J. Phys. Chem. 1993,97, 8669-8674
8669
Conformational Studies on Model Compounds of Polyamides with Ether Groups in Their Structure J. de Abajo, J. G , de la Campa, E. Riande,’ and J. M. Garch Instituto de Ciencia y TecnologIa de Pofimeros (CSIC), 28006 Madrid, Spain M. L. Jimeno Centro Nacional de QuImica Orghnica (CSIC), 28006 Madrid, Spain Received: February 3, 1993; In Final Form: May 12, I993
The synthesis of 1,5-dibenzamido-3-oxapentane (DEBA) and 1,8-dibenzamid0-3,6-dioxaoctane (TEBA), model compounds of polyamides with repeating units [-HNCOC~H~CONH(CHZ)ZO(CH~)~-] and [-HNCOC6H4CONH(CH~)~O(CHZ)~O(CHZ)~-], respectively, is reported. The mean-square dipole moment, (p 2 ) , of both compounds was measured in dioxane solutions in the interval of temperatures 30-60 OC. The values of this quantity lie in the ranges 24.6-24.5 DZand 25.4-26.0 DZ,for DEBA and TEBA, respectively. The analysis of the spectral patterns of the model compounds indicates that the energy Ed of gauche states about the C H r C H z bonds adjacent to the amide groups is 0.44f 0.08 kcal mol-’ below that of the alternative trans states. Moreover, semiempirical calculations show that gauche states about NH-CH2 bonds are also preferred over the alternative trans, in contrast with CH2-0 bonds in polyesters, where the opposite occurs. The critical interpretation of the dipole moments of both DEBA and TEBA by the rotational isomeric state (RIS) model suggests that their polarities are very sensitive to the modulus of the dipole moments associated with the amide groups, but they are nearly insensitive to their orientation. Calculations of the dipolar distribution and the corresponding average energies carried out for DEBA and TEBA suggest that the conformers of higher polarity also have the highest energy.
Introduction
CHART I
The conformational dielectric properties of aromatic polyamides with repeating unit -HNCOC6H4CONH(CH2),- have not been widely studied due to the insolubility of these polymers in nonpolar solvents, on the one hand, and to the ability of the amide groups to form intermolecularclusters, on the other hand. The difficulty in measuring dipole moments is reflected by the scattering observed in the values of ( F ~ ) reported ~ / ~ for low molecular weight amide compounds such as N-methylacetamide which range fromlJ 3.68 to 4.22 D. Studies carried out on the orientation of the dipole moments of N,N’-dimethyl amides and their corresponding N-methyl amides indicate that the dipole moment makes an angle /3 = 116 f 4O with the R-C*O
n
0
H
H
0
about C H A H 2 bonds in polyesters containing ether groups in the glycol residue causes the chain to fold back on itself, so that Since the solubility of polyamides can be enhanced by these chains are more coiled than at first sight should be expected. substituting methylene groups by oxygen atoms in the diamine Therefore it is worthwhile to determine the energy of gauche residues, it is important to conduct conformational studies on states about C H A H Zbonds in DEBA and TEBA with respect amides containing ether groups in their structure. As a conseto that of trans states, with the aim to compare it with that quence, this paper deals with the study of the conformational corresponding to similar states about similar bonds in polyesters. characteristics of 1,5-dibenzamido-3-oxapentane(DEBA) and Aside from the much higher polarity of the amide group (-3.7 1 ,8-dibenzamido-3,6-dioxaoctane(TEBA) (Chart I), as a first D) in comparison with that of the ester group (=1.8 D)12, an step to the investigation of the conformational properties of important difference between polyamides and polyesters is that the polyamides with repeating units [-HNCOC6H4whereas O X H 2 bonds show preference for trans states,l&l4 CONH(CH2)z-] and -[-HNCOC~H~CONH(CHZ)ZO(CHZ)~repulsive interactions between the hydrogen atom of the amide O(CH2)2-], of which the low molecular weight compounds can group and the hydrogen atoms of the neighbor phenyl group be considered molecular models. Earlier conformational studieP2 presumably will give rise to preference of gauche states above performed on polyesters obtained by condensation of terephthalic trans about NH-CH2 bonds. Thus the effect of the rotational acid with diethylene glycol and triethylene glycol, respectively, population about these bonds on the polarity of polyamides needs showed some unexpected features. Thus the gauche states about to be investigated. CHz-CHz bonds, which give rise to first-order interactions The goal of this paper is to gain insight into the conformational between oxygen atoms of the ether and ester groups, have an characteristics of polyamides with ether groups in the amine energy significantly lower than that of these states about CHT residue, by the critical interpretation of both the lH NMR spectra CHI bonds in poly(ethy1ene oxide) (PEO) that produce firstand the polarity of the low molecular weight compounds DEBA order interactions between two ether oxygen atoms. The energy and TEBA. The influence of the magnitude and orientation of of these states with respect to that of the alternative trans states the dipole moment associated with the amide group onto the amounts to ca. -0.8 and -0.5 kcal mol-I for the former and latter cases, respe~tively.~J~ The high performance for gauche states polarity of these compounds will be also investigated.
0022-3654/93/2097-8669$04.~0~0 0 1993 American Chemical Society
de Abajo et al.
8670 The Journal of Physical Chemistry, Vol. 97, No. 33, 1993
Experimental Section Chemicals and solvents were reagent grade products, purchased from commercial sources. They were used as received unless otherwise indicated. N,N-Dimethylformamide was vacuum distilled twice over P205. 2,2'-Dichlorodiethyl ether was distilled through a 40-cm Vigreux column. 2,2'-Diphthalimidodiethyl Ether (DPDE). A mixture of 30 g (0.21 mol) of 2,2'-dichlorodiethyl ether, 87 g (0.47 mol) of potassium phthalimide and 300 mL of dimethylformamide was heated to 120 OC (a mild exothermic reaction starts at 50 "C) and maintained at this temperature for 20 h. The cooled reaction mixture was poured into 2.5 L of water. The precipitate was removed by filtration and washed with hot water and ethanol: 59.6 g (80%) of dry DPDE was obtained, mp 156-157 OC (litis mp 156.5 "C). 2,2'-Diaminodiethyl Ether Dihydrochloride (DADE). A mixture of 5 1.O g (0.14 mol) of DPDE, 25.2 mL (0.42 mol) of 85% aqueous hydrazine hydrate solution, and 300 mL of methanol was heated under reflux for 1 h. After cooling, 80 mL of water were added and the methanol was removed under reduced pressure. Concentrated hydrochloric acid (50 mL) and 150 mL of water were heated under reflux for one hour. After cooling to 0 OC, crystalline phthalhydrazine was removed by filtration. The filtrate was concentrated to dryness by evaporation in vacuo. The colored solid was recrystallized twice from absolute ethanol. The yield was 89%; mp 233-234 OC. 1,5-Dibenzamido-3-oxapentane(DEBA). A 6.12-g (19.6mmol) sample of DADE and 3.2 g (80 mmol) of sodium hydroxide were dissolved in 170 mL of water in a 500-mL round-bottoned flask fitted with a fast stirrer. Then 5.62 g (40 mmol) of benzoyl chloride dissolved in 100 mL of dichloroethane were then added to the stirred solution (2000 rpm). After the mixture was stirred for 10 min at room temperature, 100 mL of dichloromethane was added and stirring was stopped. The organic layer was dried over sodium sulfate and the solvent removed under reduced pressure to the point of incipient crystallization. Yield after recrystallization from ethyl acetateln-hexane (120/80 mL) was 85%. Mp: 109-110 OC. Anal. Calcd for C18H20N203 (Mw 312.37): C, 69.21; H, 6.45; N, 8.97. Found: C, 69.29; H, 6.38; N, 9.04. 1,8-Dibenzamido-3,6-dioxaoctane(TEBA). This compound was synthesized from 1,8-diamin0-3,6-dioxaoctane and benzoyl chloride using the same procedure described for DEBA. The yieldwas 92%. Mp: 127-128 OC. Anal. Calcd for CzoH24Nz04 (Mw356.42): C,67.40;H,6.79;N,7.86. Found: 67.47;H,6.68; N, 7.97. NMR Spectra. 'H NMR spectra of DEBA and TEBA were recorded at 30 OC with a Varian XL-300 spectrometer operating at 300 MHz under the following conditions: pulse angle, 77'; acquisition time, 4 s; sweep width, 4000 Hz; data size, 32K. Acetone-ds was used as solvent, and one drop of deuterated water was added to suppress the H-N-C-H couplings. Dielectric Experiments. The dielectric permittivity of solutions of the model compounds (DEBA and TEBA) in dioxane was measured at different temperatures with a capacitance bridge (General Radio, Type 1620 A) operating with a three-terminal cell. The measurements were performed at 10 kHz. Increments of the index of refraction of the solutions with respect to that of the solvent were measured at the temperatures of interest with a differential refractometer (Chromatix, Inc.).
Results (A) NMR Spectra. The lH NMR spectra for the model compounds, represented in Figures l a and 2a, show the region corresponding to the diamine residue. The spectrum of DEBA exhibits a pseudotriplet at 3.646 ppm due to the methylenes linked to oxygen in the N-CH2-CH2-0 sequence and a multiplet centered at 3.554 ppm associated with the methylenes linked to
I
,
3.70
I
,
I
,
3.68 3.66 6. ppm
I
I
I
,
I
358
3.64
I
I
I
I
356 3.54 8 . ppm
I
i
352
Figure 1. Experimental (a) and simulated (b) 'H NMR spectra of the ethylene residues (XCH2-CHzY) corresponding to 1,5-dibenzamido-3oxapentane (DEBA).
h
3.66
I
3.64 3.62 6. ppm
I
I
3.60
I
I
3.58
I
I
I
I
3.56 3.54 6. ppm
I
I
3.52
,
Figure 2. Experimental (a) and simulated (b) 'H NMR spectra of the ethyleneresidues (XCH2-CHzY)correspondingto 1,8-dibenzamido-3,6dioxaoctane (TEBA).
nitrogen in this sequence. The spectrum of TEBA shows a singlet at 3.612 ppm due to the methylenes of the O - C H A H f l fragment, a pseudotriplet at 3.623 ppm due to the methylenes linked to oxygen in the N - C H K H f l sequence,and a multiplet
Model Compounds of Polyamides
The Journal of Physical Chemistry, Vol. 97, No. 33, 1993 8671
TABLE I: Summary of Dielectric Results for 1,5-Dibenzamido-3-oxapenapentane(DEBA) and 1,8-Dibenzamido-3,6-doxaoctane (TEBA) at Several Temperatures ~~
30 40 50 60
0.426 0.432 0.435 0.441
DEBA 9.978 9.549 9.103 8.695
30 40 50 60
0.361 0.367 0.373 0.378
TEBA 9.008 8.641 8.296 8.040
~
24.62 24.60 24.55 24.52
0.830 0.829 0.827 0.826
25.36 25.49 25.62 25.99
0.793 0.798 0.802 0.813
centered at 3.538 ppm corresponding to the methylenes linked to nitrogen in the latter sequence. (B) Experimental Dipole Moments. The dielectric constant E and index of refraction n for each model compound in dioxane solutions were expressed relative to the corresponding values for the pure solvent (el and nl, respectively) in the incremental quantities AE = e - el and An = n - nl. These results were then plotted against the weight fraction of solute w in order to obtain the values of dE/dw and dn/dw in the limit w 0. Values of the two derivatives for both compounds at four temperatures are given in the second and third columns of Table I. Values of the mean-square dipole moment of DEBA and TEBA were then calculated from the standard equation of Guggenheim and Smith16J7
-
where K is the Boltzmann constant, Tis the absolute temperature, M is the molecular weight of the solute, and p is the density of the solvent. Values of (p2) thus obtained are listed in the fourth column of Table I. These results are customarily expressed as the dipole moment ratio, (p2)/nmZ, where nmz is the meansquare dipole moment of the compounds under ideal conditions where the skeletal bonds are freely jointed. In the evaluation of nmz the values of the dipole moments associated with each amide group and with the 0-C bond were assumed to bel4 3.70 and13 1.07 D, respectively. Values of thedipole moment ratio for DEBA and TEBA are given in the fifth column of the Table I; the uncertainty of these results was estimated to be f3%. The temperature coefficient of (p2) for both compounds, expressed in terms of d(ln (pZ)/dT, was obtained by least-squaresanalysis of the experimental results. The values of this quantity amount to -(1.5 0.5) X 1V and (8 f 3) X 1 V K-1, respectively.
*
-1
~ . ~ / . . ~ . , . I . I , ' ' l ~ , ' l . l , l . l l , ~ . l l / . ~
-150
-100
-50
50
0
100
150
4 do) Figure 3. Dependence of the conformational energy on the rotational angles about the CH&H* bonds adjacents to the amide groups. Q' JQ
Trans
Gauche
Figure 4. Conformations of 1,2-disubstitutedethanes according to the Abraham nomenclature.
TABLE Ik NMR S tral Parameters, Chemical Shifts 6 (ppm) and Coupling E a t s J (Hz) Obtained from the Spectra of 1,5-DiberI"ido-3-oxa ntane (DEBA) and 1,8-Dibenzamido-3,6doxaoctaneb B A ) spectral params 6Hl,H2
hi1.m J(H 1 ,H2) J( H 1 ,H3) J(Hl,H4) J(HZ,H3) J(H2,H4) J(H3,H4)
x*
-DEBA
TEBA
3.554 3.810 -15.6 4.4 6.8 6.8 4.4 -1 1.5 0.82
3.551 3.618 -15.6 5.4 6.1 6.1 5.4 -11.8 0.79
Conformational Analysis For the reasons outlined before, an important issue that merits investigation in the conformational analysis of polyamides with ether groups in the diamine residue is the relative energy of the rotamers about CH&Hz bonds. The gauche states about these bonds give rise to first-order interactionsbetween an oxygen atom and a N H group. Semiempirical calculations suggest that the rotational states about these bonds are located at 0, f120°, the energy of the gauche states having an energy ca. 0.7 kcal mol-' below that of the alternative trans states (see Figure 3). The gauche population about CH2-CH2 bonds in the sequence N H C H K H z bonds can also be determined from the critical interpretation of the 1H NMR spectra of Figures 1 and 2. Each of the ethylenegroups of the model compoundscan be considered to be like 1,2-disubstitutedethanes, which have been described extensivelyin the literature.*"" As indicated before, themolecule XCH2CH2Y has three rotational isomers as shown in Figure 4, where the nomenclature of Abraham19 has been used. Superscripts denote the orientationof the coupled protons and subscripts
indicatethe rotamers. The values of thevicinalcoupling constants in the experimental spectrum correspond to average values which are given by
+
+
= n,J; nE*J,8y (3) In order to obtain accurate values for the experimental coupling constants, the spectra were simulated by means of the iterative programz1PANIC 86. The least errors were obtained when the sum of constants J H I , H ~and JHI,H~ were used in the iteration. The values of chemical shifts and coupling constants determined from thesimulationarelistedinTable11. Theethylenespectralpattems of DEBA and TEBA as recorded in acetone-& solution at 30" C, together with thecorresponding simulated spectra, are indicated in Figures 1 and 2. It is clear that the agreement between the experimental and the simulated spectra is excellent. By consideration of ns = nE*, the molar fractions of gauche (X,)and JHI,H4
8672 The Journal of Physical Chemistry, Vol. 97, No. 33, 199'3 35
trans rotamers were obtained by means of the expression
de Abajo et al.
,
30 -
where JH~,HI and J H ~are , Hexperimental ~ constants. As it is imposibletoobtain experimental coupling constants for individual conformers, thevalue of thesequantities wereestimated by means of the Philips and Wray2O equation. This relation permits one to evaluate coupling constants in XCH2CH2Y systems from the dihedral angles and the Huggins substituent electronegativities, the maximum error in the calculations being f 0.27 Hz. The values of x@u& thus obtained for DEBA and TEBA are given in the last row of Table 11. Since the molar fraction of gauche states is related to the conformational energy of these states by the familiar relationship
1
e N
A-
d
20 I -1,5
I -1
-0,5
0 0,5 E (r, (KcaVmol)
1
1,5
Figure 5. Variation of the mean-squaredipole moments with the energy Ed for DEBA and TEBA.
dipole moment associated with the amide groups forms an angle the energy of gauche states with respect to the alternative trans @ of 116 f 4O with the Car-CO bond. The skeletal bond angles (Ed = E p - Et) is found to be -(0.44 f 0.08) kcal mol-'. This were assumed to be 1 loo with the exception of the Car-CO-NH, value is similar to that found for gauche states about CH2-CH2 CO-NH-CH2, and N H - C H r C H 2 bond angles that were bonds in poly(ethy1eneoxide) 13,which cause first-order interaction considered tobe14 114,123,and 112O. GauchestatesaboutNHbetween two oxygen atoms, but is significantly lower than the CH2, CH2-0, and CH2-CH2 bonds were considered to be located energy of gauche states about CH2-CH2 bonds (-0.8 kcal mol-') at i 95O, i looo, and f 120°, respectively, and a t Oo the arising from first-order interactions between two oxygen atoms corresponding trans states were observed. of ether and ester groups, re~pectively.~ Evaluation of the dipole moments of the model compounds The conformational characteristics of the model compounds was carried out at 30 O C by using standard matrix multiplication were also studied by critically interpreting their polarity. The methods, described in detail el~ewhere.1~In the all trans planar conformation of the amide group is by overwhelming conformation, the dipoles associated with the ether and amide difference in energy the preferred structure, and therefore, the groups in DEBA are in nearly parallel direction so that the value OC-NH bond is considered to be restricted to the trans ~ t a t e . ~ ~ , ~of ' p2 for this compound in this conformation amounts to ca. 74 An important difference between esters and amides with ether D2. On the contrary the dipoles are in a nearly antiparallel groups in their structure is that whereas gauche states about direction for TEBA in the all trans conformation and, conseO-CH2 bonds in polyesters are disfavored by11J2J4ca. 0.4 kcal quently, thevalueofp2for thisconformation isca. zero. Departure mol-' with respect to the alternative trans states, the situation is from the trans conformation will, respectively, decrease and somewhat different for gauche states about NH-CH2 in polyincrease the polarity of DEBA and TEBA. By utilizing the set amides. Repulsive interactions between the hydrogen atom of of conformational energies discussed before, specifically, Ed = the N-H group and the hydrogen atoms of the benzoyl residue -0.44, E , -0.5, Ed! = 0.90,E,,k = -0.3, Ea 0.5 and E,,,# are relieved by allowing the rotational angle about the Car-CO 1.4 kcal mol-', one finds that the values of (/r2) at 30 OC for the bond to deviate from zero. Energy calculations were carried out former and latter model compounds are, respectively, 24.0 and by molecular mechanics by using the program PC-MODEL24 25.9 D2, in very good agreement with the experimental results, version 4.0 and by semiempirical methods by utilizing the original 24.6 and 25.4 D2, respectively. The dipole moments of both model parameters of the program A M 125 included in MOPAC,26version compounds are moderately sensitive to the population of gauche 6. The calculated results indicate that gauche states about NHstates about the CHflHz bonds adjacent to the amide group. CH2 bonds are located at f95O, nearly 9O below the rotational The dependence of ( p 2 ) on Ed is shown in Figure 5 where it can angles commonly admitted for these states about C H f l bonds be seen that the dipole moments of both compounds increase as in polyesters. Moreover the energy Eok of those states is nearly Ed increases. Thus the values of ( p 2 )for DEBA and TEBA rise 0.3 kcal mol-' lower than that of the alternative trans states. As from 21.1 and 21.9 D2, respectively, to 32.2 and 32.6 D*, for the energy associated with the conformational status about respectively, when Ed increases from -1.2 to + 1.2 kcal mol-'. the ether 0-CH2 bonds, earlier work carried out on polyethers For the same changes taking place in Erik, the value of ( p 2 ) for indicates that gauche states have an energy,13J4 Ed., 0.9 kcal TEBA increases from 23.6 to 32.5 D2 whereas the value of this mol-' above that of the corresponding trans states. The gauche quantity in the same interval of energy for DEBA slightly decreases state about the central CHz-CH2 bonds in TEBA that produce from 24.8 to 23.3 D2. Considering the uncertainties involved in first-order interactions between two oxygen atoms, as in polythe experimental determination of the dipole moments of the (ethylene oxide), have an energy, E,, 0.5 kcal mol-' below that model compounds, this analysis permits one to conclude that of the alternative trans states.l3 Finally, gauche states of different values of Ed = -(0.3 f 0.2) and Eok = -(0.3 f 0.3) kcal mol-' signs about two consecutive bonds that cause second-order give a good account of the experimental results. The value of Ed interactions C H y O and 0.-NH have energies E,,,and E,., 0.5 thus obtained is somewhat higher than that obtained (-0.44 f and 1.4 kcal mol-' above that of the corresponding tt states. 0.08) kcal mol-' from the critical interpretation of the N M R spectra of DEBA and TEBA. Theoretical Dipole Moments The dependence of ( p 2 ) on the other conformational energies is in comparison rather small. The relatively low sensitivity of The dipole moment associated with the benzamide residue was the dipole moment of these compounds to the conformational taken to be 3.7 f 0.2 D, the average value of the results reported energies may be explained by considering that the dominant for the dipole moment of N-methylacetamide.lJ4 A detailed analysis of the dipole moments of several model amide compounds contributions to ( p 2 ) come from the dipole moments associated carried out by Rodrigo et al.' permit one to conclude that the with the amide groups. Since dipolar interactions decrease fairly
Model Compounds of Polyamides quickly as the number of bonds separating the dipoles increases, the values of (p2) approach those correspondingto freely jointed chains. As a consequence, and as can be seen in Table I, these compounds exhibit intramolecular correlation coefficients (g = (p2)/nm2)close to unity as would be expected for freely jointed chains. This reasoning permits one to predict that the dipole moments of the compounds studied in this work will be only slightly sensitive to the orientation of the dipole moments associated with the amide groups. Actually, in increasing# from I 110 to 120°, the value of ( p 2 ) for DEBA only changes from 23.4 to 24.3 D2, respectively; this change is also only from 26.3 to 25.7 D2for TEBA. The polarity of the compounds, however, is sensitive to the magnitude of the dipoles of these groups. Thus, if this magnitude is assumed to change from 3.7 to 4.2 D, the values of ( p 2 ) for DEBA and TEBA increase, respectively, from 24.0 to 3 1.1 D2 and from 25.9 to 32.9 D*. Therefore, according to this study, a modulus of 3.7 D for the dipole moment associated with the amide group gives a very good account of the experimental results for both compounds. By using the main set of conformational energies indicated above, the values of the temperature coefficient of the dipole moments of TEBA and DEBA are found to be 7.5 X 1 V and 2.3 X 10-4 K-1, respectively. Whereas the value of this quantity for TEBA is in excellent agreement with the experimental result, this is not the case for the temperature coefficient of the dipole moments of DEBA whose experimental value is negative (-1.5 X 10-4). It should be pointed out, however, that small errors of a few tenths in the experimental determination of (p2) can give rise to significant changes in the temperature coefficient, and thereforethis quantity is not so reliable as ( p 2 ) for conformational analysis. Histograms for the distribution, p ( p ) , of the dipole moments of the compounds were obtained by generating all the conformations available and further computing the value of p and the statisticalweight for each conformation. The total conformational partition function, Z,was then obtained by addition of the statistical weights corresponding to all conformations. Moreover, the sum of the statistical weights, z,for the conformations with values of p lying in the interval p f 0.25 was obtained and the value of p ( p ) was determined by normalizing the partial conformationalpartition functions,z,with respect to Z. Values of the average energy corresponding to these conformationswere obtained by summing the statistical weight times the value of the energy of each conformationand then normalizing it with respect to Z. These histograms, together with the average conformational energies, are shown in Figures 6 and 7, respectively. The figures show that TEBA exhibits a more regular distributionthan DEBA. The conformationsfor the latter compound with dipole moments 6.25 f 0.25 amount to ca. 25%of the total. As far as the energy associated with the conformations in the different intervals is concerned, an important difference between both compounds is that whereas conformations with the lowest polarity have energies below (E),in DEBA, these energies are well above (E ) , in TEBA. As a consequence, gauche and trans states about CHTCH2 and C H r O bonds, respectively, must be involved in a predominantly manner in the conformationsof DEBA with lowest polarity. For both compounds, however, the conformations of higher polarity ( p > 7 D) have also energies above (E)t indicating that states of high energy, presumably gauche states about CH-O bonds coupled with rotations of different signs about the pair of bonds NHCHz-CH2 and CH2-CH2 bonds, intervene in these conformtions. As an example, the values of E and r for the g-g+ttg-tg+g-g+ and g+tg+gg+g-conformations of TEBA and DEBA are 5.72 kcal mol-' and 9.64 D for the former conformation and 4.0 kcal mol-' and 8.5 D, for the latter. Though the energy for the other conformations does not follow a definite trend, it is close to ( E ) t .
The Journal of Physical Chemistry, Vol. 97, No. 33, 1993 8673
0
1
I
I
I
I
I
I
I
I
rl
0.2
p . (D)
Figure 6. Distribution of dipole moments (a) and internal energy (b) as a function of the polarity for DEBA (the broken line corresponds to the average energy of all the conformers).
1
3.5
--
-
0.1
a
r-r
a
0.05 0
1 dI
i
'llL1
0.25 1.25 2.25 3.25 4.k5 5125 6.25 7.25 8.25 9.25 p . (D)
Figure 7. Dipolar distribution of the molecular conformersin TEBA (a) and average energies of the conformers (b). (The broken line has the same meaning as in Figure 5.)
Conclusions Two new diamide compounds with enhanced solubility caused by the presence of ether groups in their structure are described. The analysis of the spectral pattern corresponding to the diamine residue permits to conclude that the gauche population about the C H A H 2 bonds adjacent to the amide groups is similar to that reported about C H A H 2 bonds in poly(ethy1ene oxide). This population is, however, significantlylower than that found about C H A H 2 bonds in polyesters in which first-order interactions between an oxygen atom of an ether group and an oxygen atom
de Abajo et al.
8674 The Journal of Physical Chemistry, Vol. 97, No. 33, 1993 of an ester group occur. The critical interpretation of the dipole moments of both compounds indicate that the dipoles associated with the amide groups dominate their dielectric behavior. Moreover, since dipolar interactions die away fairly quickly with distance, the polarity of DEBA and TEBA is very sensitive to the modulus of the dipoles associated with the amide groups but it is nearly insensitive to their orientation. Therefore the value of ( p 2 ) for a polyamide with structural unit -HNCOCsH&ONH(CH2)xshould approach that of a freely jointed chain whenever x 1 4. The rotational isomeric state model gives a very good account of the polarity exhibited by these compounds.
References and Notes (1) McClellan, A. L. Tables of Experimenial Dipole Moments, Rahara Enterprises: El Cerrito, CA, 1974; Vol. 11. (2) Rodrigo, M. M.; Tarazona, M. P.; Saiz, E. J. Phys. Chem. 1986,90, 2236. (3) Shipman, L. L.; Christoffersen, R. E. J. Am. Chem. SOC.1973,95, 1408. (4) Khanarian, G.;Msek, P.; Moore, W. J. Biopolymers 1981,95,1408. ( 5 ) Ldpez Pifieiro, A,; Saiz, E. h t . J . Eiol. Macromol. 1983, 5, 37. (6) Yan, J. F.; Momany, F. A,;Hoffmann, R.;Scheeraga, H. A. J. Phys. Chem. 1970, 74,420. ( 7 ) Rodrigo, M. M.; Tarazona, M. P.; Saiz, E. J . Phys. Chem. 1986,90, 5565.
(8) Iwabuchi, S.;Nakahira, T.; Tsuchiya, A.; Kojima, K. Makromol. Chem. 1982,183, 1427. (9) San R o m h , J.; Guunh, J.; Riande, E.; Santoro, J.; R i a , M. Macromolecules 1982, 15, 609. (10) Riande, E.; GuzmPm, J.; Llorente, M. Macromolecules 1982, 15, 298. (11) Riande, E.; Guzmh, J.; Tarazona, M. P.; Saiz, E. J. Polym. Sci.; Polym. Phys. Ed. 1984,22, 917. (12) Riande, E.; Guzmh, J., J . Polym. Sci.; Polym. Phys. Ed. 1985,23, 1235. (13) Abe, A.; Mark, J. E. J. Am. Chem. SOC.1976,98, 6468. (14) Flory, P. J. Statistical Mechanics of Chain Molecules; Wiley-Interscience: New York, 1969. (15) Dietrich, B.; Lehn, J. M.; Sauvage, J. P.; Blauzat, J. Tetrahderon 1973, 29, 1629. (16) Guggenheim, E. A. Trans. Faraday SOC.1949, 45, 714. (17) Smith, J. W. Trans. Faraday Soc. 1950,46, 394. (18) Gutowsky, H. S.;Belford, G. G.; Mc Mahon, P. E. J . Chem. Phys. 1962, 36, 3353. (19) Abraham, R. J.; Gatti, G. J. Chem. SOC.E 1969, 961. (20) Phillips, L.; Wray, V. J. Chem. Soc., Perkin Trans. 2 1972, 536. (21) PANIC 86, Bruker Program Library. (22) La Planche, L. A.; Rogers, T. J. Am. Chem. Soc. 1964, 86, 337. (23) Hummel, J. P.; Flory, P. J. Macromolecules 1980, 13, 479. (24) PC Model, Serena Software, Blomington, IN. (25) Dewar, M. J. S.;Zocbisch, E. J.; Healy, E. F.; Stewart, J. J. P. J . Am. Chem. Soc. 1985,107, 3902. (26) MOPAC 6.0, Quant. Chem. Progr. Exch. 1990.
ADDITIONS AND CORRECTIONS 1992, Volume 96
1993, Volume 97
David W. Minsek, Joel A. Blush, and Peter Chen*: 1 + 1 Resonant Multiphoton Ionization Spectrum of the Allyl Radical. Rotational Structure in the C[22Bl] %[12A2] Origin Band.
Daniel W. Kohn, Eric S. J. Robles, Cameron F. Logan, and Peter Chen': Photoelectron Spectrum, Ionization Potential, and Heat of Formation of CC12.
Page 2025. Due to an error in the production process, the arrow in the title was printed pointing in the wrong direction. The arrow is correctly displayed in the above title.
Page 4938. Due to an error in the production process, the superscripts and subscripts in Table I wereinadvertently switched. The correct band designations are shown below.
-
-
TABLE I: Some Franck-Condon Factors for CCl$+ CCll Computed by Using the Cartesian Displacement, Internal Coordinate, and Parallel Mode Methods of Handling the Duschinskv Rotation band designation
Cartesian displacement method
internal coordinate method
parallel mode method
1
1 7.0 26 69 8.4 33 82 0.01 1 57 203 214 2927 15598
1 8.0 32 87 3.4 6.0 7.0 0.029 28 109 48 424 3469
5.8
17 35 9.2 43 130 0.030 52 150 232 21991 3487
