ANALYTICAL CHEMISTRY
1470 a Ca isoparaffin having one alkyl substituent per molecule. This result is consistent with the physical properties of the wax, which is a soft petrolatum. The four engine oil samples consisted of the saturated fractions obtained by percolation of the oils through silica gel. Since the standard deviations obtained by repeated analysis of a single sample are of the order of 0.01 in weight fraction methyl groups and 0.02 in weight fraction methylene groups, these results show that there are composition differences among the four oils which can be detected by this method of analysis. The medicinal oil is very different structurally from the engine oils. It is indicated to contain a larger concentration of methyl and cyclohexyl methylenes and a smaller concentration of paraffinic methylene groups than the engine oils. It is probable that the approximately 25% of the oil samples which is not detected by this analysis consists mainly of tertiary and quaternary carbon atoms in cyclopentyl and cyclohexyl rings. ACKNOWLEDGMENT
The author gratefully acknowledges his indebtedness t o R. W. Schiessler, under whose direction most of the pure hydrocarbons used in this investigation were synthesized, to J. E. Scardefield who assisted in obtaining the spectral data, to J. H. Matheny
who made the least squares calculations, and to L. C. Roes8 for helpful discuseiom of the work. LITERATURE CITED
(1) Anderson, J. il., Jr., and Seyfried, W. D., ANAL.CHEM.,20, 998 (1948). (2) Evans, Albert, Hibbard, R. R., and Powell, A. S., Ibid., 23, 1604 (1951). (3) Grubb, H. M., private communication. (4) Hastings, S. H., and Anderson, J. -4., Jr., “Determination of
Normal -41kyl Side Chains by Means of Infrared Spectroscopy, Pittsburgh Conference on Analytical Chemistry and A~uliedSuectroscow. March 1951. (5) Hast:ngs, S.-H., WaGo;, A. T., Williams, R. B., and .knderson, J. -4., Jr., -4NAL. CHEM.,24, 612 (1952). (6) Hibbard, R. R., and Cleaves, A. P., Ibid., 21, 486 (1949). (7) McMurry, H. L., and Thornton, Vernon, Ibid., 24, 318 (1952). (8) Oetjen, R. A., J . Opt. SOC.Amer., 35, 743 (1945). (9) Rose, F. W., J . Research .Vat2. Bur. Stalkdarda, 20, 129 (1938). (10) Sachanen, -4. Tu’., “Chemical Constituents of Petroleum,” Chap. 4 , Xew York, Reinhold Publishing Carp., 1945. (11) Smith, D. C., “Infrared Spectra of Pure Hydrocarbons,” Naval Research Laboratory, Rept. C-3274 (1900). RECEIVED for review June 1, 1953. Accepted July IO, 1953. Presented io part at the Pittsburgh Conference on .4nalytical Chemistry and bpplied Spectroscopy, Pittsburgh, Pa., March 1952.
Infrared Band Correlations for Some Substituted Olefins ROBERT E. KITSON’ Polychemicals Department, Research Division, E. I . du Pont d e Nemours & Co., Inc., Wilmington, Del.
The infrared spectra of more than 100 substituted olefins, principally halo- and cyano-olefins, were measured. The absorption bands due to the out-ofplane bending vibrations of the ethylenic hydrogen were studied, and their positions in such molecules compared with their position in hydrocarbons. Substitution in vinyl and vinylidene compounds produced little change in the band position as compared with the corresponding hydrocarbons, except when the substituent was conjugated with the double band. In molecules of the type transRCH=CHX, however, the band was shifted from 10.36 to 10.74 microns when X was chlorine or bromine. Substitution in the alkyl groups of the cis-
r
THE infrared spectra of many olefinic compounds are charac-
. . terized by one or two intense absorption bands in the region oi 11 microns. In recent years, the significance of these bands, due to the out-of-plane bending vibrations of the ethylenic hydrogen atoms, and their relation to the structure of olefins have been recognized and reported ( 1 ) . In the past few years, this laboratory has recorded the infrared spectra of more than 100 substituted olefins, principally halo- and cyano-olehs of three to five carbon atoms. T hispaper presents the effect of such substituents on the out-of-plane bending vibrations and the presence of other bands which may be characteristic of these compounds.
RCH=CHR’ structure shifted the band from its position in hydrocarbons (14.0 to 14.7 microns) to a value around 13.3 microns. A sharp, intense band at 8.01 microns was found in molecules having the group RR’C=CHCHzCI. The corresponding bromine and iodine compounds have bands at 8.30 and 8.70 microns. The band was shifted to 7.94 and 8.25 microns in the chlorine and bromine compounds when the ethylenic hydrogen was replaced. Through the use of these modifications and extensions to the normal hydrocarbon band assignments, it has become relatively simple to establish the position and type of ethylenic double bond from the absorption spectrum of an unknown halo- or cyano-olefin.
beam) instruments being used. Sodium chloride optics were use in most cases. The wave-length calibration of each spectrometer was carefully checked and believed to be accurate within ltO.01 micron in the region from 8 to 15 microns. The samples were mounted, as liquids or as carbon disulfide solutions, in fixedthickness sodium chloride cells. The known compounds were accumulated from a number of sources. Some were obtained from commercial sources, othere were synthesized in various Du Pont laboratories, and still others were supplied by L. F. Hatch, University of Texas. The spectra (from 2 to 15 microns) of many of the latter compounds have been published by Hatch and his students ( 4 ) .
EXPERIMENTAL
Infrared measurements were made with Perkin-Elmer spectrometers, both the Model 12 (single-beam)and Model 21 (doublePresent address, Textile Fibers Department, Nylon Research Division, Carothers Research Laboratory, E. I. du Pont de Y e m o w & Co., Inc., Wilmington, Del. 1
DISCUSSION
In any infrared band correlation study, some consideration must be given to band intensity. If a sufficiently thick sample is examined, a small band can be observed a t or near almost any desired wave length between 7 and 15 microns. Consequently,
V O L U M E 25, NO. 10, O C T O B E R 1 9 5 3
1471
great care must be used in assigning significance to an absorption band. In this work, no attempt was made to measure band intensities quantitatively. Bands were classed as intense which gave fairly strong bands (absorbance > 0 . 5 ) when observed in 10% solutions in 0.030 to 0.050-mm. cells. Under these conditions most of the compounds examined showed four to six bands in the range from 3 to 15 microns and their significance could not be queptioned. BAXDS DUE TO OUT-OF-PLANE BENDING
Table I summarizes the experimental data obtained on the infrared absorption bands due to the oubof-plane bending vibrations. Column 2 lists the positions of these bands in hydrocarbons as reported by Anderson and Seyfried (1). Column 3 gives the number of compounds of each type studied and column 4 gives the average band position and the observed average deviation. RCH=CH2. In general, the bands in substituted vinyl compounds of this type are sharp and very similar to the corresponding bands in hydrocarbons. Simple substitution, as in 3-chloro1-butene or 3,4-dichloro-l-butenr, tends to shift the bands closer together and to increase slightly the range over which they are found. If the substituent contains a group which can conjugate with the double bond, or if the substituent is an alkoxy group, the band shapes and positions are completely changed. Stroupe has described ( 5 ) the correlations which exist in polar olefins such as the vinyl ethers and vinyl ketones.
Table I. Position of Out-of-Plane Bending Vibration Band and Correlation of Structure in Substituted Olefins Position of .4bsorption Band S o . of Halo a n d cyano comsubstituted pound~ hydrocarbons, examined microns
-
Type of Compound’ RCH=CH*
Hydrocarbonsb, Microns 10 05 &
0 02 & 0.02 11.24 i 0.02
20
10.98
......
10.36 f 14.0 11.9
0.02
...... ......
- 14.7
-
12.7
2; 14 7
2 11
10 15 10.80 11.16 10.63 10.36 10.74 10.4 13.9 11.9
*zt
0.05 0.06 i 0.11 i 0.05 i 0.04 f 0.03 10.5 - 12.7 - 12.7
-
a R, R‘, R ” = alkyl groups (column 2) or substituted alkyl group3 (coliiiiin 4). From Andemon a n d Seyfried (I).
RR’C===CH,. In compounds of the RR’C==€H2 type. there exist several structural possibilities: One or both of the R groups may be substituted, or one of them may be a substituent such as a halogen atom or a nitrile group. (KO compounds having only two carbon atoms were included in this work.) The nature of the substitution does not seem to affect the band greatly, except for R = -CN or -C=O. The average position of the band is shifted only slightly from its position in the corresponding hydrocarbons. It occurs over a somewhat greater range, being found as high as 11.4 microns in Zchloro-1,3-butadiene and as low as 11.0 microns in 2,3,3-trichloro-l-butene. If R = -CN or =0, as in methacrylonitrile or methyl methacrylate, the band is found uniformly a t 10.6 microne. Conjugation with other C=C groups does not seem to affect the band position.
>c:
trans-RCH=CHR’. Several -trurtui a1 possibilitiee also mist in compounds of the type RCH=CHR’, and different band positions are observed in some cases.. When R and/or R’ is a substituted alkyl group, as in trans-1-chloro-2-butene or trans-1,4dichloro-2-butene, the band occurs a t almost exactly the same place a3 in hydrocarbons, although the average deviation is slightly greater. If, however, one of the 11’s is a halogen atom, as in 1-chloro-1-propene, the b:md is found m a r 10.74 microns. Its shape iq c*hangrdsomewhat, and, in some cases, a small, unresolved hand appc>arson the high-1%ave-length side of the major band. Since this observation was made, Haszcldine ( 3 ) has reported thr position of this band in a number of substituted olefins. Hc obsc~i-vedthr wide vaiiations between the two types of compounds RCH=CHR‘ and RCH=CHX, but did not attach any pa~tirulaisigiiificancc to it. His data fall in line with the author’s obsrrvationq.
Table XI.
Position of Characteristic Band in Structure CRR’=CYCHzX s o . of Examples
Band Position
The effect of conjugation on this band I $ iiot so clear as in the preceding case. Two compounds involving >C=O (2-butenoic acid and 2-buten-1-al) show the band a t about 10.30, an apparently insignificant shift. Two other compounds were available where R is -CN, and here the band appeared at about 1045 microns, which may be significant. Bands due to the preceding types of unsaturation are sharp, intense, and readily located in the spectrum of a molecule. This is unfortunately not true of the remaining types of unsaturation. cts-RCH=CHR‘. The hands due t o the cis-internal double bond structure are broad, less intrnse, and somewhat variable in position. Furthermore, fewer reliablr samples with this structure are available In straighbchain hydrocarbons, the band due to this structure appears between 14.0 and 14.7 microns. Hall and hfikos ( 2 ) have pointed out that branching of one or both R groups shifts the band to a position helon 14 microns. A similar shift is observed h y substitution of a halogen atom on one or both R groups In cis-l-chloro-2-butene, the band appears a t 13.0 microns, and the author has ohscrved it as low as 12.7 microns (in czs-l.4-dirhloro-2-butene). Where one of the R’s is a halogen or a nitrile, the band is also found b(~10n-14 microns, but no differentiation can be made among thr various structural powihilities on tht. basis of the examples studied. RR’C=CHR”. With compounds ot the type RR’C=CHR ”, the bands are even weaker and more difficult to assign. This is particularly true of chlorinated olefin.;. M here bands in the rrgion from 11.5 to 13.0 microns appear vhich are due to other modes of vibration. About 25 such compounds were examined in the course of this study. Where definite assignments could be made, substitution of a halogen or a nitrile group had little effect on the band’s position as compared to hydrocarbons. OTHER BANDS
RR’C=CR’’R”’. Olefins of this type, having no ethylenic hydrogens, have no absorption bands corresponding to those described above. The spectra of four compounds of the type CHsCR=CRCH, n here R=CHI, C1, Ur, or C N all show a moderately strong band between 8.6 and 9.4 microns. Substitutioii of a chlorine or a hydroxyl group on one of the methyl groups in the
ANALYTICAL CHEMISTRY
1472 Table 111. Band Positions in Compounds of Types CHCl=CY-CHzX gnd CC12=CY-CHZXa Y= H
F
C1
H F High boiling Low boiling CI High boiling Low boiling
No. of Compounds
c=c,
Microns
4 6.11-6.16 4 5.97-6.01 3 6.17-6.24 CHCI=CT-CH,X“ 4h 6.10-6.15 3 5.90-5.95 3
3 3
5.93-5.98 6.05-6.19 6.08-6.19
Unknown Band, Microns 11.37-11.75 10.20-10.35 10.82-10.95
11,2S-ii. 32
12.10-12.15 10 96-11.10 11.85-11.93 12.17-12 32
= H , CI, Br, or OH. * XIncludes both cis- and trans- isomers
a
chlorinated compound, to produce 1,2,3-trichloro-2-butenc or 2,3-dichloro-2-butene-l-ol, destroys the band. This suggests it may be due to the symmetry of the molecule. RR’C=CH-CH,X. I n the spectra of seveial of the chloroolefins, a single, sharp, strong band was observed a t 8.01 microns. The intensity of the band and its constancy of position attracted attention. A careful study was made of the spectra of all the defins available in an effort to establish its source. The band appears in 3-chloro-1-propene and I-chloro-2-butene. In the corresponding bromides it is shifted to about 8.30 microns (Table 11). I n 3-iodo-1-propene it is found a t 8.70 microns I t is now apparent that this band occurs in the spectra of all molecules having the structure RR’C=CH-CH2X. Its exact position depends on whether X is chlorine, bromine, or iodine. The nature of R and R’ does not seem to affect the band, since it occurs in the spectra of such molecules as 1,3-dichloro-2-butenej where R and R’ are a chlorine and a methyl, respectively, in 1,1,3-trichloro-lpropene, where R and R’ are both chlorine, and in 3-chloro-lpropene, where R and R ’ are both hydrogen. Substitution of one of the terminal hydrogens destroys the band or reduces its intensity and shifts its position. For example, i t is found as a weak band a t 8.13 microns in 3-chloro-1-butene. Replacement of the ethylenic hydrogen atom with another atom or group shifts the position of the band somewhat. The nature of the substituent does not seem to make much difference, although this observation is based on a small number of groups (chlorine, fluorine, methyl, and phenyl). The band occurs a t 7.94 microns in the chlorine compounds and a t 8.25 microns in the corresponding bromine compounds. Two compounds were available which contained both groupd ( 1,4-dichloro-2-methy12-butene and 1,2,4-trichloro-2-butene), and the spectra of each show both bands. Elimination of the hydiogen altogether, to form the corresponding acetylenic compounds, appears to have less effect on the band but its position is still lorn-ered somewhat. The band is found, for example, a t 8.28 in 3-bromo-1-propene and a t 8.26 in 3-bromo1-propyne. I n 1,4-dichloro-2-butene and 1,4dichloro-2-butyne, the corresponding values are 8.01 and 7.96 microns The band does not occur in the corresponding alcohols or nitriles. No fluorine compounds of this structure were available for study. Some care must be exercised in using this band for structure work, since many halo-olefins have bands in this region of the spectrum, Where the assigned structure is not involved, however, the bands are usually numerous and/or relatively weak. Other Correlations. The spectra of the compounds available were examined for other possible correlations. So far, no completely general correlations have been found, but some interesting observations were made on the spectra of propenes of the types CHCI=CY-CH*X and CCIZ=CY-CHgX, where Y may be hydrogen, chlorine, or fluorine and X may be hydrogen, chlorine, bromine, or hydroxyl. Most of these compounds were supplied by Hatch and his coworkers (4).
Two points of interest were noted in these compounds. First, the 1,l-dichloro compounds all show sharp, intense bands in the region of 10 to 11 microns. The position of these bands correlates with the nature of Y but is independent of X (Table 111). I n the corresponding 1-chloro compounds, bands do occur where Y is fluorine or chlorine which can be correlated with Y in a similar manner, but they are neither as strong nor as sharp as in the 1,l-dichloro case. They are also listed in Table IV, but their significance is doubtful. The second point of interest is the effect of Y on the position of the C=C stretching frequency. iis shown in Table 111, if Y is a fluorine atom, the C=C stretching vibration comes at a markedly lower wave length (higher frequency) than if Y is hydrogen or chlorine. C-CI Stretching Bands. The bands which are found between 12 and 15 microns in the spectra of the chloro-olefins were studied carefully to determine whether any correlation existed between band position and the location of the chlorine atom. None could be found. Typical of the problem are the various 1,4dichloro-C4 compounds. Seven such compounds were available. The compounds and bands in their spectra between 12 and 15 microns are listrd in Table IV. I t seems obvious that there is no correlation here. Similar attempts throughout the group of compounds were fruitless.
Table IV.
Position of Bands in 1,4-Dichloro-C~ Compounds”
Compound
Xlicronr
1,4-Dichloro-2-butene (cis) (trans) 1,4-Dichloro-2-butyne
1,4-Dichloro-2-methyl-2-butene 1,2,3,4-Tetrachlorobutane(meso)
12.2 (w) 12.75 12.95 (sh) 13.35 (w, bri 12.70 (opb) 14.0 12.75 (w) 14.13 12.75 (w) 14 1 @P) 13 71 15 1 12.6 w) 1 3 . 0 lw) 13 57 i 3 80
a w = weak, br = broad, sh = shoulder, opb = out-of-plane bending vibration.
ACKNOWLEDGMENT
The author is indebted to many people for assistance in this work: to L. F. Evans, who purified many of the commercial samples studied; to other Du Pont chemists, who made available samples of hard-won compounds; to Lewis F. Hatch and his students a t the University of Texas for the many unique and pure samples they provided; to R. C. Voter of this laboratory, who first noted the shift of the RR’C=CH2 band caused by conjugation; and to the other members of the Polychemicals Research Division Infrared Laboratory who obtained most of the original spectral data. LITERATURE ClTED
(1) Anderson, J. A., and Seyfried, W. D., AX.*L. CHEM.,20, 998 (1948). (2) Hall, H. J., and Mikos, I. S., Ibid., 21, 422 (1949). (3) Hasaeldine, R. N., J . Chem. Soc., 1952, 2504. (4) Hatch, L. F., et al., J . Am. Chem. Soc., 73, 4393 (1951); 74, 123, 2911, 3328 (1952). (5) Stroupe, I. D., and Clement, L. A., “Infrared Spectroscopy of Polar Olefins,” presented a t Symposium on Molecular Structure and Spectroscopy, Columbus, Ohio, June 9 to 13, 1952. R E C E I V Efor D review March 28, 1953. Accepted July 23, 1953. Presented in part before the Division of Analytical Chemistry a t the 121st Meeting ot the ERICAS AS CHEIIICALSOCIETY, Buffalo, s.Y.
