J. Phys. Chem. 1986, 90, 5565-5567 of the CESR line width. It is proposed that these two features result from an increase of the interchain hopping frequency resulting from the bridging of neighboring PMeT chains by isolated Cuz+ ions. The other copper species, most probably clusters of Cu2+ ions, do not modify the transport properties.
5565
Acknowledgment. The technical assistance of D. Simons is gratefully acknowledged. Registry No. PMeT, 84928-92-7; S03CFg-, 3718 1-39-8; Cu2+, 15158-11-9.
Analysis of the Direction of the Dipole Moments of Some Substituted Amides Bearing a Second Polar Group Maria M. Rodrigo, Maria P. Tarazona, and Enrique Saiz* Departamento de Quimica Fisica, Facultad de Ciencias, Universidad de Alcalii de Henares, Alcalii de Henares, Madrid, Spain (Received: January 28, 1986)
The direction of the dipole moment in N-substituted amides has been deduced by analysis of the experimental values of the dipole moments reported in the literature. The compounds studied have a second polar group in addition to the substituted amide group. The results indicate that the dipole moment of the amide group is directed at an angle (3 = 114 2" from the direction of the R-C*O bond, in very good agreement with previously reported results.
*
Introduction The orientation of the dipole moment in the amide group has been studied recently' through analysis of the experimental dipole moments of four N,N'-dimethylamides and their corresponding N-methylamides, following a semiempirical procedure used before2 to determine the orientation of the dipole moment in the ester group. The results obtained were consistent and indicated that the dipole moment makes an angle' /3 = 116 f 4 O with the direction of the R-C*O bond (see Figure 1). The disubstituted diamides previously studied' had one or two degrees of rotational freedom, and therefore, a conformational analysis was required in order to evaluate the average (p2)'l2, whose magnitude was then compared with the experimental results. Moreover, the two polar groups required for the procedure to be applied were both N-substituted amide groups. Thus, it seemed interesting to compare our previous results with the values obtained for other molecules which have only one N-substituted amide group and, besides, have a dipole moment which is independent of the conformation adopted by the molecule. The molecules studied in this paper are p-chloroacetanilide, p-bromoacetanilide, and N-ethyl-p-chlorobenzamide;for all these molecules one of the polar groups is a N-substituted amide group while the second dipole comes from a spherically symmetrical group, namely a halogen atom. The last molecule studied was succinimide, for which its cyclic structure does not allow any rotational freedom, and, therefore, the dipole moment of this molecule does not depend on any conformational parameter. Analysis of Results Table I summarizes the values used in the present work for the dipole moments of the amides studied and those of the model compounds representing their polar groups. All these values, taken from the l i t e r a t ~ r ewere , ~ determined in two different solvents. When more than one result was found for the same molecule, the value shown in Table I and used in this work was the average of the values reported in the same solvent and at the same temperature. p-Bromoacetanilide. Figure 2 shows the structure of this molecule in its planar conformation. Analysis of X-ray diffraction (1) Rodrigo, M. M.; Tarazona, M. P.; Saiz, E. J . Phys. Chem. 1986, 90, 2236. (2) Saiz, E.; Hummel, J. P.; Flory,P. J.; Plavsic, M. J . Phys. Chem. 1981, 85, 3211. (3) McClellan, A. L. Tables of Experimental Dipole Moments, Vol. I; Freeman: San Francisco, 1963. Vol II; Rahara entrp.: El Cerrito, CA, 1974.
0022-3654/86/2090-5565$01.50/0
data has shown4 that the plane containing the amide group makes a dihedral angle of 5.8" with the aromatic ring; however, given the spherical symmetry of the bromide atom providing the second dipole group, the dipole moment of the whole molecule does not depend on the rotation over the C-C*O bond and the conformation used for the present analysis is therefore irrelevant. The dipole moment in benzene solution, shown in Table I, was determined by Smith;s however, the value indicated for p-dioxane solution is the mean of the results reported by Thompson and Hallberg6 ( p = 4.47 D) and Aroney et al.' ( p = 4.66 D). Taking the dipole moment of the p-bromoacetanilide molecule as the vectorial sum of the dipole moment attributable to the Br-phenyl bond pBrc, and that of the amide group pA, one obtains cos
= (pZ- KBrC'
- PA2)/(2pBrCpA)
(1)
where p is the dipole moment of the p-bromoacetanilide molecule and 6 the angle between the dipole moments of the polar groups pBc and pA. Identifying pBrC and pA with the mean of the values reported for the dipole moment of bromobenzene and acetanilide, respectively (seeTable I), and relating 6 to the angle that the dipole moment of the amide group pA makes with the direction of the C-C*O bond /3 (see Figure 2, through the values of the valence angles 0CeNC = 128.9 f 2.3' and OC.CN = 117.7 f 2" obtained from X-ray analysis? we calculated the values of (3 shown in Table 11. p-Chloroacetanilide. The structure of this molecule is similar to that of p-bromoacetanilide (Figure 2). Its dipole moment was measured by Smith5 in benzene solution and by Aroney et al.' ( p = 4.64 D) and Gomel et ale8(k = 4.55 D) in p-dioxane solution for which the value used was, as before, the average between the two results reported in the literature (see Table I). Equation 1 can be used to calculate the value of 6 and, from this, the angle /3 can be obtained from the geometry of the molecule: namely, 6C*NC= 127 f 3" and OCeCN = 114 f 3". Taking the dipole moment of the p-chloroacetanilide molecule as the vectorial sum of the dipole moments attributable to the C1-phenyl bond, identified as the mean of the values reported for chloroben~ene,~ and the dipole moment of the acetanilide3 for the amide group we (4) Andreatti, G. D.; Cavalca, L.; Domiano, P.; Musatti, A. Acta Crystallogr., Sect. B 1968, 24, 1195. (5) Smith, J. W. J . Chem. SOC.1961, 4700. (6) Thompson, H. B.; Hallberg, K. M. J . Phys. Chem. 1963, 67, 2486. (7) Aroney, M. J. Le Fevre, R. J. W.; Singh, A. J . Chem. SOC.1963, 51 1 1 . (8) Gomel, M.; Lumbroso, H.;Peltier, D. C. R. Acad. Sci. 1962,254, 3857. (9) Subramanian, E. Z . Krystallogr. 1966, 123, 222.
0 1986 American Chemical Society
5566 The Journal of Physical Chemistry, Vol. 90, No. 22, 1986
Rodrigo et al.
TABLE I: Dipole Moments Used in This Work
solvent, benzene molecule acetanilide bromobenzene p-bromoacetanilide chlorobenzene p-chloroacetanilide N-ethylbenzamide chlorobenzene N-eth yl-p-chlorobenzamide succinimide acetamide
solvent, p-dioxane
T, OC
0,D
ref
T , OC
0,D
25 25 25 25 25 30 30 30 20 25
3.68' 1.55" 4.36 1.59" 4.32 3.60 1.55" 3.42 1.55 3.65"
3 3 5 3 5 11 3 11 13 3, 15, 16
25 25 25 25 25
3.93" 1.48 4.57" 1.68" 4.60"
3 6 3, 6, 7 3 3, 7, 8
30 30
1.47 3.91'
14 3, 17, 18
ref
"mean values of dipole moments for the same solvent and temperature reported in ref 3 (see text). TABLE 11: Valws of the 0 Angle That the Dipole Moment Makes with the Direction of the R-C* Bond
0,deg molecule p-bromoacetanilide p-chloroacetanilide N-eth yl-p-chlorobenzamide succinimide
solvent, benzene
solvent, p-dioxane
116.8 115.8 109.2 112.3
117.4 115.7 110.8
H Figure 3. Structure of N-ethyl-p-chloroacetanilidein the planar conformation.
0
H' Figure 1. Structure of the amide group showing the angle 0between the dipole moment and the direction of the R-C* bond. Positive direction of the dipole moment is indicated by the arrow.
--D
X
0 ---?
n
h,
py----
H Figure 2. Structure of p-bromoacetanilide shown in the planar conformation.
obtained the values of @ presented in Table 11. N-Ethyl-p-chlorobenzamide. Although we have not found crystallographic data for this molecule in the literature, its structure (represented in Figure 3 in its planar conformation) must be similar to that of N-methylben~amide'~ at least in the features required for the present analysis. The dipole moment of N ethyl-p-chlorobenzamide has been determined by Worsham and Hobbs" in benzene solution at 30 OC (see Table I). The value of fi is given by the following equation: Taking the molecule of chlorobenzene3 as a model compound for the dipole moment of the C1-phenyl bond paB, and the molecule of N-ethylbenzamide" for the amide group M ~ the , value of fl shown in Table I1 was calculated. Succinimide. Figure 4 shows the structure of this molecule for which the crystallographic datal2 indicate that it is planar but (10) Hummel, J. P.; Flory, P. J. Macromolecules 1980, 13. 479. (11) Worsham, J. E.; Hobbs, M. E. J. Am. Chem. Soc. 1954, 76, 206.
0 Figure 4. Structure of succinimide.
presents some asymmetry (i.e., the two valence angles 8CC.N differ by ca. 8') due to the formation of dimers through hydrogen bonding. However, we have treated it as being symmetric since the data of dipole moments that we use were measured in dilute solutions, and under these conditions it is difficult to form intermolecular associations. The valence angles used in this work, 8C*NC*= 110 f 2 O and 8CC" = 115 f 2 O , are averages of the values assigned in the analysis of the crystallogaphic data.12 Thus, if the molecule is assumed to be symmetric, the angle S (see Figure 4) can be obtained as COS
6 = P/(~PAM)
(3)
where p is the dipole moment of succinimide and /.LAM that of acetamide. The dipole moment of succinimide was determined by Cowley and Partingtont3in benzene solution at 20 OC and by Lee and KumlerI4 in dioxane solution at 30 OC. As for the acetamide, its dipole moment in benzene solution at 25 O C was measured by Claeys et al.I5 (pAM= 3.90 0.04D)and Purcell and SingerI6 (/.LAM = 3.38 0.06 D). In p-dioxane solution the
*
*
(12) Sutton, E. L. Tables of Interatomic Distances and Configuration in Molecules and Ions; The Chemical Society: London, 1965; Chem. Soc. Spec. Publ. No. 18. (13) Cowley, E. G.; Partington, J. R. J . Chem. SOC.1936, 47. (14) Lee, C. M.; Kumler, W. D. J . Am. Chem. SOC.1961, 83, 4586. (1 5) Claeys, E. G.; van der Kelen, G. P.; Eeckhaute, Z. Bull. SOC.Chim. Belg. 1961, 70, 462.
J . Phys. Chem. 1986, 90, 5567-5570 reported values a t 30 OC are p A M = 3.90 D (Bats and Hobbs") and P A M = 3.92 D (Kumler18). Using the averages of the values of PAM together with those of p, we calculated the corresponding values of 6 and then, with the above-mentioned valence angles, the resulting 0 shown in Table 11.
Conclusions The average of 6 for the four compounds here studied is 114 f 2O, in good agreement with the value of 116 f 4 O found for the diamides previously studied.l The angle obtained for Nethyl-p-chlorobenzamide is somewhat lower than those of the rest (16) Purcell, W. P.; Singer, J. A. J . Phys. Chem. 1967, 71, 4316. (17) Bates, W. W.; Hobbs, M. E. J. Am. Chem. SOC.1951, 73, 2151. (18) Kumler, W. D. J. Am. Chem. SOC.1952, 74, 261.
5567
of amides. It is noteworthly to point out that Flory et aL2 found a similar difference for para-halogenated benzoate esters whose structure is comparable to N-ethyl-p-chlorobenzamidewith substitution of the ester by amide groups. They concluded that if this difference was real it should be attributed to possible mesomeric effects peculiar to compounds of this kind. The comparison of the values obtained for the angle 6 for N-ethyl-pchlorobenzamide (109.8O) and for N,"-dimethyl-terephthalamide' (120°), in which the chlorine atom has been substituted by a second amide group whose mesomeric effects should roughly compensate those of the first group, seems to corroborate this qualitative idea. Registry No. 4-BrC6H,NHCOCH3,103-88-8; 4-CIC,H,NHCOCH3, 539-03-7; 4-CIC6H4N(CH2CH3)COCH3, 74283-46-8; succinimide, 123-56-8.
Transient Spectroscopy of the Lowest Exclted States of Binuclear Rhodium(I ) I socyanldes Steven J. Milder,* David S. Kliger, Department of Chemistry, University of California, Santa Cruz, California 95064
Leslie G. Butler, Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803
and Harry B. Gray Arthur Amos Noyes Laboratory,t California Institute of Technology, Pasadena, California 91 125 (Received: February 12, 1986)
The binuclear complexes Rh2b(+ (b = 1,3-diisocyanopropane)and Rh2(TMB)2+ (TMB = 2,5-dimethyl-2,5-diisocyanohexane) both exhibit aljsorptionfrom their lowest excited singlet state (lAh) and their lowest triplet state (3Ah). The excited-triplet-state absorption spectra are similar for the two complexes, with strong bands at 420 and 470 nm in Rh2b:+ and at 400 and 490 nm in Rh2(TMB)2+. The two bands are oppositely polarized (x-y, 420 and 400 nm; z, 470 and 490 nm) and are assigned to d r pa (le,, 2alg) and da da* ( l a l g la2,,) transitions, respectively. Both complexes have weak, structureless absorptions in the red (A > 600 nm) that are attributed to pa d6 (2alg d,2-,,2) transitions. The excited singlet spectrum of each complex exhibits a strong band in the blue (450 nm, Rh2b:+; 440 nm, Rh2(TMB)42+)that is primarily z-polarized in Rh2(TMB)42+and is assigned to da* pa (lazu 2al,).
- -
-
-
-
Introduction Excited-state spectra of mononuclear transition-metal complexes have been investigated by several re~earchers-l-~ Binuclear complexes also have received much attenti~n,"~particularly d8-d8 lAZuand species, where the lowest energy transitions are IAl, 3A2,,(d$da*2 d$da*pa).15,1620.21Because these d8-d8 IA,, transitions involve promotion of an electron from da* to a bonding p orbital, the metal-metal bond strengthens and the metal-metal distance contracts in the lowest excited states.'5*20~zz~23 Here we report the excited-state spectra of two binuclear d8-d8 complexes, Rh2b42+ ( b = 1,3-diisocyanopropane) and Rhz(TMB)42+(TMB = 2,5-dimethyl-2,5-diisocyanohexane).We use the ground-state absorption spectra of these complexes and related d7-d7,d7-d8,and ds-dspl species as guides in making assignments.
-
-
-
Experimental Section
Materials. [Rh2b4][BPh4]$4 and [Rh,(TMB),] [CF3S0,]$5 were prepared by published procedures. Propionitrile and isopentane were Aldrich reagent grade and acetonitrile was Burdick and Jackson spectrograde. 2-Methyltetrahydrofuran (2MeTHF) and 2-propanol were Aldrich reagent grade and were distilled +ContributionNo. 7352 from the California Institute of Technology.
0022-3654/86/2090-5567$01.50/0
-
- -
before use. All solvents were dried with 4A molecular sieves. Solutions of the rhodium complexes were prepared for study at (1) Bensasson, R.; Salet, C.; Balzani, V. J. Am. Chem. Soc. 1976,98, 3722. (2) Pyke, S. C.; Ogasawara, M.; Kevan, L.; Endicott, J. F. J . Phys. Chem. 1978, 82, 302. (3) Maestri, M.; Bolletta, F.; Moggi, L.; Balzani, V.; Henry, M. S.; Hoffman, M. Z . J. Am. Chem. SOC.1978, 100, 2694. (4) Viaene, L.; D'Olieslager, A.; Ceulemans, A.; Vanquickenborne, L. G. J. Am. Chem. SOC.1979, 101, 1405. (5) Serpone, N.; Jamieson, M. A,; Henry, M. S.; M. Z. Hoffman, M. Z.; Bolletta, F.; Maestri, M. J . Am. Chem. SOC.1979, 101, 2907. (6) Fleming, R. H.; Geoffroy, G. L.; Gray, H. B.; Gupta, A.; Hammond, G. S.; Kliger, D. S.; Miskowski, V. M. J. Am. Chem. SOC.1976, 98, 48. (7) Miskowski, V. M.; Nobinger, G. L.; Kliger, D. S.; Hammond, G. S.; Lewis, N. S.;Mann, K. R.; Gray, H. B. J . Am. Chem. SOC.1978, 100,488. (8) Miskowski, V. M.; Twarowski, A. J.; Fleming, R. H.; Hammond, G. S.; Kliger, D. S. Inorg. Chem. 1978, 17, 1056. (9) Miskowski, V. M.; Goldbeck, R. A.; Kliger, D. S.; Gray, H. B. Inorg. Chem. 1979, 18, 86. (10) Che, C.-M.; Butler, L. G.; Gray, H. B. J . Am. Chem. SOC.1980,103, 7796. (11) Milder, S.J.; Goldbeck, R. A,; Kliger, D. S.;Gray, H. B. J. Am. Chem. SOC.1980. 102. 6761. (12) Miskowski, V.'M.; Smith, T. P.; Loehr, T. M.; Gray, H. B. J. Am. Chem. SOC.1985, 107, 7925. (13) Levenson, R. A,; Gray, H. B. J . Am. Chem. SOC.1975, 97, 6042.
0 1986 American Chemical Society
