Infrared Spectra of Bromochloromethane, Dibromo Methane, Tribromochloromethane, and Tetrabromo Methane by Earle K
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U. S. Department of Commerce Research Paper RP2097 National Bureau of Standards Volume 44, May 1950 Part of the Journal of Research of the National Bureau of Standards Infrared Spectra of Bromochloromethane, Dibromo methane, Tribromochloromethane, and Tetrabromo methane By Earle K. Plyler, W. Harold Smith, and N. Acquista The infrared spectra of bromochloI'omethane, dibromomethane, tribromochloI'omethane, and tetrabromomethane have been mea ured from 2 to 36 microns. By the use of the results of other workers in Raman spectra it has been possible to classify all the strong bands that have been observed. Many of the weaker bands were classifi ed as combination a nd over tone. Only a few of the bands of tetrabromomethane were observed, on account of the breaking down of the compound in solutions of carbon disulfide and carbon tetrachloride. The in tense bands of dibromometha ne and tetrabromomethane were measured in the vapor state. The infrared absorption bands of these compounds had not previou ly b een measured over an extend ed range of wavelength , and these measurements were undertaken to deter mine t he po itions of weak bands 0 that a more complete classifi cation of the spectra of t hese molecule co uld be made. 1. Introduction band 0 that the combination bands co uld be cla sified. Other workers have measured the vibrational bands of a number of substituted methanes in the II. Experimental Observations infrared region, and also the frequencie have been determined by Raman spectra. From theory it A P erkin-Elmer spectrometer was used for all ha been determined that molecules of the type of measurements with lithium fluoride, potassium CX4 show two active and two inactive funda bromide, sodium chloride, and thallium bromide mentals. Wllere interaction occurs the inactive iodide prisms to cover the wavelength range of 2 to frequencie al 0 appear in the infrared spectrum. 36 f.L . In the spectral region of 2 to 24 f.L , cell m en the sub tituted atoms are of more than one thicknesses of 0.2, 0.1 , and 0.05 mm were u ed to species, the degeneracy is removed and nine bring out most of the bands. For very strong fundamentals are present in the spectrum. In a bands the compounds were diluted either in carbon molecule of the type CXY3, the degeneracy is only tetrachloride or in carbon disulfide, or liq uid films partly removed and six fundamentals are found in with a thickness of 0.01 mm or less were formed the spectrum. between two potassium bromide windows. In the The four substituted methanes, bromochloro thallium bromide-iodide region between 24 and methane, dibromomethane, tribromochloro 36 f.L it was necessary to use cell thicknesses of 1.5 methane, and carbon tetrabromide, represent the mm to bring out the weaker absorption bands. the three types of molecules that give nine, SL"X, and The method of measurement and the reducing of two active fundamentals in the infrared spectrum. data have been de cribed in a previous paper [1 ].I The infrared bands of these compounds had not Bromochloromethane, dibromomethane, and tri previously been measured over an extended range bromo chloromethane were obtained from the Dow of wavelengths, and these measurements were 1 Figures in brackets indicate the literature references at the end of this undertaken to determine the positions of the weak paper. Infrared Spectra of Halogenated Methanes 503 !"'I I Chemical Company and tetrabromomethane from not measured, but it is estimated that they were the Eastman Kodak Company. of the order of 0.005 mm. This estimate of the Purification consisted of treatments until an thickness was made on the basis of the percentage examination of the products indicated satisfactory absorption that was observed in a O.l-mm cell agreement with accepted physical constants. To when the compound had been diluted with a trans avoid any effect of oxygen, the infrared measure parent solvent. The reason that the thin cell was ments were made as quickly as possible after employed was to locate the position of the band purifica tion. accurately for the pure liquid in regions of intense Figure 1 shows the absorption spectra of the absorption. In figure 1 the portions of the ab four halogenated methane derivatives in the region sorption curves represented by broken lines indi from 2 to 15 JL . The cell thicknesses and other cate that small details could not be accurately conditions of the measurements are given on the determined on account of the absorption of the figure and in the captions. The intense bands solvents or the absorption of atmospheric bands. were observed by use of a cell that contained a As tribromochloromethane and tetrabromometh thin layer of the material. The cell was made by ane are solids at room temperature, their spectra placing a small quantity of the liquid on a plate were determined in solutions of carbon tetrachlo of potassium bromide and then pressing another ride and carbon disulfide. There was a tendency plate on the top without the use of a shim. The for the solutions of tetrabromomethane to darken thiclmesses of the cells made in this manner were on standing, and the absorption spectrum was WAVE NUMBERS IN CM-' ' DOC ' DOC 1500 1300 1000 800 100 .\r: ......-....... ,··.... ·, \. v 80 60 40 '0 8- 15,11 in CSz 4 0 ce', cl 20 8 0 2-7}J in CC! .. O.2mm 60 40 20 WAVELENGTH IN MICRO NS FIGURE 1. Infrared absorption spectm of bromo chloromethane, dibromomethan e, tribromochloromethane,. and tetrabromomethane. Tribrornochlorornetbane and tetrabromornethane were dissolved in carbon tetrachloride and carbon disulfide. The solution concentration of tribromo chloromethane in carbon tetrachloride is 3.1 giml, and in carbon disulfide, 2.4 gim! for the observations in 0.2-mm celL For tbe insert bands the concentration is 0.14 gimL Saturated solutions of tetrabrornometban e were prepared in each solvent, 504 Journal of Research measured immediately after their preparation. a saturated solu tion in methylcyclohexftne wa The observations were repeated several times and used. The methylcyelohexane has a high trans the same bands were always found. Since it was mittance in this region, and its spectrum shows possible to account for all the observed bands as only one absorption band when a cell 1.5 mm combinations, overtones, or fundamentals, it docs thick i used. not seem probable that any of the observed bands In figures 3 and 4 are shown some of the absorp were produced by products of decomposition or tion bands of dibromomethane and tetrabromo oxidation in the solution. methane measured in the vapor state. The Figure 2 shows the long wavelengt.h spectra of substances were placed in the bottom of a cell 40 the four substituted me thanes from 14 to 36 )1.. em long, which was not evacuated, and allowed Some general absorption was observed in the to remain in the cell for several hours. On re pectra of bromo chloromethane and dibromometh peating the measurements 6 hours later, it was ane from 28 to 36 )1., but no definite bands could found that the bands did not increase in intensity. be found in this region. For the measurement of It is probable that the vapors were at a saturated tribromochloromethane in the region of 24 to 36 )1. , condition in the air of the cell at 25° C. WAVE NUMBERS IN GM-I 700 600 500 4 50 400 350 300 80 60 4 0 --v------- '-"-----~ ~:"-~ ---------- -- ---- -------------- 20 O.2 mm 1.5mm O.lmm BO 60 40 20 CSr... 0 14 16 18 20 22 24 26 28 30 32 34 36 WAVELENGTH IN MI CRONS FIGURE 2, Absorption spectra of bromochlo. omethane, dibro1l!0methane, t1'ibromochloromethane, and tetra bromo methane in the re gion from 14 to 36 JL. A sollltion conccntration o[ 4.0 g/ml in carbon disulfide was llscd [or tribrornocblorometbanc wi th the O.l-mm cell . A concentration of 0.14 gl ml was used in the O.05-mm cell . A saturated solution in methylcyclobcxane was used in the reg ion o[ 24 to 36,... Infrared Spectra of Halogenated Methanes 50S WAVE NUMBERS IN Ct,,-' of W . Bacher and J. Wagner [2]. The other fun 1250 1000 8 00 661 511 100 damental bands, as determined by Raman spectra, ~ ~ check within a few wavenumbers with infrared <.) 80 I!''" measurem ents given in table 1, except P7 , which 60 z l 0 was estimated by them at 724 cm- from Raman in '" 4 0 ~z ., 20 CH2 Br;! VAPOR TABLE 1. Observed frequencies of the infrared bands of 40cm ~'" bromochloromethane, dibromomethane, tribromochlorome 0 7 10 12 13 14 15 16 11 Ie thane, tetrabromomethane, and their assigllments WA" VELENGTH IN MI CRONS FIGUR E 3. Absorption spectrum of dibromomethane vapor Classification A ' Classification ~I I from 7 to 18 Jl. _________ ________L- The more intense absorption is for tbe saturated vapor (45 mm of H g at RROMOC[ILOROMETHANE DIRROMETHANE VAPOR 25° C). WAVE NUMBERS IN CM-' Mi· Mi- 800 667 cm - 1 crons em-I crons 1'4 ___ ___________ 100 r----L~~--------_r--------~------~ a 226( R) 44.2 --------.----. 1, 233 8. 11 "2 ______________ 606 16.51 v8 ___ ___________ 1, 195 8.37 VIJ ______________ 728 13.73 1'7 ______________ 810 12.34 Vi _________ _____ 852 11. 76 ? - --------._--- i45 13. 42 V.5 _________ _____ 1, 130 8.85 Vll ____ __________ 648 80 v8 _______ _______ 1, 225 8. 16 V2 ______________ 591 P3---_________ __ 1, 402 7. 13 ..... V1 _____ _ _ _ _ ____ _ 2, 987 3.348 z ..