Mulls Nujol

The Nujol (mineral oil) mull is also often used for solids. In this method, a small amount of the finely divided solid analyte (one or two micron particles) is mixed together with an amount of mineral oil to form a mixture with a toothpaste-like consistency. This mixture is then placed (lightly squeezed) between 

An important raw material for pharmaceutical formulations is polyethylene oxide because it is used in many and various products. Polyethylene oxide is a solid material purchased in bulk as a powder. Sampling technicians collect samples in glass bottles. In the laboratory, small portions are taken and mixed with potassium bromide for the purpose of producing a KBr pellet and obtaining the IR spectrum. The spectrum thus obtained is compared to a reference spectrum to confirm that the material is indeed polyethylene oxide. 

Jessica Weinland fills a KBr pellet die with a KBr-polyethylene oxide sample. Right, Ms. Weinland uses a laboratory press to create the pellet. Notice the pellet die positioned in the press in the photo on the right 

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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).

Cyclodimer 3 proved to be somewhat difficult to manipulate, thus contributing to the complexity of its characterization. The bowed diacetylenic linkages revealed in the X-ray data impart surprising physical characteristics to the molecule. The energy-rich hydrocarbon was sufficiently strained that it decomposed explosively upon grinding (i. e. preparing a Nujol mull) or when heated above 80°C. At room temperature, crystals blackened within a few days and apparently auto-polymerized, even when stored under vacuum in the dark. Only dilute solutions of 3 in benzene or pyridine were fairly stable over time, especially when stored cold under an inert atmosphere. 

Since solid-state reactions can easily be monitored by continuous measurement of spectra, it is easy to study the mechanism of the reactions. For this purpose, IR spectroscopy is the most useful, because IR spectra can be measured simply as Nujol mulls or directly for any mixture of solid-solid, solid-liquid, or liquid-liquid by using the ATP (attenuated total reflection) method. Some such examples of the mechanistic study are described. 

Until recently the products of all nitrile cyclizations by the Thorpe reaction had been formulated as imines, although the products were found in 1955 to be better written as the enamine structure. In order to verify the reaction mechanism of the Thorpe reaction, the solid-state reaction of 84 and Bu OK was monitored by measurement of IR spectra in Nujol mulls. As the reaction proceeds (Scheme 14), the CN absorption of 84 at 2250 cm" decreases and a new CN absorption of the imine intermediate (87) arises at 2143 cm As 87 is converted into 88 by a proton migration, the CN absorption of 87 at 2143 cm" disappears, and only the CN absorption of 88 at 2189 cm remains finally [13]. 

In order to clarify the reason why the Rap-Stoermer reaction proceeds so efficiently under solvent-free conditions, the K2C03-assisted reaction of 89a and 90a was studied by IR spectral monitoring in Nujol mulls [ 16]. Firstly, the potassium salt formation of 89a was studied (Scheme 16). One minute after mixing of 89a with twice the molar amount of K2CO3, a vC=0 absorption band (B) appeared at 1692 cm" (spectrum II in Fig. 1), although 89a itself shows vC=0 absorption (A) at 1664 cm (spectrum I in Fig. 1). After 10 min, B disappeared and a new vC=0 absorption band (C) appeared at 1670 cm (spectrum III in... 

Fig.l IR spectra of a mixture of 89a and twice the molar amount of K2CO3 in Nujol mulls. I Pure 89a for reference II1 min after mixing III 10 min after mixing... 

Fig. 2 IR monitoring of the K2C03-assisted solvent-free reaction of 89a with 90a by spectroscopic measurements in Nujol mulls. I-IV measured every 15 min...

Fig. 3 Monitoring for 40 min of the solvent-free benzoylation of 20 with 101b at 80 °C by IR spectral measurements in Nujol mulls...

Italic values of SO stretching frequencies are solution values. All others are for Nujol mulls. 

Molar ratio of host and guest is 1 2 in all complexes. b All IR spectra were measured in Nujol mull. 

Methods. FTIR spectra were obtained in nujol mull on a Perkin Elmer model No. 1700GC-IR spectrophotometer. 1H NMR spectra were obtained at 363 MHz. 13C NMR spectra were obtained at 91 MHz. 

The sparingly water-soluble triethylammonium saltofBi2H122-is readily converted to the highly water-soluble sodium salt. A carefully weighed sample of the triethylammonium salt is treated with an exactly equivalent amount of standardized aqueous sodium hydroxide. The mixture is heated to effect solution and then boiled to expel the free triethylamine until the vapors are no longer basic. Evaporation to dryness then leaves a crystalline hydrate of Na2Bi2Hi2. The anhydrous salt is obtained by drying at 100°/1 n for 24 hours and has characteristic infrared absorption frequencies as a Nujol mull (exclusive of any frequencies coincident with Nujol) at 2470 (s), 1010 (w), 1070 (m), 770 (w), 727 (m),710 (m),and 700 (m) cm. 1... 

Methylcarborane is an air-stable, white crystalline solid which is soluble in common organic solvents. The infrared spectrum (Nujol mull) contains major absorption bands at 3.90 (s), 8.83 (w), 9.12 (w), 9.69 (w), 9.83 (w), 10.03 (w), and 13.85 (s) p. The proton nuclear magnetic resonance spectrum of a carbon tetrachloride solution of methylcarborane contains a broad —CH resonance of intensity 1 at 6.52 r and a —CH3 resonance of intensity 3 at 8.02 r. 

Triphenylphosphine selenide crystallizes from absolute ethanol as small white needles which melt at 187 to 188°. The compound is very soluble in dichloromethane moderately soluble in hot methanol, hot ethanol, hot acetonitrile, hot benzene, and hot 1-butanol and insoluble in ether and water. The PSe infrared stretching frequency occurs at 562 cm.-1 (Nujol mull). 

The situation with 7V-acyloxy-/V-alkoxyureas and carbamates is similar although infrared data were mostly determined by liquid film or condensed phase (KBr/nujol mull).52,131 However, the limited data for V-acyloxy-TV-alkoxyureas (Table 2, entries 69-72) give amide carbonyl frequencies ca. 1730 cm-1 that are raised by some 37-40 cm-1 by acyloxylation. Values for carbamates (Table 2, entries 73-77) are higher (mostly 1780 cm-1) but are raised to a lesser extent (10-20 cm-1) relative to their parent carbamates. Clearly, carbonyl vibrational frequencies will be influenced strongly by the adjacent amino or alkoxyl group in both analogues. 

Figures 6 and 7. Spectra were run on a Perkin-Elmer Model 467 grating spectrophotometer as a KC1 pellet (1 mg/200 mg KCl), and as a Nujol mull (20 mg/3 drops). The spectra are essentially identical. The CTC-HC1 spectrum may also be found in a compilation of IR spectra of Drug Reference Standards by Hayden et al. (26). Major absorption frequencies have been compiled (27) and assignments have been made on many of the bands(28-31). Some of the major frequencies and band assignments are ...

Figure 7. Infrared absorption spectrum of CTC-HC1 as Nujol mull. 

Figure 9.21 Infrared spectrum of aspirin, i.e. 2-acetoxybenzoic acid. (Solid aspirin was prepared within a Nujol mull)...

A rapid, inexpensive way to get an IR of solids is to mix them with Nujol, a commercially available mineral oil. Traditionally this is called making a Nujol mull, and it is practically idiomatic among chemists. Though you won t see Rexall or Johnson Johnson mulls, the generic brand mineral oil mull is often used. 

Phase. For KBr, say solid KBr. A Nujol mull is Nujol mull. Liquids are either solutions in solvents or neat liquids, that is, without any solvents, so call them liquids. 

Dissolve in a solvent and then use a liquid sampling cell to measure the solution 2) dissolve in a solvent, place several drops of the solution on a salt plate, evaporate the solvent, and measure the residue 3) KBr pellet 4) Nujol mull and 5) reflectance. 

A Nujol mull is a mixture of a solid sample with Nujol, or mineral oil, for the purpose of more conveniently obtaining an infrared spectrum of the solid sample. 

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