Infrared Spectra of Bromochloromethane, Dibromo Methane, Tribromochloromethane, and Tetrabromo Methane by Earle K

Home , Bromochloromethane, Carbon tetrabromide, Dibromomethane

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

8- 15,11 in CSz 4 0 ce', cl 20

8 0 2-7}J in CC! .. O.2mm

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

60 4 0 --v------'-"-----~ ~:"-~ ------20

O.2 mm 1.5mm

O.lmm

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 ... V6 ______3, 060 3. 268 T RIRROMOCFfLOROMli: THANE (.) VZ -P4 ______377 26.5 a: 60 ... v7-V4. ______15. 65 Go. 638 pZ5 ______Jl4+v9 ______a 141 (R ) 70.9 Z 950 10.52 V79 ______a 214 (R ) Q 1. 261 7.93 46. 7 Ul ? ------114 ______112+ 117 ______215(calc.) 46.5 1,331 7. 51 V3 ______'":iii 2V9 ______1, 453 6.88 329 30. 4 Ul 40 P6S ______575 14. 81 z C8r 4 VAPOR Jl5+"8 ______1, 969 5. 08 « Vl ______74 7 13.39 It: JlZ+Vl ______2, 004 4. 99 Jl 2S+Vi9 ______I- 40 em 117+"8 ______2,006 4. 84 355 28. 2 2V4,211 79 ______436 22. 9 Jl3+ V9 ______2, 119 4. 72 Jl3+V25 ______20 Jll+v7 ______2, 242 4. 460 467 21. 4 Vl-PL ______2v8 ______2, 450 4. 082 525 19.01 Jl3+Vill ______Jl3+Jl 8 ______2,639 3. 789 545 18.35 PI-P2,s- - ______2v3 ______2,803 3. 568 608 16. 44 PI+P1I ______735 13. 61 O~ ______~ ______~ ______~ ______~ 3,751 2.655 ? ------2V4+V3- ______-- .116+ P1 ______3,939 2. 539 769 13. 00 V68+V2,s ______12 13 14 15 16 Vl + v 8 ______4, 228 2. 365 8J 7 12. 24 Vi9+VI8 ______WAVELENGTH IN MICRONS JI3+Vtl ______4, 502 2. 221 872 11. 47 V68+V4 ______886 11. 28 FIGUR E 4. Absorption bands at 12.6 and 14.9 Jl. f or satu· ? ------933 10. 69 V68+Vl ______rated vapor of tetrabromomethane at room temperature. DIRROMOMETHANE 1, 006 9.94 Vl+Vl ______1, 068 9.33 Vt+V2,s+V79 _____ 1, 114 8.98 v4 ______• 174(R) 57.5 III. Discussion Jll +P2,s+P68 _____ 1, 141 8.76 .112 ______579 17. 27 ZV 68 ______1,350 7.40 ViI ______639 15.66 In table 1 are given the wavelengths and fre 11 7 ______813 12.29 quencies of th e observed bands. These bands 115 ______1, 096 9. 12 TETRABROlfOll ETHAKE .IIS ______1, 190 8. 40 vl ______1,385 7.22 have been interpreted as fundamentals, combina V2 5 ______111 ______2,988 3.347 a 123(R) 81. 3 tions, and harmonics. The numbering of the PHD ______.116 ______3, 065 3. 263 a 183(R) 54.6 Vl ______a 257(R) levels is in accordance with that adopted for corre v 9- 1I4 ______466 21. 5 37.4 • VI68 ______669 14. 95 lation of a large number of molecules of different ? ------729 13.71 V5-v4 ______922 10.85 P1 6S+v3+V4i9 ____ 74 8 13.36 P25+PI6S ______12. 70 symmetries , as will be discussed in a forthcoming V4+ v 8 ______J,366 7.32 787 V3+ VI6S ______V5+V7 ______1,912 5. 23 934 10.71 paper by Plyler and Benedict. Eight of the 2111 68 ______v l+v2 ______1, 961 5. 10 133 7. 50 infrared active fundamentals of bromochloro .IIl+vtI ______2, 020 4. 95 2P5 ______methane have been observed, and the other, 2, 179 4.59 TETRARROlfOMET H AKE VA POR Pl+v8 ______2, 587 3. 866 occurring at 226 em- I, was outside the range of vtl+P7 ______3,909 2. 558 the thallium bromide-iodide prism. In th e deter Vl+V8 ______4, 195 2.384 .,'+"16' ______1 796 12.57 V3+V6 ______4, 488 2. 228 V1 68 ______678 14. 74 mination of th e combination bands for this com I

pound th e Raman value was used from the work a (R) indicat.es Raman value obtained from li terature.

506 Journal of Research

L J pectra, and has been observed by us in the was covered in these measurements. The other infrared spectra as a strong band at 852 cm- I . three fundamentals fall beyond the range of the All of the fundamental bands of dibromome thallium bromide-iodide pnsm. Calculation thane have been observed in the infrared spectrum show that two of these bands, )/79 and 1'4, should except )/ 4 at 174 cm- I • This value has been have frequ encies at 214 and 215 cm- I , respec determined by Dadieu and Kohlrausch and several tively. The calculated values are in good agree other workers in Raman spectra [3]. The Raman ment with the wavenumber of a single Raman spectra for the remaining eight fundamentals check line determined by Lecomte and coworkers [4] . well with these observations, except that )/7 and For the classification of the combination and )/s are found at 813 and 1,190 cm- I , respectively, harmonic bands, the Raman values 141 and 214 in the infrared as compared to 723 and 1,13 3 cm- I have been used. The three fundamentals cm- I , respectively, in the Raman spectrum as observed in the infrared checked within 5 cm- 1 reported by Dadieu and Kohlrausch . The other with the Raman values of Lecomte. The differ observed bands, except for a few weak ones, have ences between the infrared and Raman values been classified on the basis of the nine funda may be attributed to the effect of the solvent mentals. carbon disulfide on the tribromochloromethane in A close similarity between the spectrum of producing a small shift in the bands, and also to dibromomethane and of bromo chloromethane is the presence at 667 cm- I of the absorption band observed. The eff ect of replacing the chlorine in of atmospheric CO2, which mad e it difficult to bromochloromethane by the heavier atom bromine locate accurately the position of the band at is to shift corresponding vibrations to longer wave 675 cm- I . The two absorption bands at 735 and lengths. The shift is observed for all frequ encies 933 cm- I could not be accounted for on the basi except those involving primarily C- H stretching of the fundamentals. vibrations. As can be seen from table 1, the In comparing the fundamentals of tribromo values of )/1 and of )/6 for the two compounds fall chloromethane and tetrabromomethane, it is within 5 cm- I of each other. This difference in seen that the substitution of the bromine atom wavenumber is almost within the limit of experi for the chlorine atom reduces the number of mental error for this region of the spectrum. fundamentals from six to four. Only the two The spectrum of dibromomethane was also threefold degenerate vibrations, )/1 68 and )/ 479 , are determined in the vapor state for some of the infrared active. The remaining two appear in intense bands, so that a comparison could be made combination. On e of these bands, )/1 68, with with the liquid state. . The type of bands at frequency 669 cm- I , was observed in the rocksalt 1,195 and 648 cm- I co uld not be determined with region. This is 4 cm -I greater than the Raman the prism instrument available. For the band at value as determined by D adieu and Kohlrau cll 1,190 cm- I in the liquid state there is a small [5]. This difference can probably be attributed shift to 1,195 cm- I in the vapor state. The other to error of observation caused by the pre ence at band shifted from 639 to 648 cm - 1. Two of the 667 cm- I of the absorption band of atmospheric remaining bands located at 810 and 591 cm- I CO2. The other bands in the ob erved spectrum, show defini te zero branches when measured in the which are of low intensity, can be interpreted on vapor state. These bands have shifted from 813 the basis of the four fundamentals. Three of the and 579 cm- I , respectively, as measured in the fundamentals listed in table 1 are the Raman liquid state. The vapor band at 745 cm- I is values determined by Dadieu and Kohlrausch. shifted 16 cm- I from the liquid band at 729 cm- 1 The classification of the bands as given in table 1 and may have a zero branch. The comparison of accounts for most of the observed bands. The the positions of the bands in the liquid and in the band observed at 729 cm- I in dibromomethane vapor states shows that there is a small change was not classified and may have arisen from a small in the frequencies when measured in the two amount of bromo chloromethane that was present different states. as an impurity. There was observed an intense Of the six active infrared fundamentals of band in this region for bromo chloromethane. tribromochloromethane, only three bands, )/1 , 1'68, When the vapor of dibromomethane was meas and )/3, were observed in the infrared region that ured, the ratio of intensities of the bands at 735

Infrared Spectra of Halogenated Methanes 507 cm- I and 813 cm- I were much different than in and bromo chloromethane into a series of lines the liquid, and also a band at 1,233 cm- I appeared. approximately 1.5 cm- I apart. The spacing This is near the location of another intense band interval is less for dibromomethane than for of bromo chloromethane at 1,225 cm'-I as measured bromo chloromethane. in the liquid state. Another sample of dibromo methane was measured that also contained these bands. According to mass spectrograph deter The authors thank W. S. Benedict of thi minations it contained about 1 percent of chlorine. Bureau for his discussions on the classification of It is probable that a small amount of bromo the bands of these compounds. chloromethane is present in the dibromomethan e and produces the bands that do not fall in the IV. References classification scheme. On further purification of [1] E. K. Plyler, R. Stair, and C. J. Humphreys, J. dibromomethane it was found that the band R esearch N BS 38, 211 (1947). in the region of 13.6 jJ. (729 cm- I ) disappeared [2] W. Bacher a nd J . Wagner, Z. physik Chern . (B) <13 , when the compound was measurcd in cells 0.1 191 (1939). [3] A. D adieu and K . W . F . K ohlrausch, Mh. Chern. 55, mm thiclc 58 (1930); 57, 488 (1931). Without a study of the rotational structure of [4] J . Lecomte, H . Volkringer, and A. T chakirian, J. these bands the molecular constants cannot be phys. radium 9, 105 (1938). obtained. Unpublished observations made with [5] A. Dadieu and K. V,T. F . Kohlra usch, Mh. Chern. 57, a different instrument show resolut ion of some 488 (1930). of the near infrared bands of dibromomethane WASHINGTO N, November 18, 1949.

508 Journal of Research