Visible-ultraviolet spectra

With few exceptions, 1,2-dioxetanes are yellow. They exhibit a A u at about 280 nm, with low extinction coefficients (e 20).llb-12 The origin of this band is still not certain, but it most likely corresponds to the excitation of the oxygen-oxygen bond, as suggested by theoretical work108 and photon-electron spectra.46 The yellow color is due to tail-end absorption even out to 4S0 nm. One of the exceptions is the diadamantylidene-l,2-dioxetane (Iz), which is white and has its Am at 265 nm (e = 21.5).38 

As pointed out already, one of the most characteristic properties of the four-membered ring cyclic peroxides is their ability to chemiluminesce on thermal decay into carbonyl products [Eq. (14)1. 

The light emission, which ranges at about 420 10 nm, corresponds to the fluorescence of the carbonyl product.,b Ub l2 , 4b 37,38 Intriguing is the tetramethyl system (lb), which exhibits emission at 400 nm in non-degassed and at 430 nm in degassed solutions of acetonitrile. The former has been attributed to fluorescence, the latter to phosphorescence.1 lb 47 

Although an attempt was made to obtain a PE spectrum of the diadamantylidene dioxetane (lz),48 it decomposed. However, recently Brown46 reported the PE spectrum of the 1,2-dioxetane (lb). It exhibits vertical ionization potentials at 8.98, 10.94, 11.41, and 12.09 eV. The first IP was assigned to ionization from the n level of the peroxide linkage of lb, thus corroborating the UV-visible and fluorescence spectra. 

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CIO4 and on [Co2(CNR),oI](C104)3 (R = CH3, CjHj) has been reported (28). The proposed structure for the latter complex, involving a linear Co—I—Co group, is supported by these data. The ultraviolet-visible spectra for [Co(CNCH3)5]C104 has been studied (51). The crystal structure determination of tra i-Co(CNC H4CH3)4l2 has been completed (58). 

A report by Ozin et al. in 1977 describes the formation of Ti(CO)6 via matrix cocondensation techniques (11). This green complex, while not isolated, was characterized by its infrared and ultraviolet-visible spectra. In a pure CO matrix, a color change from green to reddish-brown was observed on warming from 10 K to about 40-50 K. The infrared spectrum of the reddish-brown material showed no evidence for coordinated CO, thus suggesting the extreme thermal instability of Ti(CO)6. 

When the coulometric detector was turned on, both leuco forms were completely oxidized to their nonfluorescing chromatic forms and thus vanished from the fluorescence channel. This disappearance was balanced by the arrearance of their chromatic forms in the diode array channel. The confirmation of malachite green, gentian violet, and tlieir leuco analogs in catfish and trout tissue could be based, therefore, on the correct retention times, the observation of the natural fluorescence of the leuco forms when the coulometric detector was turned off, the absence of the leuco form peaks in the 588 nm channel when the coulometric detector was off, the disappearance of the fluorescence of the leuco forms when the coulometric detector was on, the appearance of peaks of parent drugs formed by oxidation of the leuco forms in tlie. S88-nm diode array channel, and the correct ultraviolet-visible spectra maxima for all four peaks. 

Table 2 Ultraviolet-Visible Spectra of Some A,B-Diheteropentalenes...

Collections of spectroscopic data (a) Standard Spectra Collection. Sadtler Research Laboratories, Philadelphia. (The 1980 index covers 48 000 grating i.r. spectra, 59000 prism i.r. spectra, 48 000 ultraviolet/visible spectra, 32 000 60 MHz n.m.r. spectra, and 7000 carbon-13 n.m.r. spectra.)... 

Fourage, L., Helbert, M., Nicolet, P., and Colas, B. (1999). Temperature dependence of the ultraviolet-visible spectra of ionized and un-ionized forms of nitrophenol consequence for the determination of enzymatic activities using nitrophenyl derivatives—A warning. Anal. Biochem. 270,184. 

Retcofsky, H. L., Friedel, R. A. Spectra of coals and coal extracts. — Ultraviolet-visible spectra of carbon disulfide extracts, in Spectrometry of Fuels (ed. Friedel, R. A.) p. 37, New York—London, Plenum Press 1970... 

These methods of obtaining complete ultraviolet-visible spectra can be very time-consuming. However, rapid scanning spectrophotometers based on optical diode array detectors are now eormnereially available and are capable of recording complete spectra in very short time intervals (1 second or less). They can therefore be used to obtain spectra of separated components without stopping eluent flow or to detect at several wavelengths simultaneously. 

The lanthanide complexes lack distinct ultraviolet-visible spectra and, hence, kinetic information on their complex formation and dissociation reactions was obtained indirectly by the metallochromic indicator method [9]. These studies indicate that in the case of the Cyanex 272 complexes, the CPC efficiencies are mainly limited by the slow dissociation of the M(HL2)HL+ complex at the heptane-H20 interface. 

Fig. 1. Comparative ultraviolet-visible spectra of Cfto and Ph2Cfti (labeled C i ). The inset is the 700- to 350-nm region at 20 times the gain. The absorbance of two spectra has not been normalized.

Sodium azide, manufacture of 48H-490 Solvent effete on ultraviolet-visible spectra 73... 

A set of four pure-component ultraviolet-visible spectra, each containing 76 data points, was taken firom reference 18 representing a K-matrix calibration situation and is referred to as the UVl data set (see Figure 2). To limit the discussion, results for subsets with 5 wavelengths are reported. From enumerating searches, i.e., checking all possible wavelength combinations, the best subsets are known for... 

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