Spectroscopic observables

Three are the spectroscopic observables routinely collected for any compound with fully automatic experimental devices, i) vibrational frequencies, 9 (cm 1 eV= 8065 cm ) or peak frequencies, ii) 

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It should be emphasized that isomerization is by no means the only process involving chemical reactions in which spectroscopy plays a key role as an experimental probe. A very exciting topic of recent interest is the observation and computation [73, 74] of the spectral properties of the transition state [6]—catching a molecule in the act as it passes the point of no return from reactants to products. Furthennore, it has been discovered from spectroscopic observation [75] that molecules can have motions that are stable for long times even above the barrier to reaction. 

Bausch J W, Prakash G K S, Olah G A, Tse D S, Lorents D C, Bae Y K and Malhotra R 1991 Considered novel aromatic systems. 11. Diamagnetic polyanions of the Cgg and C g fullerenes. preparation, 13-C and 7-Li NMR spectroscopic observation, and alkylation with methyliodide to polymethylated fullerenes J. Am. 

The vast majority of single-molecule optical experiments employ one-photon excited spontaneous fluorescence as the spectroscopic observable because of its relative simplicity and inlierently high sensitivity. Many molecules fluoresce with quantum yields near unity, and spontaneous fluorescence lifetimes for chromophores with large oscillator strengths are a few nanoseconds, implying that with a sufficiently intense excitation source a single... 

Basche T, Kummer S and Brauchle C 1995 Direct spectroscopic observation of quantum ]umps of a single molecule Nature 373 132-4... 

The mechanism of the Fischer cyclization outlined in equation 7.1 has been supported by spectroscopic observation of various intermediates[4] and by isolation of examples of intermediates in specialized structures[5]. In particular, it has been possible to isolate enehydrazines under neutral conditions and to demonstrate their conversion to indoles under the influence of acid cata-lysts[6]. 

Steric effects of the substituents in positions 4 and 5 cannot shift the protomeric equilibrium sufficiently to permit spectroscopic observation of the thiol form (43b) ultraviolet spectra of 4-terr-butyl-5-methyl-A-4-thia2oline-2-thione (49a) in neutral solvents do not reveal any trace of the thiol protomer (49bi (Scheme 21) (70). 

We may now be on the verge of the third phase of oxirene chemistry in which modern matrix isolation techniques (80CSR1) will permit the spectroscopic observation of this system, theory will serve as a guide to the synthesis of relatively stable oxirenes (c/. a fairly stable... 

Pyridine is more nucleophilic than an alcohol toward the carbonyl center of an acyl chloride. The product that results, an acylpyridinium ion, is, in turn, more reactive toward an alcohol than the original acyl chloride. The conditions required for nucleophilic catalysis therefore exist, and acylation of the alcohol by acyl chloride is faster in the presence of pyridine than in its absence. Among the evidence that supports this mechanism is spectroscopic observation of the acetylpyridinium ion. An even more effective catalyst is 4-dimeftiyIaminopyridine (DMAP), which functions in the same wsy but is more reactive because of the electron-donating dimethylamino substituent. ... 

Among the newer probes now being developed, spectroscopic observations of crystals in the elastic-plastic regime hold promise for limited development of atomic level physical descriptions of local defects [91S02]. It is yet to be determined how generally this probe can be applied to solids. The electrochemical probe appears to have considerable potential to describe shock-compressed matter from a radically different perspective. 

Presence and nature of intermediates. Demonstration of an intermediate shows that a reaction is complex. An intermediate may be sufficiently stable to isolate, but more commonly it can only be detected by physical means (such as some form of spectroscopic observation) or by indirect chemical means ( trapping it in a side reaction). Despite the instability of some intermediates, these are ordinary chemical species whose properties can, in principle at least, be determined experimentally. 

Spektralanalyse, /. spectrum analysis, spektralanalytisch, a. spectroscopic, spectro-metric. — adv. by spectrum analysis. Spektral-apparat, to. spectroscopic apparatus, -beobachtung, /. spectroscopic observation, -bereich, -bezirk, to. spectral region, -farbe, /. spectral color, spectrum color, -gegend, /. spectral region, -lampe, /. spectrum lamp, -hnie, /. spectrum line, spectral line, -probe, /. spectrum test, -rohr, n.. -rohre, /. spectrum tube, spectral tube, -tafel, /. spectrum chart, spectral chart. 

Through spectroscopic observations and sometimes tenuous deductions there has accumulated a significant picture of the makeup of the planetary atmospheres. Doubt pervades much of this picture, yet it represents our starting place in knowledge as we venture outside our own atmosphere for the first time. Table 25-V summarizes a part of this information—the maximum surface temperatures and the chemical compositions. Naturally, these compositions are incomplete ... 

Step 1. Estimate the concentration of the element from a chart recording of the sample or by optical spectroscopic observation. 

It should be emphasized that, in contrast to the cases of secondary alkyl cations (Olah et al., 1964 Saunders et al., 1968) and tertiary alkyl cations (Olah et al., 1964 Brouwer and Mackor, 1964), the evidence for the existence of primary alkyl cations as distinct species has been only indirect, because they have escaped direct spectroscopic observation so far. 

A partially oriented (using polarized, visible photolysis) sample of Fe(CO)s in solid CO at 20 K has been prepared (193). It was subsequently found that no change in the polarization properties of the system occurred during several hours of spectroscopic observation. It was concluded that the fluxionality of Fe(CO)5 had been quenched under these conditions, as, were this not the case, maintenance of polarization for more than a fraction of a second would be impossible. 

The H-NMR and C-NMR chemical shifts have been assigned and substractures have been deduced on the basis of COSY-45° (Problem 5.13) and other spectroscopic observations. Interpret the HMBC spectrum and identify the heteronuclear long-range coupling interactions between the H and C nuclei. 

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