Mulls

Non-volatile, viscous liquids can be analysed as films supported on, or between, infrared windows. Samples that are difficult to spread can be taken up in a volatile solvent (such as methanol or ether), and cast onto the window by applying a drop of solution to the window. A heat lamp will quickly drive off the solvent leaving a thin film. 

Thicker liquids will behave like mulls and can be trapped between two windows. To obtain good-quality spectra, the separation of the plates should be around 25 microns, although non-polar materials may need much greater pathlengths for adequate spectra. 

Remember that absorbance values must be used for all quantitative 

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Cl2C = CCl CCl =CCl2. Colourless viscous liquid b.p. 210-211 C. Principally used as a dispersant material for obtaining i.r. spectra of solids in mulls. Skin irritant. 

Nujol A trade name for a heavy medicinal liquid paraffin. Extensively used as a mulling agent in spectroscopy. 

Transparent solid samples can be analyzed directly by placing them in the IR beam. Most solid samples, however, are opaque and must be dispersed in a more transparent medium before recording a traditional transmission spectrum. If a suitable solvent is available, then the solid can be analyzed by preparing a solution and analyzing as described earlier. When a suitable solvent is not available, solid samples may be analyzed by preparing a mull of the finely powdered sample with a suitable oil. Alternatively, the powdered sample can be mixed with KBr and pressed into an optically transparent pellet. 

Both cold- and warm-coating processes employ solutions of phenoHc resins. The principal process used for foundry resins is the hot-coating process. It is the fastest, least expensive, and safest process, and it requires no volatile removal. The sand is heated to 135—170°C in a muller, and soHd novolak resin in flake form is added, which melts quickly and coats the sand. A lubricant may be added at this point. After one minute of mulling, the batch is cooled by adding water, which evaporates rapidly. 

IR and Raman studies of heterocycles today cover two different fields. For simple and symmetrical molecules very elaborate experiments (argon matrices, isotopic labelling) and complex calculations lead to the complete assignment of the fundamentals, tones and harmonics. However, the description of modes ought to be only approximate, since in a molecule like pyrazole there are no pure ones. This means that it is not correct to write that the band at 878 cm is y(CH), and the only correct assertion is that the y(CH) mode contributes to the band. On the other hand, IR spectroscopy is used as an analytical tool for identifying structures, and in this case, bands are assigned to r-iCO) or 5(NH) on the basis of a simple Nujol mull spectrum and conventional tables. Both atttitudes, almost antagonistic to each other, are discussed in this section. 

Mason has determined the infrared spectrum of pyrido[3,2-d]-pyrimidin-4(3ff)-one (149, N in position 5) in chloroform solution and as a KBr disc and has suggested that the low frequency of th e NH band (3389 cm ) and high frequency of the C=0 band (1745 cm i) in the solution spectra are indicative of a quasi o-quinonoid form. The infrared spectra of the four pyridopyrimidin-4(377)-ones (149), the four 2,4(ljff,3//)-diones (150), and a number of substituted derivatives, have been determined, as Nujol mulls, in these laboratories. ... 

Another rather extensive series of similar data, obtained using CS2 solutions and nujol mulls, has been published by Shindo (Fig. 4). His series include considerable data for jS-substituted compounds, for which the question of a choice of substituent constants does not arise. His data also show considerable scatter but seem to suggest strongly that <7+-values are indicated for + M substituents and normal <7-values for —M substituents. The conclusion is confirmed by the short series of similar data reported by Costa and Blasina and by Shupack and Orchin. The data of the latter authors for the NO frequencies in mws-ethylene pyridine N-oxide dichloroplatinum(II) complexes are also moderately well correlated with <7+-values. 

Fig. 4. The N—O stretching frequencies of substituted pyridine 1-oxides (a) in CS2 and (b) in Nujol mull cf. ref. 47. Solid circles if a = a = a crossed circles, a = a+ barred circle, a ( a) open circle, a = a cross, a+ ( ar).

Dunst messer, m. atmometer. -mittel, n. (Leather) mulling agent, -rohr, n. ventilating pipe. 

Gluh-verlust, m. loss on ignition, -waohs, n. gilder s wax. -wem, m. mulled wine, -zone, /. zone of incandescence, -ziinder, m. electric igniter. 

Haus-mlttel, n. household remedy. -mUll, n. hoiisehold refuse, -schwamm, m. dry rot. -seife, /. household soap, specif, common curd soap home-made soap. 

Mull, m. n. mull, (light) muslin lint Mull. Miill, n. tk m. dust, dry mold refuse. Mullbinde, /. lint bandage. 

Torf-kohle, /. peat charcoal, -koks, m. peat coke, -lager, n. peat bed peat yard, -masse, /. peat, -mehl, n. powdered peat, -moos, n. peat moss, specif, sphagnum moss, -mull, n. peat dust, peat litter, -rauchge-schmack, m. fiavor of peat smoke, -staub, m. peat dust, -teer, m. peat tar. -verkoh-lung, /. peat charring, -watte, /. peat wadding. 

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