benzene but not, styrene or phenylacetylene. The chromatogram of a combustion sample from an internal combqstion engine as shown in Figure 5 also indicates a composite fourth major peak. Chromatographing a n ozonized aliquot results in a great reduction in the peak area of the fourth major peak. If propylbenzene is not produced in measurable quantities during combustion, there is an indication that the relative concentration of propylbenzene in atmospheric samples may indicate the relative contribution of internal combustion sources to the atmosphere. Work is being continued
on this over-all aspect to determine the complete significance. ACKNOWLEDGMENT
The laboratory assistance of Toshio Kat0 and P. S. Snyder is acknowledged. LITERATURE CITED
(1) Altshuller, A. P., Clemons, C. A.,
ANAL.CHEM.34, 466 (1962). (2) Leach, P. W., Leng, L. J., Bellar, T. A., Sigshy, J. E., Jr., Altshuller, A. P., J. A i r Pollution Control Assoc. 14. 176 (1964). ( 3 ) ort timer, J. V., Gent, P. L., Nature 197, 789 (1963).
(4) Mosher, W. A., Advances in Chemistry, No. 21, p. 141, ACS, Washington, D. C., 1959. (51 ~, Mukai. M.. Tehhens. B. D.. Thomas. J. F., ANAL’CHEM.3 6 , 1126 i1964). RECEIVEDfor review October 19, 1964. Accepted January 4, 1965. This work received the support of research grant, AP-00275-01 of the Division of Air Pollution, Bureau of State Services, Public Health Service and is a cooperative effort within the University of California of the School of Public Health and the Sanitary Engineering Research Lahoratory, Department of Engineering. Division of Water, Air, and Waste Chemistry, 148th Meeting, ACS, Chicago, Ill., September 1964.
NucIear Magnetic Resonance Spectra-Structure Correlations for Chlorinated 2,2-DifIuoropropa nes HORACE
F. WHITE
Research and Development Department, Chemicals Division, Union Carbide Corp., South Charleston, W . Vu. The nuclear magnetic resonance spectra of a series of terminal chlorinated 2,2-difluoropropanes have been studied. Proton functional group chemical shifts are correlated with the sum of electronegativities of the nonskeletal atoms and are found to change predictably with varying nonadjacent substituent. The F19 spectra, while first-order and related to the proton spectra, show no correlatable shift property. Protonfluorine coupling constants do vary with molecular composition and are related to the proton-tofluorine dihedral angle in a manner analogous to the dependency others have established for fluoroethanes.
T
terminal chlorination of 2,2-difluoropropane has resulted in a series of compounds similar to those recently discussed ( I d ) . These novel compounds have been identified by nuclear magnetic resonance spectrometry through the use of a correlation diagram also similar to those recently published (18). F19 resonance patterns and proton-fluorine couplings have been valuable adjuncts in assigning structures to these molecules. HE
EXPERIMENTAL
Proton resonance spectra were obtained on a Varian Model A60 spectrometer and are of 10% by liquid volume solutions of solute in carbon tetrachloride. A few drops of tetramethylsilane were placed in each sample tube for internal reference. Resonance shifts were recorded to the nearest 0.3 cycle and converted to chemical shifts in parts per million by the usual method (IO).
Fluorine resonance spectra of all samples were obtained at 56.4 megacycles on a Varian Model 4300-B high-resolution spectrometer equipped with a field homogeneity control unit. The materials were scanned as 10% b y liquid volume solutions in carbon tetrachloride and, when possible, as pure liquids; in either case, a small amount of fluorotrichloromethane was added to each sample tube for internal fluorine resonance reference (6). Chemical shifts and coupling constants were determined by the usual side-band modulation technique using a HewlettPackard Model 200-CDR audiooscillator and measuring the side bands with a Hewlett-Packard Model 524-D electronic counter. The various samples exhibit a different degree of shift on dilution with carbon tetrachloride; the 10% solution shifts are considered equivalent to infinite dilution shifts at the reported accuracy. RESULTS A N D DISCUSSION
Proton Spectra. Qualitative analysis of products produced in t h e terminal chlorination of 2,2-difluoropropane has been facilitated by the development of a correlation between proton chemical shift and propane substituent electronegativity (9) found to exist in analogous materials (12). Figure 1 shows the correlations produced from the compounds listed in Table I. These graphs differ from the previously discussed correlations (12) in that all the variations are linear not only among the molecular series but also within the end groups. While the proton spectra of some molecules (3) show very fine structure, second order effects (IO), the F19resonance patterns (at the resoIution used) were simple, first-order spectra;
therefore, the second-order splittings were ignored in the preparation of the proton correlations. Fluorine Spectra. FI9 spectrastructure correlations have been discussed by several authors (1, 4, 5 , I I ) , and these discussions have shown that the Fl9 chemical shift is related to the molecular environment. For these molecules, a linear relationship between chemical shift and propane substituent electronegativity (9) does not exist. However, in general, the FI9 resonance shifts to higher fields with increasing substituent electronegativity; such a higher field shift is exactly opposite to the proton shift. The resonance positions given in Table I are the algebraic mean of the individual line positions and the spectra are simple, firstorder patterns. Coupling Constants. Protonfluorine coupling constants have also been included in Table I . These values were derived primarily from t h e FI9 spectra and agree to 0.1 cycle with the main s p l i t t i n g observed in the proton spectra. I n Figure 2, the observed constants are plotted against carbon substituent electronegativity in a manner analogous to the chemical shifts. Such a correlation allows the prediction of coupling constants for the two unavailable members of this series (7.0 and 13.3 C.P.S. for CHC1&F2CH2C1 and 12.4 c.p.s. for CH2C1CF2CH2C1). Gutowsky ( 7 ) and Karplus (8) have discussed the dependency of coupling constant on dihedral angle between coupled atoms for proton-proton and proton-fluorine couplings in ethanic and ethylenic compounds. Anet ( 2 ) VOL. 37, NO. 3, MARCH 1965
e
403
.
o OBSERVED RESCNANCES A FREMCTEO RESONANCES
r
249,
/
CHCl2CF2CHCl2
,
P
CHZCICFZCC13
-
b
I
CHzCICFz CHZCI
P
21 3
CHZ RESONANCES
204
20.4
< 2
I I Ck, IO 15 PROTON FLUORINE COUPLING CONSTANl (CYCLES PER SECOND)
5
19.5 2.0 2.5 30 3.5 4.0 4.5 5.0 5.5 6.0 6 5 PROXW C H E M W SHIFT (WRTS PER MILLION FROM TETRAMETHYLSILANE) 1.5
Figure 2. Variation in H-F coupling in CH,CI,CF,CH,CI,
Figure 1 . Variation of proton chemical shift in CHzCIvCF&HmCIn
x + y = 3 = m + n
x + y = 3 = r n + n
has extended the proton-proton dependency to include ring systems, while Elleman, Brown, and Williams (5) have substantiated the proton-fluorine results with ranges for H-F coupling constants for many fluorocarbons. However, an angular dependency has not been explicitly demonstrated for the H-F case as it has been for the H-H couplings. The present study offers an opportunity for investigating such a n
Table 1.
angular dependency in some saturated fluoropropanes. When a molecular model of 2,2difluoropropane is viewed along one carbon to carbon bond, it is seen that the three methyl protons in the staggered configuration are all equivalent with respect to the two fluorine atoms. Similarly viewing the methylene protons of the monochloro compound shows the most favorable position to be
Observed Chemical Shifts and Coupling Constants for Halogenated Propanes
Sum of electroCoupling constantsd negativities of Proton chemical shift' Fluorine Fluorine Fluorine substitMethchemical to t o nonCompound u e n t s ~ Methyl ylene Methine shift0 methyl methyl CH3CFzCHa 20.4 1.61 ... ... 85.04 17.76 CH3CFzCHzCl 21.3 1.76 3.66 ... 94.90 17.92 ii:4i CHsCFzCHC12 22.2 1.88 ... 5.77 97.97 17.84 5 85 CH3CFzCClg 23.1 2.07 ... ... 99.95 17.42 CHzClCFzCCl, 24.0 ... 4.30 ... 110.60 .,. 14:20 CHClzCFzCHC12 24.0 ... ... 6.24 117.44 .., 8.74 CHClzCFzCC13 24.9 ... ... 6.47 106.49 .,, 9.23 Pauling's electronegativities; F = 3.9; C1 = 3.0; H = 2.1. Chemical shifts in parts per million to lower field from tetramethylsilane internal standard. Chemical shifts in parts per million to higher field from fluorotrichloromethane internal standard. Coupling constants in cycles per second: values obtained from dilute solution mensurements. -
protons opposed to fluorines (cis), while the methine proton of the dichloroderivative would most likely be gauche to both fluorine atoms. Figure 3 shows the dependency obtained when the above assumptions of molecular geometry are plotted against coupling constant. The methyl group is assumed to be in the staggered position, with the coupling constant derived from the nondigauche protons. I n Figure 3 the digauche dihedral angle has been chosen as the origin. Table I1 summarizes the assumptions used in preparing Figure 3 as well as the dihedral angles derived from the coupling constants of the higher molecular weight members of this series. Also included in Table I1 are the coupling constants predicted from Figure 2 for the unavailable molecules and their dihedral angles predicted from Figure 3. The data presented graphically in Figure 3 agree with the ranges calculated by Karplus (8) for cis and trans H-F coupling constants.
(I
Table II.
Coupling Constants and Dihedral Angles for Halogenated Propanes
Coupling constants" Fluorine to Fluorine to Compound methyl nonmethyl 17.76c 17.92~ ii.ii' 17.84~ 5.85 17.42~ ... 14.20' ... 8.74 ... 9.23 ... 12.4. ... 13.3;7.00 a Coupling constants in cycles per second. Dihedral angle measured from digauche configuration. Average to 17.7c.p.s. for 120' configuration. Assumed from inspection of models. e Predicted from Figures 3 and 4.
404
ANALYTICAL CHEMISTRY
Dihedral H,C.C.F angle * 120"d 60°d OOd
... 84e 326 368 688 76, 1 4 ~ 0 IDGAUCHE)
€0 I20 180 (DEGREES FROM (CIS) (STAGGERED) DIGAUCHE)
ROTATION ABOUT C-C BOND
Figure 3. Variation of H-F coupling with dihedral angle
ACKNOWLEDGMENT
The author thanks V. 4.Yarborough for his continuing interest and stimulating discussions during the course of this investigation. LITERATURE CITED
(1) Alley, S. K., Jr., Scott, R. L., J . Chem. Eno. Data 8. 117 (1963). ( 2 ) Anet, F: A. L., ‘Can. J. Chem. 39,
789 (1961). (3) Bhacca, S . S., Hollis, D. P., Johnson,
L. F., Pier, E. A,, “N.M.R. Spectra Catalog,” Vol. 2, No. 381, Varian Associates, Palo Alto, Calif., 1963. ( 4 ) Brame, E. G., ANAL.CHEM.34, 591 (1962). (5) Elleman, D. D., Brown, L. C., Williams, D., J . Mol. Spectry. 7, 393 (1961). (6) Filipovich, G., Tiers, G. V. D., J . Phys. Chem. 63, 761 (1959). (7) Gutowsky, H. S., Pure A p p l . Chem. 7, 93 (1963). (8) Karplus, M., J. Chem. Phys. 30, 11 (1959). (9) Pauling, L., “Nature of the Chemical
Bond,” p. 58, Cornel1 University Press, Ithaca, N. Y., 1940. (10) Pople, V. A., Schneider, W. G., Bernstem. H. J.. “Hizh-Resolution Nuclear ’Magnetic Resckance,” pp. 87, 130, 151, McGraw-Hill, New York, 1959. (11) Smith, T. S., Smith, E. A., J. Phys. Chem. 63, 1701 (1959). (12) White, H. F., ANAL CHEM. 36, 1291 (1964). RECEIVED for review November 27, 1964. Accepted January 7, 1965. Division of Analytical Chemistry, Southeastern Regional Meeting, ACS, October 1964.
Refractive Indices of Sucrose-Water Solutions in the Range from 24 to 53% Sucrose D. F. CHARLES California and Hawaiian Sugar Refining Corp., Crockeff, Calif.
b The presence of a dip in the refractive index curves currently proposed for official acceptance b y the International Commission for Uniform Methods of Sugar Analysis suggested some inconsistencies calling for resolution. Measurements were made of refractive index for sucrose-water solutions between 22 and 59% sucrose, covering the range in question. Results are tabulated. The new values appear to produce a consistent and smooth curve when compared with Landt-Schonrock data between 0 aqd 25y0 sucrose and Snyder and Charles data above 50% sucrose, but they deviate from the International scale values, giving refractive index higher by 14 X 1 0-5 unit near 4Oy0 sucrose. The calculation of a consistent fiveplace sucrose refractive index table now appears possible.
I
1936 the International Commission for Uniform Methods of Sugar ilnalysis (6) adopted officially the International scale of refractive indices. This scale was a composite of results of at least three separate investigations. Below 24% solids Landt ( 7 ) had shown good agreement between his results and Schonrock results of 1933 (apparently unpublished). Therefore, the official scale was carried to five decimal places in this region, using the Schonrock data as listed by Landt (7‘). Above 71Yob,data of Main ( 8 ) were used. Between 24 and 66%, Schonrock data of 1911 ( 2 1 ) were used, with a straight line interpolation from 66 to 71%. Because of discrepancies and uncertainties, the table carried only 4 places in refractive index (R.I.) above 24y0 solids. N
Subsequent investigations, in particular those of Snyder (18) and Charles (2), indicated significantly higher refractive indices than those of the International scale of 1936 in the commercially important range above 5Oy0 sucrose. Hill and Orchard (4) presented a statistical appraisal which showed the Snyder and Charles results in good agreement for the concentration range of 53 to %?yo’,. Still later Hill and Orchard ( 5 ) and Charles (3) discussed the problem of relating the new data in the upper concentration range to the International scale values for lower concentrations to produce a smooth and continuous variation. The Hill and Orchard (5) mathematical smoothings and the Charles graphical smoothing (3) are in substantial agreement. Following a suggestion of Van Hook ( I S ) , Charles (3) prepared a plot of ( N - N o ) / C which showed a dip in what otherwise might be a smooth curve joining the Landt data in the range of 0 to 24% solids (6) with the Charles-Snyder data above 53% solids (4). T o verify if such a dip was real, a further series of determinations was made and is the subject of this paper. PROCEDURE
Solutions were prepared in ground glass-stoppered Erlenmeyer-shape weighing bottles. The sugar used was a high purity commercial sucrose, confectioner’s sanding. Weights of the crystalline sugar were corrected for 0.060yGinternal moisture as determined by Onna (9) as well as for 0.003% external moisture as determined by drying of air-equilibrated sugar a t 70’ C. under vacuum. Total impurities in the sugar, aside from moisture, were of the order of 0.01%.
Refractive indices were read on a Bausch and Lomb precision sugar refractometer (Catalog No. 33-45-91, serial No. XD7176, prism series 719). Readings made on the arbitrary linear scale were corrected to 20’ C. Neasurement techniques and temperature corrections were as discussed by Charles and Meads (14). Corrections were applied based on a concurrent series of distilled water readings. An additional correction was based on readings of a triangular test plate certified by the National Bureau of Standards to have a refractive index of 1.46632. The scale error at this point averaged $0.014 scale unit, equivalent to 0.000041 unit of refractive index or O.OIS~Osucrose. The corrections were assumed linear in scale units between the water reading and the glass plate reading at 1.46632
R.I.
RESULTS A N D DISCUSSION
Table I shows per cent suclose by weight in air and corresponding refractive index determined experimentally. The third column lists values of the function ( N - N o ) / Cas suggested by Van Hook (13) and discussed in a previous paper (3). Values of C were computed from Table 113 of Bates ( 1 ) . The refractive index of water, N o , was taken to be 1.33299 as in the Bates table. Because N - N o / C is so nearly constant, a graph of this function against C serves to magnify the effects of small differences in refractive index. Figure 1 illustrates that the new data deviate significantly from the values of the 1936 scale. Further, as shown by the dashed curve, the new data bridge the gap more smoothly between the fiveplace Landt figures (6) and the SnyderCharles data (4). VOL. 37, N O . 3, MARCH 1965
405
