I t would, therefore, seem possible to transfer intensity data bctween instruments if this ratio had been previously determined. A more accurate ratio is obtained if the slope ratio is determined ; however, the same ratio should be obtained if t,he absorbances at one path length were used.
ACKNOWLEDGMENT
LITERATURE CITED
The four instruments uaed here represent one from Canisius College, two from National Aniline Division of Allied Chemical Corp. and one from the Buffalo Semi-Conductor Diviaion of the General Electric Co. We thank these companies for their cooperation.
(1)Behnks, F., Anacreon, R., Pittaburgh Conference on Analytical Chemistry and Applied Speutroscopy, Paper 108, March 1958; raprinta available from
Perkin-Elmer Corp., Norwalk, Corn. (2) Coblentz Society, Appl. Spsdrweow 2, 109 (1957).
The Use of Infrared Band Contours in Applied Spectroscopy Herman
A. Szymanski, Canisius College, Buffalo, N. Y.
contour of infrared bands of T molecules in the vapor state is extensively used in structural analysis BE
of Rmall and symmetrical molecules. A number of workers (9-6, 8) have suggested how these results can be applied to larger unsymmetrical molecules. A study was made of the contours observed for a large number of compounds. of one type to classify the band contours observed so that they may be of use in analysis. The compounds reported are olefins which show a distinct band in the region between 10 and 15 microns. Since the most prevalent spectrophotometers in use have sodium chloride optics, it was felt that band shapes observed with this prism would be of most value. Sodium chloride has its best resolution in this region. Since pressure broadening can change band shapes, spectra measured on gases at about the same vapor premure were compared. Spectra were taken from those reported in the American Petroleum Institute series 44 and by others (S-6, 8). The type of band which lends itself very well to this type of analysis is that which results from an out-of-plane vibration of these molecules. The use of this band for recognizing the type of olefinic structures is discussed in advanced monographs such as the one by Bellamy (1). A planar molecule will generally show a band of this type having a fairly sharp and strong central maxima (&-branch) and well separated P and R branches. The designation of this band as a “type C” is well e8tablished. If addition groups are substituted on a planar molecule which changes its planarity, the band contours will reflect the change. When the substituted masscs are small, the contour resembling the type C will be obtained; however, as the mass is increased the contour will lose its distinct branches until finally only one single maximum is observed. In Table I are listed a number of olefinic compounds where this maea change has occurred; the type of band
observed is classified in one of three Categories.
1. A distinct type C band is okserved. 2. The band contours still show three distinct branches but the Q branch is no longer aa intense. 3. Bands show only one maximum.
The position of these bands is influenced by the number of hydrogens substituted on the ethylenic linkage and compounds in the table are divided into the four possible substitution patterns: R-CH=CH,; RiRAkCH,; RiCH=CH-R2; RIRzC=CH-Rs. The region where each pattern has this band is listed with the compound. Highly
Table 1.
electronegative substituenta show band positions slightly different from t h w observed for saturated hydrocarborn. These divisions are labeled A, B, C, and D. When two double bonds occur in the molecule, several bands due to thie out-of-plane bending can occur. EXamplw of this type are listed aa “special cases." Section A compounda have three hydrogens on the ethylenic linkage, which allows only monosubstitution. This type of substitution shows two distinct bands in the 10- to 11-micron region and both follow the same general shape. If the substitution is chlorine, methyl, or aldehydic, type 1 bands are
Olefins Compounds Bands, Microns
Band Shape
10.05-10.18;10.95-11.05 10.6; 11.25 1.1: 10.96
1
ComDound A.
1 t
2 2 2 3 9.9; 11.0 10.0;10.95 10.1; 11.05;11.3 10.1; 11.1; 12.85 10.0; 10.3; 11.2 10.1;10.9 10.0: 10.9 11.1b-11.30 12.45 11.1
B.
11.3
11.3 11.3 11.3;11.65 10.3-10.4(trans); 14.6 (cia) 10.4 14.8 10.4 14.4 10.4 10.4 13.3
C.
D.
CF;CFH-
14.6 10.4; 11.2 11.8-12.7 12.5 13.4 13.5 VOL. 33, NO. 6, M A Y 1961
1 2 2 2 2 3 3 1 1 1 2 3 1
2 2 2 2-3 3 3 3 2 2 2 1 1
81s
obtained. When an ethyl group is substituted, a type 2 band results, while propyl and all larger gronps give type 3. Compounds such as vinyl ethyl ether or vinyl methyl ketone show type 2 bands displaced from the positions of the alkylabstituted ampounds. Compounds where two hydrogens remain on one of the carbons of the ethylenic linkage are listed in section B. Two substituents are, therefore, possible. ‘Two fluoro or methyl groups when substituted give type 1 bands. Type 1 is also obtained for the compound CHpCCHaCCH containing an acetylenic substituted group, but a methyl with the second substituent, an ethyl, gives type 2 aud E butyl with a methyl gives type 3. All larger substituents give type 3. Where one hydrogen occurs on each carbon of the double bond, cis and trans
isomers are possible, each form showing bands in Merent positions. Both forms show similar band contoura for the w e substituents. When two methyl gmups rn suhtituted, type 2 bands are found. Ethyl-methyl substituents show type 2, the cis form being almost type 3. Groups larger than this all give type 3. The compound CF,CHCHF, shows type 3 bands. Cyclopentene shows type 2 bands, not unexpectedly, since the substituents could be considered to be near that of the ethyl-methyl one. Qclopentadiene baa type 2. When only one hydrogen remains on the ethylinic linkage, three substituents are possible. Three methyl groups Substituted give a type 2 band; 1,ldifluoro-Z-chlorcethene however, and l,l,%triftuoroethene have type 1 bands. Any substituents larger than methyl give type C bands.
Where two double bonds occur in the molecule, the compounds may fall into one classification of A, B, C, D, or into two. In both cases, the mass of the group substituted m n n d the double bond will determine if type 1, 2, or 3 band contours will be observed. REFERENCES
Bellamy, L., “Intrared spectra of Corn lex Molecnlen;’ 2nd ed.,Methuen and %., London, 1958. (2) Fdgell, W. Potter, R., J . C h .PAwa. (1)
24, 80 (19561. (3) Mann, D., Acquista, N., Plyler, E., IM., 21, 1949 (1953). (4) Ibid., 22, 1586 (1954). (5) Nielson, J., Lian C., Smith, D., IM., 20, 1090 (19527. (0) Piernon, R., Fletcher A,, Gants, E., ANAL.bar. 28, 1218 (1950). (7) Potta W., Nyquist, R. A,, Spcdrcchim. Ada 1959! 079. (8) Smith, D., Nieleon, J., C h s e n , II., J. C h m . PAYS.18, 326 (1950).
A Simple Glass Variable-Thickness Cell for Visible, Ultraviolet, and Near-Infrared Spectrophotometry Ernest J. Breda’ and Esko V. Kotkas, E. I. du Pont de Nemoun B Ca., Inc., Eastern Laboratc N making differential spectrophotoImetric measurements, exact background compensation . is essential. Background compensation can be achieved by adjusting either the concentratiou or the thickness of the reference solution. Adjustment of solution thickness is more convenient but requires a suitable cell of variable length to hold the solution. Commercially available variablepath cells are expensive and are usually limited to path lengths varying from 0 to 10 mm. An inexpensive, yet versatile, glass cell for solution thicknesses up to 5 cm. or more, for use in ultraviolet, visible, and near-infrared spectrophotometry, was constructed from a hypodermic syringe and silica windows. A B-D Cornwall, Luer-Lok (Becton, Dickiuson, and Co., Rutherford, N. J., No. 1270s) glass syringe of IO-ml. capacity with 0.5-ml. graduations ( 1 6 mm. inside crosssectional diameter of plunger) was used. The two ends each of the outer body and of the hollow plunger were cut off with a rubberbonded, 120-mesh aluminum oxide grit wheel by wet cut to form concentric tubes each of uniform diameter. A 2to 3-mm. diameter hole was drilled near the forward (0-ml. graduation mark) end of the outer tube. The neck of a 50-ml. volumetric flask with a ground stopper was cut off to a length of 4.0 to 4.5 em. The cut end of the neck was ground to fit the curved surface of the outer syringe tube at the location of the hole. The neck was sealed to the tube at this point to serve as a reservoir. 1 Present address, E. I. du Pont de Nemoum and Co., Inc., Beaumont Works, Beaumont, Tex.
816
ANALYTICAL CHEMISTRY
Cements such as Sealstix, Dekadheae, or litharge and glycerol were Used. Matched quartz ultrasil windows (PYrw Mfg. cO., New N. Y.,.No. eter S n for Mthe ) ,%eouter inchtube thick, and !&mm. 19-mm, dmmdimeter for the inner tube, were sddto the forward ground ends of the tubes by one of the above-mentioned ments. The assembled cell is shown in Figure 1. The described cell functioned satisfactorily with a number of common solvents, such as aqueous acidic, alkaline, and various d t solutions, and with alcoholic, ethereal, and hydrocarbon systems. However, aqueous ammoniacal solutions softened the Sealstix cement and ethylene dichloride
Figure 1. Exploded view of cell assembly
I
compewy UUIWIYC:~ wit: uekadbese cement. The dieadvantage of wing litharge and glycerol as cement is its slow setting property. No other cementwas tried. The quartz m t r d windows are clsimed to transmit 85 $0 93% Of the incident e n e W in the entire spectral range from 2ooo to 25,000 A. Solution thickneaspa over 5 em. are obtained by reversing the plunger part of the assembly. Using the graduations on the syringe, the reproducibility of cell thicknesses WBS within *5% at the 1-m. level and +1% at the 5cm. level. No leakage past the plunger nor change in solution thickness was noticeable after the resewoir was stoppered. No lubrication of the plunger was necessary.
