Symmetrically Substituted Dihalobiphenyls (LiH) is quite close to the total Eeot of 0.0833 ciated with the Li+ and H" ions.
au asso-
IV.
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Summary The influence on the electron density of correlation effects inherent within each of two correlated wave functions has been investigated for LiH. A natural orbital analysis provided a first natural configuration which was used as a noncorrelated limit. Charge movements were illustrated by means of density difference maps and profile diagrams. The wave functions examined were those of Palke and Goddard and of Bender and Davidson which recovered, respectively, about 36% and 89% of the correlation energy for LiH.
421
Briefly, although the introduction of correlation effects caused the charge cloud to expand in both calculations, the Palke and Goddard calculation overemphasized the effect by comparison with the Cl treatment. This conclusion parallels a similar situation found for atoms. Within the framework of our analysis, electron correlation increased the density at each nucleus and also reduced the charge in the internuclear region. Further, in the vicinity of the nuclei, the charge redistributions exhibited characteristics of split-shell correlation similar to those associated with two-electron ions. Although not part of this investigation, the study suggests some general support, for an Li+H~ interpretation of the bonding in LiH.
Nuclear Magnetic Resonance Spectra and Substituent Effects for
Symmetrically Substituted Dihalobiphenyls by A. R. Tarpley, Jr.,1 and J. H. Goldstein* Department of Chemistry, Emory University, Atlanta, Georgia
30322
(Received August 10, 1970)
Publication costs assisted by Emory University
Nmr spectra have been analyzed for the twelve symmetrically substituted dihalobiphenyls.
Additivity of substituent effects has been observed for coupling constants and chemical shifts. The effects of substituents on the coupling parameters have been shown to correlate quite well with substituent electronegativity, in agreement with previous work on disubstituted benzenes. Substituent effects on the chemical shifts have been discussed in terms of ring current modification in the second ring and in terms of other well-known mechanisms. Downfield shifts at certain positions have been attributed to steric interactions. An inter-ring seven-bond H-F coupling has been observed in the case of 4,4'-difluorobiphenyI but no such inter-ring coupling was found for 3,3'- or 2,2'-difluorobiphenyl.
Introduction Considerable interest has been directed toward obtaining and interpreting the nmr parameters of substituted benzenes.2-24 Many of these studies have been concerned with additivity of substituent effects on coupling constants and chemical shifts, demonstrating the great utility of additivity values in the analysis and assignments of aromatic nmr spectra. Improvements in spectrometer performance and the availability of high-speed, iterative computer programs for nmr spectral analysis have greatly facilitated the study of these spectra and the resulting very precise values from these analyses have made the study of substituent effects much more reliable. Following the example of previous work,22·23'25-86 statistical correlations between substituent electronegativity and nmr coupling param-
eters were established in monohalo- and dibalobenzenes86 where the changes in coupling values with sub(1) NDEA Fellow, 1967-1970; 1971.
Tennessee Eastman Fellow, 1970-
(2) (a) . L. Corlo and B, P. Dailey, J. Amer. Chem. Soc., 78, 3043 (1956); (b) J. B. Leane and R. E. Richards, Trans. Faraday Soc., 55, 707 (1959). (3) I. Yamaguchi and N. Hayakawa, Bull. Chem. Soc. Jap., 33, 1128 (1960). (4) P. Diehl, Helv. Chim.
Ada, 44, 829 (1961).
(5) H. Spieseeke and W. G. Schneider, J. Chem. Phys., 35, 731
(1961). (6) J. C. Schug and J. C. Deck, ibid., 37, 2618 (1962). (7) J. Martin and B. P. DaUey, ibid., 37, 2594 (1962). (8) J. S. Martin and B. P. DaUey, ibid., 39, 1722 (1963). (9) S. Castellano and C. Sun, J. Amer. Chem. Soc., 85, 380 (1963). (10) T. K. Wu and B. P. DaUey, J. Chem. Phys., 41, 2796 (1964).
(11) S. CasteUano and J. Lorenc, J. Phys. Chem., 69, 3552 (1965). The Journal of Physical.Chemistry, Vol. 75, No. 3, 1971
422
A. R. Tarpley, Jr., and J. H. Goldstein
stituent
are relatively small. Substituent effects on chemical shifts have been treated in general by Dewar, et aZ.,87-89 while other workers have been concerned with substituted benzenes.8'10-18·24 Extensive correlations have been obtained relating ortho effects of the substituent with the parameter q.immmo-44 Recently, substituent effects on chemical shifts have been discussed for various substituted biphenyls.46-46 In this article the results of nmr spectral analyses for the twelve symmetrically substituted dihalobiphenyls are given, all carried out under uniform experimental conditions. The analyses were greatly simplified by the availability of nmr analyses for biphenyl15 and the monohalobenzenes.16 -17 It was found that the assumption of additivity of substituent effects between biphenyl and the monohalobenzenes provided very useful initial parameters for these analyses. Coupling parameters for this series of compounds are shown to correlate quite well with substituent electronegativity values. Substituent effects on the chemical shifts are discussed in terms of well known mechanisms, particularly steric interactions at crowded positions. An inter-ring seven-bond coupling has been found for 4,4'difluorobiphenyl in several solvents.
Experimental Section
All compounds used in this study were the commercially available materials except 3,3 '-dichlorobiphenyl, 3,3'-dibromobipheny 3,3'-diiodobiphenyl, and 2,2'diiodobiphenyl which were not obtainable commercially and were synthesized in this laboratory. The commercial materials required no further purification, as indicated by their nmr spectra, except for 2,2'-diwas zone refined. A preliminary which fluorobiphenyl of the physical properties of these cominvestigation that indicated perhaps deuterated benzene pounds would be the only uniformly suitable solvent for the series because of the lack of solubility of some members of this series in other solvents. Normally an inert solvent such as cyclohexane is to be preferred here for studies of aromatic proton chemical shifts.43-44 However, as shown in Table VI, the substituent effects for adding the second ring to benzene, as in biphenyl, are roughly the same for the common solvents which have been used for work with biphenyls. In addition, the results in any one solvent should be internally self-consistent under uniform conditions and low concentrations. Therefore, substituent effects have been determined in the chosen solvent by obtaining the spectra of all relevant compounds under very uniform conditions. The samples were prepared as approximately 5 mol % solutions in C6D6 and were degassed with a stream of nitrogen. Approximately 1% TMS was added as an internal reference. 4,4 '-Dibromobiphenyl, 4,4'-dichlorobiphenyj, and 4,4 '-diiodobiphenyl were found to be relatively insoluble and were run as saturated solutions of 1-2 mol %. All spectra were recorded on a Varían 1,
The Journal of Physical Chemistry, Vol. 76, No. 3, 1971
A-60-A
spectrometer except fluorine spectra, which Bruker Scientific HFX-90 spectrometer. Calibrations were performed by the usual sideband technique using an audio oscillator constantly monitored by a frequency counter. The reported line frequencies are averages of at least three forward and three reverse traces and the mean deviation for a typical resonance line is approximately 0.05 Hz. All frequencies are referenced to the 1% internal TMS. 2,2'-Diiodobiphenyl was prepared from commercially available 2,2 '-dinitrobipheny via 2,2 '-diaminobiphenyl nmr
were recorded on a
1
(12) W. B. Smith and G. M. Cole, J. Phys. Chem., 69, 4413 (1965). (13) B. Dischler, Z. Naturforsch., 20, 888 (1965). (14) F. Hruska, . 2392 (1965).
M. Hutton, and T. Schaefer, Can. J. Chem., 43,
(15) R. E. Mayo and J. H. Goldstein, Mol. Phys., 10, 301 (1966). (16) J. M. Read, Jr., and J. H. Goldstein, J. Mol. Spectrosc., 23, 179
(1967). (17) J. E. Loemker, J. M. Read, Jr., and J. H. Goldstein, Mol. Phys., 13, 433 (1967). (18) W. B. Smith and J. L. Roark, J. Amer. Chem. Soc., 89, 5018 (1967). (19) T. Schaefer, F. Hruska, and . M. Hutton, Can. J. Chem., 45, 3143 (1967). (20) S. Castellano and R. Kostelnik, Tetrahedron Lett., 51, 5211 (1967). (21) R. W. Crecely, J. M. Read, Jr., R. S. Butler, and J. H. Goldstein, Spectrochim. Acta, Part A, 24, 685 (1968). (22) J. E. Loemker, J. M. Read, Jr., and J. H. Goldstein, J. Phys. Chem., 72, 991 (1968). (23) . B. Evans, Jr., A. R. Tarpley, and J. H. Goldstein, ibid., 72, 2552 (1968). (24) W. B. Smith, A. M. Ihrig, and J. L. Roark, ibid., 74, 812 (1970). (25) D. N. Grant, R. C. Hirst, and H. S. Gutowsky, J. Chem. Phys., 38, 470 (1963). (26) R. J. Abraham and K. G. R. Pachler, Mol. Phys,, 7, 165 (1964). (27) P. F. Cox, J. Amer. Chem. Soc., 85, 380 (1963). (28) A. D. Cohen and T. Schaefer, Mol. Phys., 10, 209 (1966). (29) S. Castellano and C. Sun, J. Amer. Chem. Soc., 88, 4741 (1966). (30) R. R. Fraser, Can. J. Chem., 44, 2737 (1966). (31) D. G. de Kowalewski and E. C. Ferra, Mol. Phys., 13, 547 (1967) (32) T. Schaefer and . M. Hutton, Can, J. Chem,, 45, 3154 (1967). .
(33) S. Castellano and R. Kostelnik, J. Amer. Chem. Soc., 90, 141 (1968) .
(34) S. Castellano,
R. Kostelnik, and C. Sun, Tetrahedron Lett., 46,
4635 (1967). (35)
K. Hayamizu and O. Yamamoto, J. Mol. Spectrosc,, 25, 422
(1968). (36) A. R. Tarpley, . B. Evans, and J. H. Goldstein, Anal. Chem., 41, 402 (1969). (37) M. J. S. Dewar and P. J. Grisdale, J. Amer. Chem. Soc., 84, 3539 (1962). (38) M. J. S. Dewar and P. J. Grisdale, ibid., 84, 3548 (1962). (39) M. J. S. Dewar and A. P. Marchand, ibid., 88, 354 (1966).
(40) J. L. Roark and W. B. Smith, J. Phys. Chem., 73, 1043 (1969). (41) J. L. Roard and W. B. Smith, ibid., 73, 1046 (1969). (42) W. B. Smith and J. L. Roark, ibid., 73, 1049 (1969). (43) B. Richardson and T. Schaefer, Can. J. Chem., 46, 2195 (1968). (44) T. Schaefer, B. Richardson, and R. Schwenk, ibid., 46, 2775
(1968). (45) Y. Nomura and Y. Takeuchi,
Tetrahedron Lett., 53 , 5585
(1968). (46) Y. Nomura and Y. Takeuchi, ibid., 54, 5665 (1968).
Symmetrically Substituted Dihalobiphbnyls Table I:
Substituent Contributions to Chemical Shifts and Proton-Proton Coupling Constants with Deuterated Benzene
Compd
Biphenyl Fluorobenzene Chlorobenzene Bromobenzene Iodobenzene «
423
,--:—-Substituent shift--. ,-Chemical Sm s„
-16.80 20.99 2.91
-6.09 -18.22
-3.17 14.00 18.53 23.40 30.72
as
Solvent
parameters®'6'6-—--.
couplings—---.
,-Proton-proton Sp
Sm
1.72 22.82 19.71 18.25 15.71
0.28 0.82 0.57 0.53 0.43
s,«
-0.10 -0.27 -0.24 -0.24 -0.25
-0.12 -0.31 -0.25 -0.27 -0.20
Su
Stt
-0.10 -0.06 -0.02 -0.05 -0.05
0.06 0.48 0.37 0.23 0.39
Sm
Sm
0.68 1.35 0.91 0.76 0.53
All values in Hz at 60 MHz. 6 Benzene, 5 mol % in CeDe, has a chemical shift of —429.00 Hz relative to 1% internal TMS. and Sij are as defined in ref 23.
0
S0,
Sm, Sp,
(prepared by the catalytic method of Ross, Kahan, and Leach47) according to the method described by Lothrop.48·49 The resulting material was recrystallized
from ethanol to an mp of 108°. The 3,3'-dichlorobiphenyl, 3,3'-dibromobiphenyl, and 3,3 '-diiodobiphenyl were prepared according to the method described by Snyder, Weaver, and Marshall.60 3,3'-Dichlorobiphenyl was recrystallized from ethanol and melted at 23-25°. 3,3'-Dibromobiphenyl was also recrystallized from ethanol and melted at 51-52°. It was necessary to purify the 3,3 '-diiodobiphenyl by column chromatography with the purified product melting at 58-59°.
Table II: Compd X =
J12
F Cl
Br I
8.58 (8.64) 8.40 (8.39) 8.38 (8.35) 8.25 (8.25)
Jit
2.75 (2.81) 2.36 (2.42) 2.43 (2.45) 2.44 (2.44)
2.56 (2.53) 2.37 (2.34) 2.19 (2.19) 1.98 (1.96)
0.37 (0.32) 0.42 (0.35) 0.42 (0.35) 0.38 (0.34)
Cl
Br
I
J
84
0.37 (0.32) 0.42 (0.35) 0.42 (0.35) 0.38 (0.34)
8.58 (8.64) 8.40 (8.39) 8.38 (8.35) 8.25 (8.25)
X
2
8.29 (8.26) 7.98 (8.01) 7.94 (7.97) 7.85 (7.87)
24
°
4
X
F
J
JM
J13
3
Analysis and Calculations All spectra were analyzed using an iterative computer program patterned after the Laocoon-II program of Bothner-By and Castellano.61 Trial parameters for the analysis of the monosubstituted halobenzenes and biphenyl in deuterated benzene were taken from previous work.15-17 In the disubstituted biphenyls, trial chemical shifts and coupling constants were calculated assuming additivity of substituent effects in biphenyl and the corresponding monosubstituted halobenzenes. As is customary for benzene derivatives62·63 all the proton couplings were assumed to be positive. In the case of AA'BB' spectra, as in the 4,4'-dihalobiphenyls, the analyses do not distinguish between and vw or between JAv and Jbb'. In these cases the assignment followed the choice which best agreed with the additivity prediction. The quality of the spectral fitting is indicated by the low root-mean-square deviations obtained, on the average ~0.03 Hz, between calculated and observed frequencies. Visual comparisons of observed spectra and theoretical Lorentz-shape patterns indicated that the computed intensities were satisfactory in each case. Results Table I lists the substituent contributions to the chemical shifts and proton-proton coupling constants for biphenyl and the monohaJobenzenes as determined in deuterated benzene. These substituent contributions are simply the appropriate parameter value
H-H Coupling Constants for Dihalobiphenyls",61
3
0.95 (0.94) 1.03 (1.00) 1.01 (0.98) 1.04 (1.05)
‘
2.58 (2.63) 2.10 (2.16) 2.02 (2.01) 1.73 (1.78)
7.79 (7.76) 7.89 (7.80) 7.75 (7.77) 7.81 (7.77)
0.40 (0.32) 0.47 (0,35) 0.45 (0.35) 0.38 (0.34)
7.50 (7.38) 7.52 (7.42) 7.48 (7.39) 7.46 (7.39)
1.75 (1.73) 1.66 (1.62) 1.69 (1.65) 1.64 (1.64)
1.74
(1.74) 1.79
(1.80) 1.72 (1.78) 1.85 (1.85)
X X
3
F Cl
Br I “
8.34 (8.26) 8.06 (8.01) 8.11 (7.97) 7.99 (7.87)
1.23 (1.12) 1.27 (1.18) 1.21
(1.16) 1.22 (1.23)
4
0.43 (0.32) 0.40 (0.35) 0.40 (0.35) 0.40 (0.34)
All values in Hz. 6 Additivity values c Numbering as shown.
are
7.67 (7.76) 7.67 (7.78) 7.62 (7.77) 7.66 (7.77)
given in paren-
thesis.
(47) S. D. Ross, G. J. Kahan, and W. A. Leach, Soc., 74, 4122 (1952). (48) W. C. Lothrop, ibid., 63, 1187 (1941).
J. Amer. Chem.
The Journal of Physical Chemistry, Vol. 75, No. 3, 1971
A. R. Tabplby, Jb.,
424
Table IH:
and J.
H. Goldstein
Chemical Shifts for Dihalobiphenyls“,M
--©^ 4
3
Compd X =
F
,---—Shifts
calculated by
,-Experimental
additivity-—.
(1)
(2)
(3)
-432.81
-411.18
-411.18
(1)
(2)
-422.36
-409.04
(4) —
432.81
(
Cl
-428.28
-429.26
-429.26
—428.28
Br
-423.41
-438.26
-438.26
-423.41
I
-416.09
-450.39
-450.39
-416.09
+ 10.45)
-417.88 (+10.40) -412.42 (+10.99) -405.07 (+11.02)
shifts(3)
-409.04
(+2.14) -426.43
(+2.14) -426.43
(+2.83)
(+2.83) -435.89
-435.89
(+2.37) -448.16
(+2.37) -448.16
(+2.23)
(+2.23)
(4)
-422.36
(+10.45) -417.88 (+10.40) -412.42 (+10.99) -405.07 (+11.02)
X
X
F
-406.43
-418.17
-423.99
-405.80
-425.82
(+0.63)
-414.56
Cl
-424.51
-413.64
-427.10
-443.90
-423.86
-410.73
Br
-433.51
-408.77
-428.56
-452.90
(+0.65) -432.67 (+0.84)
-405.25
I
-445.64
-401.45
-431.10
-465.03
-445.21
-398.30
(+0.43)
-416.05
(+3.61)
(+2.91) (+3.52) (+3.15)
(+7.94) -415.34 (+11.76) -415.19 (+13.37) -417.47 (+13.63)
-420.33
(+5.49) -436.20
(+7.70) -445,59
(+7.31) -458.28
(+6.75)
X X
1
/
\
•(OHO 3
F
-411.18
-413.42
-409.35
4
-413.02
-432.81
(-1.84) Cl
-429.28
-408.89
-412.46
-428.28
-435.13
Br
-438.26
-404.02
-413.92
-423.41
-446.77
I
-450.39
-396.70
-416.46
-416.09
-463.66
(-5.85) (-8.51)
(-13.2*) » All values in Hz at 60 MHz, relative to 1% internal TMS. ” those shifts calculated by additivity. Numbering as shown.
minus the corresponding value in benzene.28 Table II gives the experimental proton-proton coupling constants for the dihalobiphenyls with the numbering schemes as shown. The values given in parentheses were calculated assuming additivity of substituent effects between biphenyl and the monohalobenzenes and as discussed later are only approximate for dihalobiphenyls. Table III shows the experimental shifts and those calculated by additivity as above for dihalobiphenyls. The values in parentheses are the experimental values minus the additivity values. In Table IV are summarized the substituent effects for adding a second ring to the monohalobenzenes. The ring positions are numbered as shown for the various dihalobiThe Journal of Physical Chemistry, Vol. 75, No. S, 1971
6
-410.54
-415.46
(-2.04) -412.15
(-3.26)
-407.18
(-3.16)
-397.12
(-0.42)
The values given in parentheses
are
(-1.19) -414.43
(-1.97) -416.81
(-2.89) -419.02
(-2.56)
-428.96
(+3.85) -420.33
(+7.95) -418.57
(+4.84) -415.06
(+1.03)
the experimental shifts minus
H-F coupling parameters are given in Table V for difluorobiphenyls analyzed in various solvents. Table VI gives the solvent dependence of biphenyl substituent effects for adding a second ring to benzene. phenyls.
Discussion Previous
nmr
spectral analyses have been reported
(49) J. W. Smith, Bedford College (University of London), private communication. (50) H. R. Snyder, C. Weaver, and C. D. Marshall, J Amer. Chem. Soc., 71, 289 (1949). (51) S. Castellano and A.
A. Bothner-By, J. Chem. Phys., 41, 3863
(1964). (52) R. W. Fessenden and J. S. Waugh, ibid., 31, 966 (1959). (53) C. . Ban well, Mol. Phys., 4, 265 (1961).
Symmetrically Substituted Dihalobiphenyls
425
Table V:
Table IV: Effects on Chemical Shifts of Adding Second Ring for Halobiphenyls0'6
H-F Couplings for Difluorobiphenyls"*’6 Inter-
Solvent
X 3
X
™
H F Cl Br I
Jit
J12
Jn
ring H-F
8.56 8.66 8.39
0.16 0.21 0.21
J14
4,4'-Difluorobiphenyl
4
Ring position(3)
(1)
(2)
”16.80 --7.36 -7.41 -6.82 -6.79
”3.17 ”1.03 -0.34 -0.80 -0.94
-3.17 -1.03 -0.34 -0.80 -0.94
(4)
-16.80 -7.36 -7.41 -6.82 -6.79
5
C6D, CHsCla
CCh
8.56 8.66 8.39
4
5.21 5.36 5.21
5.21 5.36 5.21
3,3 '-Difluorobiphenyl
3,3 '-Dihalobiphenyls
F
,_/
XL-2
F
6
