Observational Results

Figure B 1.16.9 shows background-free, pseudo-steady-state CIDNP spectra of the photoreaction of triethylamine with (a) anthroquinone as sensitizer and (b) and (c) xanthone as sensitizer. Details of the pseudo-steady-state CIDNP method are given elsewhere [22]. In trace (a), no signals from the p protons of products 1 (recombination) or 2 (escape) are observed, indicating that the products observed result from the radical ion pair. Traces (b) and (c) illustrate a usefiil feature of pulsed CIDNP net and multiplet effects may be separated on the basis of their radiofrequency (RF) pulse tip angle dependence [21]. Net effects are shown in trace (b) while multiplet effects can...

In all other cases the observed result will depend upon both the speed of mixing and the speed of nitration. The relative rate will be greater than unity by an amount peculiar to the conditions of the experiment. Again, if the alkylbenzene is sufficiently reactive to be nitrated upon encounter, whilst benzene is not, the relative rate will be greater than unity and, for the experimental conditions, will be a limiting upper value no matter what aromatic is used. 

Again the uncertainty about the proportion of an observed result which is due to nitration and the proportion which is due to nitrosation exists. Thus, in expt. 11 phenol was being nitrated above the encounter rate and the observed isomer distribution could arise from a combination of nitration by whatever is the usual electrophile with nitration by a new, less reactive electrophile, or with nitrosation, or all three processes could be at work. 

When this stereoelectronic requirement is combined with a calculation of the steric and angle strain imposed on the transition state, as determined by MM-type calculations, preferences for the exo versus endo modes of cyclization are predicted to be as summarized in Table 12.3. The observed results show the expected qualitative trend. The observed preferences for ring formation are 5 > 6, 6 > 7, and 8 > 7, in agreement with the calculated preferences. The relationship only holds for terminal double bonds. An additional alkyl substituent at either end of the double bond reduces the relative reactivity as a result of a steric effect. 

While at high densities we observe perfect exponential scaling of p x), at lower dilute densities (with sufficiently long chains ) one observes results consistent with Eq. (16b). The insert in Fig. 5 shows that the MWD at dilute densities agrees with the additional power-law dependence p x) oc in the limit of small x, confirming the theoretical predictions [33,34]. 

Flame acceleration does not generate extremely high overpressures. That is, numerical simulation of an explosion process with a steady flame speed equal to the highest flame speed observed results in a conservative estimate of its blast effects. 

The survey method relies heavily on interviews to gather data and typically involves little or no on-site verification or observation. Results can be obtained in a timely and cost-effective mannen however they may reflect the bias of the individual filling out a self-administered questionnaire. 

Tire heats of formation of the intermediate methylamino-transition states of the SnFI methylamination reaction of these nitro-1,8-naphthyridines were calculated by the PM3 method. Tire agreement between the calculated and observed results was found to be satisfactory (97LAR2601,97MI4). 

Once such effects had been noted, it became necessary to interpret the observed results and to classify the solvents. The earliest attempts at this were by Stobbe, who reviewed the effects of solvents on keto-enol tautomers [4]. Since then many attempts have been used to explain solvent effects, some based on observations of chemical reactions, others on physical properties of the solvents, and yet others on spectroscopic probes. All of these have their advantages and disadvantages and no one approach can be thought of as exclusively right . This review is organized by type of measurement, and the available information is then summarized at the end. 

Two Cells Placed Back to Back. In Sec. 57 of Chapter 6 we discussed the e.m.f. of two cells placed back to back. Both cells contained the same solute in aqueous solution, but at different concentrations. We saw that, when a current flows, the net result is simply to transfer an amount of solute from one solution to the other. Hence the observed resultant e.m.f. of the pair of cells is a measure of the change in free energy on transferring a pair of ions from one solution to the other in fact, this change of free energy expressed in electron-volts is numerically equal to the e.m.f. expressed in volts. 

Problem 24.24 Indole reacts with electrophiles at C3 rather than at C2. Draw resonance forms of the intermediate cations resulting from reaction at C2 and C3, and explain the observed results. 

CycIopentadiene reacts with cycloheptatrienone to give the product shown. Tell what kind of reaction is involved, and explain the observed result. Is the reaction suprafacial or antarafacial ... 

The cyclohexadecaoctaene shown isomerizes to two different isomers, depending on reaction conditions Explain the observed results, and indicate whether each reaction is conrotatory or disrotatory. 

The following thermal rearrangement involves two pericyclic reactions in sequence. Identify them, and propose a mechanism to account for the observed result. 

The following rearrangement was devised and carried out to prove the stereochemistry of [1,5] sigmatropic hydrogen shifts. Explain how the observed result confirms the predictions of orbital symmetry. 

The relative error is the absolute error divided by the true value it is usually expressed in terms of percentage or in parts per thousand. The true or absolute value of a quantity cannot be established experimentally, so that the observed result must be compared with the most probable value. With pure substances the quantity will ultimately depend upon the relative atomic mass of the constituent elements. Determinations of the relative atomic mass have been made with the utmost care, and the accuracy obtained usually far exceeds that attained in ordinary quantitative analysis the analyst must accordingly accept their reliability. With natural or industrial products, we must accept provisionally the results obtained by analysts of repute using carefully tested methods. If several analysts determine the same constituent in the same sample by different methods, the most probable value, which is usually the average, can be deduced from their results. In both cases, the establishment of the most probable value involves the application of statistical methods and the concept of precision. 

If the reaction time for the TBDMS derivatives is not long enough, a mixture of mono- and di-TBDMS derivatives is observed, resulting in more than one GC peak and thus reduced sensitivity. 

Various factors involved in both steps have been considered explicitly by Friedman and colleagues (29, 47, 49, 54, 67) to rationalize isotope effects in these reactions. Their treatment involves orientation effects, displacement isotope effects, and dissociation isotope effects in order to account for observed results. Stevenson and Schachtschneider (59) have also presented a treatment of decomposition isotope effects. 

Cieplak apphed this effect to the explanation of the shift of selectivity in the reactions of the pentamethylcyclopentadienes 21,19, and 20 having substiments of formyl, vinyl, and (hydroxyimino)methyl moiety at the 5-positions [14]. He pointed out that the observed result is consistent with the notion that in the case of formyl moiety the hyperconjugative effect is enhanced by lone pair back-donation due to ... 

The value given in Table II for adrenals 21 days following administration suggests that this tissue may concentrate TCDD- C and/or a metabolite. This observation results probably from experimental error. The disintegrations per minute (dpm) above background for this tissue were only 17, 29, and 90. Since the total amount of tissue available for analysis was less than 20 mg, the multiplication factor may have magnified the error many fold. 

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