Labelling exchange

In early 1993, Haw and co-workers (107) reported in situ studies of allyl alcohol-/-13C on HZSM-5 and CsHX. No persistent carbenium ions were observed, but 1,3 label exchange was observed for the alcohol on the weakly acidic zeolite. We interpreted this as support for a transient allyl cation. The low stability of this cation was invoked to explain the failure to observe this species as a persistent species. Downfield signals observed in that study were attributed to the formation of propanal. Later in 1993, Biaglow, Gorte, and White (BGW) (108) reported similar studies conducted at different loadings and assigned a downfield resonance (variously reported at 216 and 218 ppm by BGW) to the allyl cation in HZSM-5. 

As in Section 4.1, it is convenient to label exchanging ions with numerical indices in describing multicomponent ion exchange equilibria. The thermodynamic approach will be illustrated for a ternary cation exchange system (e.g., Na+, Mg2+, Ca2+), but the extension to an N-ary system is direct. This is evident, for example, in the Gibbs-Duhem equation for a ternary system ... 

Schleyer and coworkers investigated the nature of the 9-barbaralyl cation by solvolysis studies of the corresponding tosylate. The acetolysis of 9-deuterio-9-barbaralyl tosylate gave 9-barbaralyl acetate with complete deuterium scrambling, whereas solvolysis in more nucleophilic aqueous acetone gave the product alcohols with the label exchanged to only positions C3, C7 and C9 (equation 50). Solvolysis of 4-deuteriobicyclo[3.2.2]nona-2,6,8-trien-4-yl 3,5-dinitrobenzoate also resulted in the formation of the 9-barbaralols with deuterium scrambled to positions 1, 2, 8, 4, 5 and 6, with only trace amounts at C3 and (equation 51). 

The formalism necessary to calculate ESR spectra that arise from collisional exchange interaction is outlined briefly, and detailed equations used in our calculation are given. A simple but naive model for the collision frequency and its connection to the spin label, exchange collision frequency is developed. The model is instructive and indicates the limit of sensitivity of the spin label method in measuring surface viscosities. 

H resonance from 4.3 to 5.1 ppm. At 293 K and above, label exchange between the Bronsted sites and benzene occurred at a measurable rate, and a H signal for the former grew in at 7.5 ppm at the expense of the signal from the latter. 

CsHX. Label exchange between the I (64 ppm) and 3(115 ppm) positions were observed as well as the formation of allyl ether (72 ppm). 

Label exchange in the bissulfinate. The possibility of oxygen atom... 

For example, for bound states, all solutions other than those of class Q (see p. 895) must be rejected. In addition, these solutions if/, which do not exhibit the proper symmetry, even if i/rp does, have also to be rejected. They are called mathematical (non-physical) solutions to the Schrodinger equation. Sometimes such mathematical solutions correspond to a lower energy than any physically acceptable energy (known as underground states). In particular, such illegal, non-acceptable functions are asymmetric with respect to the label exchange for electrons (e.g., symmetric for some pairs and antisymmetric for others). Also, a fully symmetric function would also be such a non-physical (purely mathematical) solution. 

Indicate whether each of the following functions is symmetric, antisymmetric, or neither with respect to operation by the label exchange operator Pii-... 

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