Alcohols absorption coefficients

The first feature of interest is the variation of the peak height of the 3630 cm "3 (monomer) band with temperature and with concentration. Fig. 3 shows the apparent absorption coefficient, em, of the monomer band in ethanol as a function of concentration at several temperatures. The general decrease of em with increasing concentration is, of course, the result of depletion of monomer by formation of H-bonded species. Tt should be noted that the intercepts at zero concentration vary with temperature, with the highest value coming at the lowrest temperature. We reported this effect previously [10] and attributed it to interaction between alcohol monomers and the 0014 solvent, probably similar to weak H-bonding. Others have also noted this effect [11]. 

Cm, Xd> Xm arc concentrations and mole fractions, respectively, of dimer and monomer em° is the absorption coefficient of the monomer (found by extrapolating em to C=0 and Kx KC for Cd4. We found values of K for each of the alcohols at a series of temperatures from —10° to +45°C. A plot of log10 K vs. IjT is given in Fig. 4. There is considerable scatter, but the trend in each case is roughly linear, within the limits of error. From the slopes of the lines the heats of formation of the alcohol dimers were calculated and are listed in Table 1. 

Several reductive assays have been proposed (Table 3). A test using reduction of l,l-diphenyl-2-picrazyl (DPPH) radical was introduced in the 1950s (B15) and has been used by various authors. DPPH is a stable free radical, which can be bought in substantia. It has an absorbance maximum at 515 nm (millimolar absorption coefficient e = 12.5 mM-1 cur1) (A15). A disadvantage of this chromogen lies in the fact that it can be dissolved only in organic (especially alcoholic) but not in aqueous media, which limits its use for studies of hydrophilic antioxidants. Reduction of ABTS also can be followed by electron spin resonance (ESR) (Yl). 

Figure 40. Dependence of ota/v2 (where aa is the amplitude absorption coefficient and v the frequency of the sound wave) on mole fraction of t-butyl alcohol in aqueous mixtures at 70 MHz and 298 K.

The t-butanol/hydrocarbon system has attracted more Interest (135,82,83). As has been shown above neat t-butanol in its photolysis differs markedly from the primary and secondary alcohols in that the formation of hydrogen is not the major process. Rather, it is the scission of the C-C bond. On dilution with a hydrocarbon solvent, however, <(i(H2) increases and < )(CH ) (which is an approximate measure for the C-C split) decreases strongly (82). More detailed studies have been undertaken in dilute solutions (0.04 to 1.15 mol/1) (83) in order to try and correlate the photolytic behavior of t-butanol, and the marked change in the absorption coefficient of t-butanol with dilution, and its state of aggregation in the hydrocarbon solvent. It is known that t-butanol forms various aggregates, but opinions as to their structure often differ for example, trimer (170) or tetramer (171) species are considered to predominate if concentrations are not too low. 

The fluorescence of SAA is roughly a mirror image of the absorption of the cis-qulnold isomer (Table 7). Minor blue shifts have been observed if the hydrocarbon solvent is replaced by an alcoholic solvent, but the evidence is not sufficient to permit postulating an n—it fluorescent state (53). Evidence of the tt-tt character of the emitting state is the high absorption coefficient of the quinoid form of the order of e = 10. Furthermore, fluorescence from n-TT levels of ketonlc compounds is unusual. The fluorescence decay time has been measured to be xp = 20 10 ns... 

Figure 2 (A) UV spectrum of coniferyl alcohol in solution. (B) UV spectrum of DHP synthetised in solution. (C) Extinction coefficient (k) of the adsorption layer after twelve hours of the polymerization process. The quantity k is calculated by point per point inversion and is related to the absorption coefficient of the adsorbed molecules...

Yeast alcohol dehydrogenase (ADH) has its highest activity at 30°, and this decreases sharply with increase of temperature above 50°. No activity is observed at 70°. This inactivation process can be monitored by measuring the remaining activity of the enzyme during the incubation at elevated temperatures. ADH from yeast is assayed by monitoring ethanol-dependent NAD reduction at 340 nm ADH activity is expressed as micromoles of NADH produced per minute with a molar absorption coefficient of 6.22 mA/ cm . The influence of molecular chaperonin on ADH inactivation can be examined as follows. 

A copolymer of t-BOC-protected norbornene PNBHFA is shown in Figure 2.19. The t-BOC group is dissociated by a photo-induced proton from PAB to produce alkali-soluble alcohol. The resist gives an L/S of 60 nm and absorption coefficient of 1.9 at 157 nm. i Poly(MA-co-alycyclic norbornene) is... 

Fig. 7.1. Ostwald absorption coefficient (y X 10 ) for argon at 25°C in Hfi, DgO, and some alcohols, as a function of the molecular weight of the solvent. The anomalous low solubility in water is indicated by the vertical line connecting the experimental value with the extrapolated value. [Redrawn from Ben-Naim (1972e).]...

To eliminate the problem of beta changing slowly to alpha, Garrett and Walker, (300) proposed measuring the color at 335 nm, where the alpha and beta forms have the same absorption coefficient. They also studied the kinetics of formation of silicomolybdic acids in very dilute molybdic acid solutions (0.0025 M) and concluded the rate was proportional both to silica concentration and molybdate ion concentration the alpha form had a constant qptical density between pH 2 and 4.5. Alcohol catalyzes the color formation, especially when present at about 30 vol.%, even at pH 5. 

The polypeptin sulfate melts with decomposition at 235. In 70% aqueous isopropyl alcohol solution, it is levorotatory [a] = —93 3 (c = 3%). It has characteristic absorption bands with maxima at 2520, 2580, and 2640 A the absorption coefficient is very high between 2000 and 2400 A, and becomes zero for wavelengths higher than 3000 A. 

Alcohol dehydrogenase is an enzyme that catalyzes the conversion of ethanol to acetaldehyde in yeast (Eq. 10.10). Its activity can be monitored by following the increase in absorbance at 340 nm due to the formation of NADH. NAD+ does not absorb at this wavelength. Given the absorbance data below, calculate the activity of the enzyme in units per mL. One unit of alcohol dehydrogenase is defined as the amount needed to reduce 1 pmole of NAD+ per minute. The molar absorption coefficient, e, is 6220/M/cm. 

Phthalocyanine-based dyes are especially useful for CD-R, as the chromophore absorption band falls in the desirable spectral range, and they are noted for excellent photostability. Unlike cyanine dyes, phthalocyanines tend to have very poor solubility, particularly in solvents such as alcohols and aliphatic hydrocarbons (which do not attack polycarbonate and are therefore used for spin coating). Therefore, the main barrier to the wider use of these dyes is the relatively high cost of synthesizing soluble derivatives. Suitable modifications to the Pc core which have been developed, notably by Mitsui Toatsu, are shown in Scheme 7. The bulky R groups reduce undesirable molecular association (which in turn lower the extinction coefficient and hence reflectivity), whereas partial bromination allows fine-tuning of the film absorbance and reflectivity. The metal atom influences the position of the absorption band, the photostability, and the efficiency of the radiationless transition from the excited state.199 This material is marketed by Ciba as Supergreen.204... 

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