionic freedom between the propagating polymer ion and its gegen ion occurs concurrently with increased space separation between the two ion species. The studies of Schuerch and co-workers and of Yoshino and co-workers (98) with deuterated acrylates and by Natta and co-workers (99) with sorbic esters show that this increased separation allows trans addition to mono olefins and 1,4 trans addition to conjugated dienes before complete loss of isotactic steric control at the end of the chain. The increased freedom between the propagating ion and the less closely associated gegen ion appears to result in a distortion of the cyclic transition state which permits backside attack at the beta position of the incoming acrylate monomer and 1,4 attack on the incoming sorbate monomer. 

There are two types of flow nozzles. The common nozzle used in the United States is the so-called long-radius, or ASME flow nozzle. This nozzle comes in two versions, known as low-beta-ratio and high-beta-ratio designs. Flow nozzles represent a transition between orifices and flow tubes. At the same pressure drop, they pass about 60% more flow than an orifice. They are more compact and less expensive, but they also produce more head loss than do flow tubes. 

Another possible mechanism for the final step has been proposed. This requires a beta hydride shift from the hydroxyl bearing carbon to the alpha carbon with loss of PdCli- This mechanism cannot be ruled out at this time, but the first suggestion seems more consistent with the known chemistry of the transition metals. 

The volumetric, elastic and dynamic properties of internally and externally plasticised PVC were studied and compared with those of unplasticised PVC. The glass transition temperature for the plasticised samples was markedly lowered and this decrease was more important for the externally plasticised ones. The positions of the loss peaks from dielectric alpha-relaxation measurements confirmed the higher efficiency of the external plasticisation. However, the shape of the dielectric alpha-relaxation function was altered only for the internally plasticised samples. The plasticisation effect was linked with a decrease in the intensity of the beta-relaxation process but no important changes in the activation energy of this process were observed. The results were discussed. 47 refs. 

Figure 5. Polysulfone beta transition s dielectric loss as a function of unassociated...

Figure 9. PVAc dielectric beta transition loss maxima vs 1/T as a function of...

A number of kinetic isotope studies have been reported for gas-phase eliminations. Isopropyl bromide-dg decomposes more slowly than isopropyl bromide and the intramolecular isotope effects (A ,c2D4hx-c2D4)/ (C2D4hx-c2D.iH)) have been recorded for pyrolyses of ethyl acetate (2.0), chloride (2.20), and bromide (2.10) at 500°C. At the elevated reaction temperatures, these values correspond to the maximum predicted for complete loss of the C-H stretching vibration and they have been interpreted as indicating considerable weakening of the C-H bond in the transition state. Whether this is a homolytic or hetero-lytic bond fission, it is remarkably insensitive to beta substituent effects on rate. The intramolecular isotope effects in these cases could reflect predominantly a secondary isotope effect rather than the intended primary effect and dissection into an intermolecular and secondary isotope effect would prove more fruitful. (Section 2.2.1.)... 

In the dynamic mechanical loss spectra of polymers, the transitions that are related to different molecular motions within polymers are called alpha, beta, and gamma transitions. 

Figure 13.5 compares the loss moduli (damping) of linear (high-density) and branched (low-density) polyethylene. Three transitions are seen alpha at 80 C, beta at -5 C, and gamma at -110 "C. Each of these transitions corresponds to specific molecular motions which have significance in terms of structure-property relationships ... 

Figures 13.6(a) and (b) show the alpha and beta transitions obtained in dielectric thermal analysis of PET. The alpha transition (Tg) is affected by the large-scale micro-Brownian motion in the amorphous (non-crystalline) phase. The Brownian motion is observed as a peak in the 1 Hz loss factor cnrve at about 90 °C. The beta transition is considered to be a resnlt of main-chain motion involving the ester groups.

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