2325
Communications to the Editor
TABLE I: Spin Hamiltonian Parameters of AgM (M = Zn, Cd, Hg) AgM
g,,“
AgZn
2.0025
1.9905
AgCd
2.0014
1.9711
AgHg
1.9958
1.9136
a Accuracy *0.0002. legHg.
A,,(= A,) ,b
A,,’,
GHz
GHz
GHz
2.18 (k0.25) 3.13 (iO.20)
1.99 (i0.03) 2.52 (h0.03)
gla
b
Alp,
c
1.324
( i o .003) 1.327 (h0.003) 1.562 (,t0.003)
Coupling
to
C
Coupling
to
1 W d
or
tively. The assignments of the parallel and perpendicular components for the case of AgZn are indicated in Figure 1. The major pattern of the AgCd spectrum is quite similar to that of AgZn, although one of the high-field perpendicular components is masked by the strong Ag signals. A closer inspection of the AgCd spectrum revealed, however, the presence of four groups of satellites (see Figure 2). They were recognized as the perpendicular components of the spectra due to AgCd possessing lllCd (natural abundance = 13%, I = lh, p = -0.5922 PN) or lI3Cd (natural abundance = 1296, Z = l/2, p = -0.6195 PN) nucleus. The corresponding parallel components of these species were too weak to be observed. The major pattern of the spectrum assigned to AgHg is also similar to that of AgZn. In this case, however, the satellite signals attributable to the perpendicular components of AgHg possessing lg9Hg (natural abundance = 17%, I = l/z, p = 0.4993 ON) or 2olHg (natural abundance = 13%,I = %, p = -0.607 PN) were observed providing a further support to the assignment. In each case of AgM discussed above, the large hyperfine coupling interactions with the magnetic nuclei prevented the accurate evaluation of the spin hamiltonian parameters using the usual second-order solutions. The g and the hyperfine coupling tensors of the AgM were, therefore, determined from the observed signal positions resorting to the exact diagonalization of the hamiltonian (1).Table I shows the results. The All% of the magnetic Cd and Hg nuclei were evaluated from the observed perpendicular components of the relevant species. This is possible because, when the magnetic field is perpendicular to the symmetry axis, the off-diagonal elements of the hamiltonian (1) are related to A 1 ’ + A 1’and A 11’ - A 1’.5 The large uncertainties indicated for the A 11”s are due to this indirect approach. In spite of the different separations of the parallel and the perpendicular components, the coupling tensor to the Ag nucleus was found to be completely isotropic (All = A1 = Aiso) in each case. The coupling tensors to the lllCd and lg9Hg nuclei are also essentially isotropic. For Ag atoms isolated in an argon matrix the coupling constant to 107Ag has been measured to be 1.806 GHz4 Using the Goudsmit’s relation6 and the known coupling constants of Ag and Au atoms,4 the isotropic coupling constants of unpaired electrons localized, respectively, in the valence s orbitals of l W d and lg9Hg are estimated to be 12.5 and 40.0 GHz. In the present series of AgM the unpaired electron should occupy the orbital given essentially by an antibonding combination of the valence s orbitals of Ag and M. The ionization potentials of these orbitals are 7.6, 9.4, 9.0, and 10.4 eV for
Ag, Zn, Cd, and Hg atoms, respectively. The dominance of the Ag 5s orbital in the semifilled, antibonding orbital of the present series of AgM is thus expected. The small but clearly observed anisotropies of the coupling tensors to the lllCd and lg9Hg nuclei indicate admixture of the valence pz orbital of the atom M, however. Such admixture would also account for the observed anisotropies of the g tensors with the increasing trend of AgZn < AgCd < AgHg. We have also succeeded in generating and observing the ESR spectra of Ag-alkaline earth intermetallic molecules. The results obtained from these species together with more detailed accounts of the AgM spectra communicated here will be reported soon. References and Notes (1) F. A. Cotton, Acc. Chem. Res., 2 , 240 (1969). (2) K . A. Gingerich, J. Cryst. Growth, 9, 31 (1971). (3) P. H. Kasai, E. 6.Whipple, and W . Weltner, Jr., J. Chem. fhys., 44, 2581 (1966). (4) P. H. Kasai and D. McLeod, J r . , J. Chem. fhys., 5 5 , 1566 (1971). (5) See, for example, ref 4. (6) S . Goudsmit, Phys. Rev., 43, 636 (1933).
Union Carbide Corporation Tarrytown Technical Center Tarrytown, N e w York 1059 1
Paul H. Kasal. D. McLeod, Jr.
Received July 2 1, 1975
Intra- and Intermolecular Hydrogen Bonding in Chlorinated Phenols and Related Compounds Publication costs assisted by the U.S.Environmental Protection Agency
Sir: Paramagnetic relaxation reagents such as trisacetylacetonatochromium [Cr(acac)3] are good proton acceptors, hydrogen bonding to molecules with both strongly and weakly acidic hydrogens.lq2 We wish to show that the combination of intermolecular 13C TI’S (Tie in solutions containing paramagnetic reagents) along with T1 measurements in diamagnetic solutions (intramolecular 13C-lH dipolar TI’S) gives a significant increase of information in studies of solution dynamics for liquids where hydrogen bonding occurs. This is the first report to our knowledge of the use of both techniques to probe chemical dynamics. The I3C TI’Sfor the diamagnetic solution of 3,5-dichlorophenol (solution 1 in Table I) monitor the presence of intermolecular hydrogen bonding in this phenol. The Ti's are half as long as those of the other two dichlorophenols (solutions 2 and 3). Formation of hydrogen bonded molecular aggregates causes the averaged molecular correlation time ( T ~ to ) be approximately twice as long and thus the Tl’s are shortened. For 2,5- and 2,6-dichlorophenol the data indicate less extensive aggregation in solution. This may be explained by a combination of intramolecular hydrogen bonding between the phenolic OH and ortho chlorine atoms and by steric inhibition of intermolecular hydrogen bonding. Interestingly the molecular motion as probed by 13C T1 data is not indicated by the solution macroscopic viscosities (Table I). The 13C Tl’s for 2,5-dichlorophenol are somewhat shorter than those of the 2,6-disubstituted phenol. If one asThe Journalof Physical Chemistry, Voi. 79, No. 21, 1975
Communications to the Editor
2326
TABLE I: Variation in Rate with Copper, HSCHzCOO- , and OH- Concentrations and Temperaturea 105kK, 1 0 4 [ ~ e - 103
105
k’, (CN)$-] [RSH’] [OH-] [Cu2+] T , “C sec-’ 2 .o 2 .o 2 .o 2 .o 2 .o 2 .o 2 .o 2 .o 2.o 2 .o 2 .o 2 .o 2 .o 2 .o 2 .o 4 .O 6 .O 8.O 10.0 12.0 14.0 16 .O 18.0 20 .o 4 .O 20.0
102
M-‘
sec-’
-,.
n
, . e
n
C
“A
c
-1
n
” 1
I
3 .O 0.78 IU z.uu 2.30 1.53 20 4.44 2.90 3 .O 2.03 3 .O 1U 3.3U I .‘I 1 2.53 3 .O 6.46 20 2.55 2.03 30 2.60 3 .O 0.78 30 2.95 3 .O 1.53 4.51 5.45 30 2.68 2.03 3 .O 6.35 30 2.51 2.53 3 .O 2.45 30 1.03 2.38 3 .O 2.61 30 2.53 1.03 3.O 2.69 1.03 30 2.61 3 .O 2.77 2.69 30 1.03 3 .O 2.39 30 2.32 1.03 1.50 1.75 2.43 2.36 30 1.03 2.42 30 2.35 1.03 2.5 2.69 10 1.03 1.5 2.61 2.69 2.61 1.03 10 1.5 2.70 1.03 8 .O 10 2.78 1.5 2.71 2.63 1.03 8 .O 10 1.5 2.80 1.03 2.88 8 .O 1.5 10 1.03 10 2.81 2.73 8 .O 1.5 2.90 1.03 10 2.81 8 .O 1.5 1.03 8 .O 10 2 -94 2.85 1.5 1.03 2.83 2.92 8 .O 10 1.5 2.44 1.03 2.51 8 .O 0 1.5 1.03 2.76 0 2.68 8 .O 1.5 2.0 None added 30 0.082 2.73b 2 .o 20 .o a k ’ is the slope of -In [Fe(CN)e3-] vs. time plots. All concentrations are in moles per liter. bTaking the Cu2f impurity to be 0.03 X 10-5 M , found by analysis of reagent mixtures using diethyldithiocarbamate and extraction with CHC13. 10.0 10.0 10.0 10.0 10.0 10 .o 10.0 10.0 1 .o 2 .o 3 .O 4 .O 2 .o 2 .o 2 .o 8 .O 8 .O
sumes that the (averaged) correlation time for 2,6-dichlorophenol represents largely monomer and T~ for 3,5-dichlorophenol represents an oligomer aggregate, then the mole fraction of dimer may be estimated for the 2,5-dichloropheno1 solution, to be under 25%. This is in agreement with an ir3 and lH4NMR study on ortho-substituted halogenated phenols which showed the existence of “cis-trans dimers” in equilibrium with the monomeric molecules. For o-chlorophenol the molar fraction of the dimer was estimated from cryoscopic measurement to be 10% (0.5 m solution in ben~ene).~ In solutions containing (Cr(acac), the 13C 7’1’s are much shorter than in the diamagnetic solutions; electron-nuclear dipole-dipole interactions dominate the 13C nuclear spinlattice relaxation.2av6With this technique ai. exact evaluation of solvation shell and outer-sphere effects remains elusive because of several complication^.^ Nevertheless, qualitatiue conclusions may be drawn concerning intermolecular hydrogen bonding with Cr(acac)a as well as about other weak solvation effects. When there is intermolecular association between the paramagnetic chelate and phenol molecules due to hydrogen bonding from the OH proton to the ligands of the metal chelate this can be observed in two ways: (1) the phenol 2‘1’s are significantly shorter than T I for the “inert” standard, ccl4; (2) TI for the C-1 and ortho carbons of the phenol (close to the site of complexation) are The Journal of Physical Chemistry, VoI. 79, No. 21, 1975
shorter than the meta and para carbon T I ’ s . ~Several trends can be observed from the data in Table I. In all of the phenols listed in Table I intermolecular hydrogen bonding with the Cr(acac)3 molecules is evidenced. In 3,5-dichlorophenol (solution 4) the C-1 carbon T1 is ca. 20 times shorter than the CCld l3C T I whereas in Dhenol (solution 5) the same ratio is approximately 13. This’difference results from an increase in acidity for the phenolic proton in the dichloro compound. By contrast, the T1 for C-1 in 2,6-dichlorophenol (solution 7 ) is only four times shorter than the CC14 TI. In this case intramolecular hydrogen bonding between the phenolic OH and the ortho chlorines and/or steric effects lessen intermolecular association with the chelate. It is possible to study these effects by doing competition experiments. In solutions 8 and 9, 3,5-dichlorophenol and 2,5-dichlorophenol were run against the unsubstituted phenol. In the 3,5-disubstituted compound the greater acidity of the phenolic OH is indicated by shorter TI’Sfor the C-1 and ortho carbons (by a factor of 2). In the 2,5 compound intramolecular H bonding to the 2-chlorine reverses the competition between the chlorinated and unsubstituted phenols. In an attempt to partially separate the steric and intramolecular hydrogen bonding effects, 2,6-dimethylphenol was used as a steric model for the 2,6-dichlorophenol. Solution 10 contained both compounds. In spite of its greater acidity the 2,6-dichlorophenol shows less tendency to H bond to the Cr(acac)s as evidenced by the longer T I for C-1 and also by the relative lack of polarization of the ring carbon TI’S (comparing the TI’S for all ring positions in both compounds of solution 10). In another exDeriment designed to helr, differentiate between the steric effect and intramolecular hydrogen bond. ing, o-chlorophenol and o -bromophenol solutions containing Cr(acac)a were examined. The bromine substituent is sterically larger and thus steric inhibition of intermolecular H bonding would be more effective than with ortho chlorine atoms. By contrast, bromine is less favorable as an intramolecular H-bond acceptor. To the extent that the model is correct if this intramolecular association is the major cause of reduced intermolecular association then the o-bromophenol TI’Sshould be shorter than those observed for o-chlorophenol.8 This was in fact observed. TI’Sfor C-1 and C-6 in o-bromophenol were ca. 20% shorter than the analogous 2’1’s in a-chlorophenol [C-1: 0.159(Br), 0.185(C1);C-6: 0.139(Br), 0.170(C1); and for the internal “standard,” cresol; C-1, 0.104 sec; C-6,0.074 sec]. We are currently studying these systems in more detail in an attempt to quantify steric and electronic effects and to better determine the nature of the intermolecular interaction between Cr(acac)s and self-associated phenols. I
-
Acknowledgments. We gratefully acknowledge the financial support of the U.S. Environmental Protection Agency and the National Science Foundation. References and Notes ( 1 ) (a) J. P. Fackler, Jr., 1.S. Davis, and I. D. Chawla, Inorg. Chem., 4, 130 (1965): (b) T. S. Davis and J. P. Fackler, Jr., ibid., 5, 242 (1966): (c) M.-F. Rettig and R. S.Drago, J. Am. Chem. SOC.,88, 2966 (1966). (2) (a) G. C. Levy and J. D. Cargioli, J. Magn. Reson., 10, 231 (1973); (b) G. C . Levy and R. A. Komoroski, J. Am. Chem. SOC.,96,678 (1974). (3) (a) I. S.Pereygln and T. F. Akunov, Opt. Spektrosk.. 38, 246 (1972), and literature cited thereln; (b) 0. A. K. Jones and J. G. Watkinson, Chem. Ind. (London), 661 (1961); (c) A. W. Baker and W. W. Kaeollng, J. Am. Chem. SOC.,81, 5904 (1959).
Communications to the Editor
2327
(4) (a) C. M. Huggins, G. C. Pimentel, and J. N. Shoolery, J. Phys. Chem., 60, 1311 (1956); (b) E. A. Allan and L. W. Reeves, ibid., 87, 591 (1963). (5)N. E. Vanderborgh, N. R. Armstrong, and W. D. Spell, J Phys. Chem., 74, 1734 (1970). (6) (a) R. Freeman, K. G. Pachler, and G. N. LaMar, J. Chem. Phys., 55, 4586 (1972); (b) 0. A. Gansow, A. R . Burke, and G. N. LaMar. Chem. Commun., 456 (1972); (c) 8. Barcza and N. Engstrorn, J. Am. Chem. Soc.. 94, 1762 (1972). (7) G. C. Levy, U. Edlund, and J. G. Hexem, J. Magn. Reson., in press. (8) Viewing these effects only as association between the phenols and the Cr(acac)s may be somewhat simpllstic since there is obviously a competition between phenol-phenol and phenol-chelate association. In spite of a significantly greater steric hindrance the carbonyl ligands of Cr(acac)s can compete favorably as hydrogen bond receptors. (9) (a) Alfred P. Sloan Fellow, 1975-1977. (b) On leave of absence from Jagiellonian University, Krakow, Poland. (c) Universitat Dusseldorf, Dusseldorf, West Germany.
George C. Levy"' Tadeusz Holakgb AIOIS steigelgC
Department of Chemistry The Florida State University Tallahassee, Florida 32306 Received March 24, 1975
CloMe6 and C6Me6 in water a t 25O extend to near saturation (1.8 and 2.1 M , respectively, according to Pearson2), and they support the low concentration results of Menger and Wrenn, and also those of Pearson2 obtained from dye uptake and bromide ion activity measurements. Our results for the behavior of 4, with c1/2 for CloMe6 and C6Me6 are shown in Figures 1and 2, respectively. Density measurements for the determination of 4, were made below 0.4 m with 34-cm3 capacity pycnometers to an accuracy of f 4 X g ~ m - and ~ , above this concentration with an automatic precision digital densimeter Model DMA 02C manufactured by Anton Paar KG, the accuracy in this case being f 5 X g ~ m - The ~ . calculated error in 4, at various concentrations is shown by the vertical barred lines on the graphs. The Debye-Huckel theoretical limiting slope (DHLL) is also shown on the graphs. This is given by S, where
s, = kw3/2 in which I
w = 0.5 C u ; z ; ~ and k has a value of 1.868 cm3 for water a t 25°.3 The number of i ions of valence z, formed from dissociation of 1 molecule of electrolyte is given by u,, and thus S , for these compounds is 9.706 cm3 mol-312 L1l2. On the Micellar Properties of Bolaform Electrolytes in Micellization is usually indicated in a &(c1I2) graph by a Aqueous Solution rapid increase in 4, with c~ncentration.~ There is no evidence of this for the C&e6 and C6Me6 bolaforms and so the micellization conditions of Menger and Wrenn are conSir: Last year Menger and Wrennl reported surface tension firmed for n >- 10. However the 4, (c1/2) behavior of our and kinetic measurements on aqueous solutions of bolaU ~ by form electrolytes of general formula R 3 N ( C H 2 ) n N R ~ B r ~ compounds is quite different from that of C ~ B studied Broadwater and Evans.5 This shows a pronounced mini(abbreviated C,&$ R = Me, n-Bu; n = 4, 8, 12). Micellizamum a t about 0.6 M which suggests aggregate formation tion of the C&e6 and C12Bug compounds was inferred above this concentration. The exact concentration a t which from the sigmoidal surface tension vs. log concentration the $,(c~/~) graph for C&u6 deviates from the DHLL was curves for these compounds, and it was suggested that, up not determined by Broadwater and Evans, but, as would be to the highest concentration investigated (0.1 M ) , a miniexpected from the molecular structure, C ~ B Ushows G greatmum chain length of 12 methylene groups was required beer deviations from DHLL than C6Me6 or CloMe6 over the fore micellization occurs for C,Me6 bolaforms. entire concentration range. Our measurements of the apparent molal volumes (4,) of
~
0
0.2
0.4
e-
0.6
,,,ah ib
0.8
1.0
1.2
Figure 1. Variation of apparent molal volume with c"' a t 25' for hexamethonium bromide [ ( C H ~ ) ~ N ( C H ~ ) ~ N ( C H ~ ) ~ . B ~ Z ] . The Journal of Physical Chemistry, Vol. 79, No. 2 7, 1975
