9764
J . Phys. Chem. 1991, 95,9764-9712
Crystallography and AM1 and INDOIS Calculations on Electronic Ground and Excited Singlet States of 2-[p-(Dlmethyiamino)phenyl]-3,3-dimethyl-3H-indole. Solvent Effects on the Absorption and Fluorescence Spectra M. LaCbapelle, M. Belletite, M. Poulin, N. Godbout, F. LeGrand, A. Hiiroux, F. Brisse,* and G . Durocher* DEpartement de Chimie, UniversitP de MontrPal, C.P. 6128, Succ. A , MontrPal. QuEbec, H 3 C 3J7 Canada (Received: April 2, 1991)
Absorption and fluorescence spectra, fluorescence quantum yields (4F), and lifetimes ( T ~ were ) obtained for 2-Lp-dimethylamino)phenyl]-3,3-dimethyl-3H-indole (1) in a series of n-alkanes and n-alcohols, along with the absorption spectrum in the vapor phase. AMPAC and INDO/S calculations as well as crystallographic measurements were also performed on this molecule, using AMPAC for the geometry optimization and INDO/S for electronic transitions calculations and conformational analysis. The structure of 1 was established by single-crystal structure analysis. The refinement converged to a final R value of 0.052 for 1144 observed reflections. The unit cell has dimensions a = 7.978 (4), b = 5.980 (2), c = 16.461 (9)A and fl = 103.09 (4)O,and the space group is nl. It is shown that AMPAC predicts a final geometry similar to that obtained from the crystallographic investigation, while INDO/S calculates transition energies corresponding to those observed in the absorption spectrum of 1 in the vapor phase. It is also shown that INDO/S calculates ground- and excited-state dipole moments similar to those obtained from spectral shift data. The results also indicate that the dimethylanilino ring (PhJ has a certain freedom of rotation in the molecule at room temperature, this motion representing an important deactivation path of the SI excited state. As the viscosity increases in the n-alkane series, the rotation amplitude of the Ph, moiety is reduced, resulting in a decrease of k,, and consequently an increase of $F. The k,, dependence on a fractional power of the viscosity has shown a friction-limited rate for the rotamers inside the energy barrier at room temperature. On the other hand, $F remains constant as the n-alcohol viscosity varies because of a more hindered rotation of the Ph, ring in protic solvents. It is finally shown that the fluorescence spectra are always larger than the absorption spectra in n-alkanes whereas their widths are almost the same in n-alcohols. The ‘bandwidth effect” observed on the spectra in n-alkanes is interpreted in terms of a vibronic interaction taking place between the SI and S2close-lying excited states. On the opposite, such an effect is not observed for 1 in n-alcohols because of the greater stabilization of the more polar SIexcited state. This solvent effect increases the SI-S2energy gap and should therefore weaken the vibronic coupling between them.
Introduction Para-substituted 3H-indole molecules have been studied in our laboratories for a number of years.’4 It has been recognized that the spectroscopic and photophysical properties of these molecules depend on the nature of the e n v i r ~ n m e n t . Recently, ~~ molecule 1 has been used as a fluorescent probe to study the polarity of microenvironments.’*’* It has been suggested on the basis of experimental results that conformational changes occurring during the relaxation of the first excited singlet state are responsible for the photophysical behavior of molecule 1 in nonpolar and polar environments.” Moreover, it was suggested that two close-lying excited singlet states through Herzberg-Teller vibronic coupling are playing an important role in the deactivation of the molecule. A unique decision between these two alternatives cannot be given on an experimental basis alone but has to be looked for by quantumchemical arguments. The aim of this paper is to clarify that situation with the help of crystallography and semiempirical calculations (AMPAC and INDO/S methods) along with a more extensive spectroscopic and photophysical study of molecule 1 in a series of n-alkanes and n-alcohols. In order to obtain further insight into the nature of the electronically excited states governing the photophysics of this molecule, we have used the semiempirical AMPAC and INDO/S methods combined with a CI treatment. The AMPAC method yields reliable results on ground-state geometry and energy values. It is also shown that AMPAC and INDO/S methods are useful tools to obtain a qualitative dynamic picture of the conformational changes of the molecule. This latter image is more accurate than a stiff conformation model, allowing a better understanding of the photophysics of the molecule. Experimental Section 1. Materials. Synthesis and purification of molecule 1 have been done according to methods published by Skrabal et aI.l4
* Authors to whom correspondence
should be addressed.
0022-3654/91/2095-9764%02.50/0
TABLE I: Crystal Data for ~-(Dimethvlamino)~benvl-3,3.-dimethvl-3H-indole CI8NZH2,,,fw = 264.369,monoclinic a = 7.978 (4),6 = 5.980(2).c = 16.461 (9)A 0 = 103.09 (4)*,V = 764.9 A’, pal = 1.148g cm-) Z = 2, P2’,p = 4.86 cm-I, F(000) = 282, T = 20 “C
Ethanol was purified as described elsewhere.’ All the n-alkanes and the other n-alcohols were purchased from Aldrich Chemicals (99+%, anhydrous) and used as received. 2. X-ray Investigation. Single crystals suitable for X-ray diffraction were grown by slow evaporation of a solution of ethanol. The crystal selected was a prism limited by (loo),[OlO),@Ol)whose dimensions were 0.1 1 X 0.18 X 0.38 mm. The crystal was mounted on an Enraf-Nonius CAD-4 diffractometer. The unit cell dimensions were obtained from 25 well-centered reflections in the range 40 < 28 < 50°. Crystal data of interest are given in Table I. The copper radiation, X(Cu Kn) = 1.541 78 A, was ( I ) BelletSte, M.; Scheuer-Lamalle, B.; Baril, L.; Durocher, G. Con. J . Spectrosc. 1977, 22, 31. (2) BelletEte, M.;Durocher, G . Can. J . Specrrosc. 1979, 24, 87. (3) BelletBte, M.; Durocher, G. Can. J . Chem. 1982, 60, 2332. (4) BelletBte, M.; Durocher, G.J. Phofochem. 1983, 21, 251. (5) BelletBte, M.;Lessard, G.; Richer, J.; Durocher, G. J . Lumin. 1986, 34, 279. (6) BelletBte, M.; Lessard, G.; Durocher, G. Con. J. Spectrosc. 1986, 31, A-..Q
(7) Richer, J.; Lessard, G.; BelletZte, M.; Durocher, G. fnf. J . Chem. Kine?. 1986, 18, 1163. (8) BelletZte, M.; Durocher, G. J. Photochem. Phofobiol.,A 1988,44, 275. (9) BelletEte, M.; Lessard, G.; Durocher, G. J. Lumin. 1989, 42, 337. (IO) BelletEte, M.; Durocher, G. J. Colloid InferfaceSci. 1990, 134, 289. ( 1 I ) Belletite, M.; Lachapelle, M.; Durocher, G. J. Phys. Chem. 1990, 94.
7642.
(12) BelletBte, M.; Lachapelle, M.; Durocher, G. J . Phys. Chem. 1990, 94, 5337. (13) BelletZte, M.; Durocher, G. J. Phys. Chem. 1989, 93, 1793. (14) Skrabal, P.; Steiger, J.; Zollinger, H. Helu. Chem. Acta 1975,58,800.
0 I99 1 American Chemical Society
Ground and Excited States of 3H-Indole Derivative graphite monochromatized. The diffracted intensities were collected, at room temperature, in the w mode with a scan width calculated by Au = (1.00 t 0.14 tan e)'. The sphere of reflection was explored up to 28,,, = 140.0' and within the limits given by 0 5 h I9,O Ik I7, -20 5 1 I20. The orientation of the crystal was monitored every 200 measurements while the intensities of the six standard reflections were checked every hour. The largest intensity fluctuation during the measurements of 1808 unique reflections was 1 .I%. A total of 1144 reflections, for which Io 1 1.96u(I), were retained for the structure determination and refinement. The intensities were placed on a common scale and corrected for Lorentz and polarization effects. N o absorption correction was applied since the absorption coefficient was small. The structure was solved by direct methods using the MULTAN 80 set of programs. A full-matrix least-squares refinement of the atomic coordinates and isotropic temperature factors of the semiheavy atoms converged to R = 13.4%. After the temperature factors were converged from isotropic to anisotropic, the refinement converged to R = 10.6%. At this stage a difference Fourier synthesis revealed the positions of all hydrogen atoms. These were included in the refinement process. However, the isotropic temperature factors on the methyl groups were kept at the value of B = 8.0 A. The function minimized was ~ w ( l F o-l IFCI)*. The weights were derived from the counting statistics, w = 1/u2(F). Convergence of the refinement was reached when the maximum and averaged values of the (displacement/sigma) ratio were 0.25 and 0.01, respectively. The residual electron density fluctuations noted on the final difference Fourier synthesis were -0.18 and +0.23 e A-3. The agreement indexes were then R = 0.052, R , = 0.055, and S = 1.648 for 252 parameters.Is The scattering factors for C and N were taken from ref 16 and those for H atoms from ref 17. The programs used here are modified versions of NRC-2, data reduction; NRC-IO,bond distances and angles; NRC-22, mean planes;'* FORDAP, Fourier and Patterson maps (A. Zalkin); MULTANSO, multisolution program;19 NUCLS, least-squares refinement;20 ORTEP, stereodrawings.21 3. Theoretical Calculations. 3.1. Geometry Optimization. We first use the program MODEL on the VAX of the Universite de Montrhl, which enables us to draw the molecule, optimize roughly the geometry using the MM2 force field, and finally generate the corresponding Cartesian coordinates.22 A more precise geometry optimization was obtained using the AM1 (Austin model 1 ) Hamiltonian of the AMPAC program which consists of an improved parametrization for the M N D O Hamilt~nian.~~ 3.2. INDOIS Semiempirical Method. The ground-state and transition energies of molecule 1 have been calculated within the framework of the semiempirical all-valence INDO (intermediate neglect of differential overlap) method including configuration interaction (CI).24*25We used the INDO/S program sent to us by Professor Michael C. Zerner from the University of Florida. The electron-repulsion integrals were evaluated using the Mataga-Nishimoto formula. Within the C I scheme all singly excited configurations involving the 12 highest occupied and the 12 lowest unoccupied orbitals were included. This selection was cut using a threshold for the energy of 60000 cm-' and a threshold for (15) R = ZllF,\- lFcll/XIFI, R , = IZ:w(lF,I - lFc1)'/ZwF,21'/2,and S = [ZW(IF,I - IFJ) / ( m - n)11/*. (16) Cromer, D. T.; Mann, J. R. Acta Crystallogr. 1968, A24, 321. (17) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1%5,
-.
1.-, 2 7175 .-.
(18) Ahmed, F. R.; Hall, S . R.; Pippy, M. E.; Huber, C. P. 1. Appl. Crystallogr.1973, 6. 309. (19) Main, P.; Fiske, S.J.; Hull, S. E.; Lessinger, L.; Germain, G.; Declerq, J. P.; Woolfson, M. M. MULTANBO. A system of computer programs for the automatic solution of crystal structures from X-ray diffraction data. Universities of York, England and Louvain, Belgium, 1980. (20) Doedens, R. J.; Ibers, J. A. Inorg. Chem. 1967, 6, 204. (21) Johnson, C. K . ORTEP, Report ORNL-3794; Oak Ridge National Laboratory: Oak Ridge, TN, 1965. (22) Tai, J. C.; Allinger, N. L. J . Am. Chem. SOC.1988, 110, 2050. (23) Dewar, M. J . S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P. J . Am. Chem. Soc. 1985. 107, 3902. (24) Ridley, J.; Zerner, M. C. Theor. Chim. Acta 1973, 32, I 1 I . (25) Forber, C.; Zerner, M. C. J . Am. Chem. SOC.1985, 107, 5884.
The Journal of Physical Chemistry, Vol. 95, No. 24, 1991 9765
TABLE 11: Fractional Atomic Coordinates and Their Ed's ( X l o ' N and C) and U, (A1, X W ) for the
for
2-[p-(Mmethylamino)pbenyl]-3,fdimetbyl-3~-i~ole Molecule atom x Y z La 1 N(1) 11244 (4) 2989 (6) 2575 (2) 65 ( I ) N(21
c(ij C(3) C(3A) C(4) C(5) C(6) C(7) C(7A) C(8) C(9) C(10) C(l1) C(12) C(13) C(14) C(15) C(16) C(17)
6426 9873 9345 10788 11161 12608 13651 13273 1 I826 8923 9338 8535 7227 6786 7606 9393 7587 6961 5285
(4) i4j (4) (4)
(5) (5) (5) (5) (5) (4)
(5) (5) (4)
(5) (5) (5) (5) (5) (5)
4060 (6) 4178 (7j 5469 (7) 4739 (6) 5291 (7) 4336 (8) 2893 (9) 2341 (8) 3300 (7) 4168 (7) 2617 (7) 2558 (7) 4069 5636 (7) 5644 (7) 8013 (7) 4676 (8) 2571 (8) 5840 (9)
+
-1096 (21 2340 i2j 3048 (2) 3764 (2) 4600 (2) 51 14 (2) 4807 (3) 3958 (3) 3448 (2) 1469 (2) 906 (2) 85 (2) -265 (2) 297 (2) 1124 (2) 2956 (2) 3169 (2) -1667 (2) -1439 (2)
+
72 (11 60 ( i j 60 (1) 59 ( I ) 71 (2) 77 (2) 83 (2) 78 (2) 66 ( I ) 57 ( I ) 67 ( I ) 68 (2) 63 ( I ) 71 (2) 67 ( I ) 77 (2) 74 (2) 83 (2) 89 (2)
+
"Uos = [V,,a*2a2 + U22b*2b2 U33c*2c*2 2U12a*b*ab cos y 2U,,a c*ac cos /3 2Vz3b*c*bc cos a ] / 3 . a, b, c, a,/3, and y are the unit cell dimensions and angles; a*b*, and c* are the reciprocal cell parameters. The U,;s have been deposited, see ref 29.
+
mixing of 200 cm-I. The CI then consists in average of 60 selected single excitations. 4. Instrumentation. 4.1. Absorption and Fluorescence Measurements. The absorption spectra were recorded on a Phillips PU8800 UV/vis spectrophotometer. Corrected fluorescence spectra were measured on a Spex Fluorolog Model 1902. Both types of spectra were then digitized for further manipulations through the use of a Graphpad/IBM-XT system. The fluorescence quantum yield has been measured in n-alkanes by reference to the known value of & = 0.025 for molecule 1 in methylcycloh e ~ a n e .For ~ the measurements in n-alcohols, we use the value for molecule 1 in ethanol (GF= 0.33).13 The theoretical radiative decay rate constant (kk) has been calculated using the Strickler and Berg r e l a t i ~ n . ~ ? ~ ~ 4.2. Liferime Analysis. Fluorescence lifetimes were measured on a time-correlated single-photon counting system, which uses a synchronously pumped cavity dumped, rhodamine 6G dye laser (Coherent CR-599) pumped by a mode-locked argon ion laser (lnnova CR-12) as an excitation source. The laser beam is attenuated by a diaphragm to ensure that the fluorescence count rate is always less than 1% of the cavity-dumper frequency (3.8 MHz). The dye laser beam is frequency doubled by using a KDP 'R6G" crystal (Inrad). Single-fluorescence photons are detected by a photomultiplier tube (Phillips 20204). The signal is conditioned by an Ortec 584 constant fraction discriminator (CFD) whose output serves as the start signal for an Ortec 467 timeto-pulse height converter (TAC). The stop signal comes from a photodiode (Newport Corp., Model 600 A-2), which monitors the output of the dye laser and is conditioned by an Ortec 473A CFD. This signal is delayed (Ortec 425A) such that the signal appears on the screen of a Tracor Northern TN-7200 multichannel analyzer. The 1024-point histogram is accumulated to at least IOOOO counts at its maximum and is transferred to a compatible IBM-XT microcomputer, which is equipped with 640K memory and a 8087 coprocessor.
The lifetimes were obtained by the iterative reconvolution technique (Marquardt algorithm) using the delta function convolution method (DFCM), which gives far better statistical reIn order to judge the quality of the fit, plots of weighted ~ults.~'3~* (26) Strickler, S. J.; Berg, R. A. J. Chem. Phys. 1962, 37, 814. (27) Zuker, M.; Szabo. A. G.; Bramail, L.; Krajcarski, D. T.;Selinger, B. Reo. Scr. Insrrum. 1985, 56, 14. (28) Boens, B.; Amelcot, M.; Yamazaki, I.; De Schryer, F. C. Chem. Phys. 1988, 121, 1 3 .
LaChapelle et al.
9766 The Journal of Physical Chemistry, Vol. 95, No. 24, 1 5191
n
Y
I XJ.
Figure 1. Structure of molecule 1 and atomic numbering.
TABLE 111: Least-Squares Planes in the 3H-Indole Derivative 3H-Indole Plane ( x 3 = 30.9) deviation, 8, deviation, 8,
N(I) C(2) C(3) C(3a) C(4)
0.005 0.009 -0.008 -0.007 0.007
(3) (4) (4) (4) (4)
C(5) C(6) C(7) C(7a)
0.008 0.002 -0.008 -0.009
(4) (4) (5) (5)
C(14)O C(15)"
deviation, 8,
C(8) C(9) C(10) equation
Phenyl Rink ( Y * = 9.1) deviation, A
0.006 (4) -0.000 (4) -0.006 (4) of the phenyl
250
1
/ I
1.240 (4) -1.290 (5)
equation of the 3H-indole plane: 0 . 6 0 8 8 ~+ 0 . 7 7 4 1 ~- 0.17372 = 5.5379 deviation, 8,
Figure 2. Packing of the molecules in their unit cell.
deviation, 8,
C(11) N(2)" 0.024 (3) 0.003 (3) 0.001 (4) C(16)' 0.117 (5) C(12) C(17)' 0.230 (5) C(13) -0.007 (4) ring plane: 0 . 7 4 4 1 ~+ 0 . 6 3 6 9 ~- 0.20182 = 5.9959 Amino Plane
+
equation of the amino plane: 0 . 7 9 0 2 ~ 0 . 5 9 9 1 ~- 0.12962 = 6.1466 Atoms not included in the least-squares plane calculation.
residuals and the autocorrelation function have been examined along with the reduced x2 value and the Durbin-Watson parameter (DW). Our time resolution being 80 ps, some of the shortest lifetimes have been measured in the Center of Fluorescence Spectroscopy of Professor R . Lakowicz, University of Maryland.
Results 1. Crystallographic Investigation. The final positional parameters and their standard deviations are presented in Table Il.29 The atomic numbering is indicated in Figure I . The nine atoms constituting the 3H-indole moiety are coplanar, and so is the phenyl group of atoms. The least-squares planes and the atomic deviations thereof are given in Table IIJ. These two atomic planes are tilted by 11.5' (tilt angle 0) with respect to one another. The two methyl groups at C(3) are nearly symmetrically disposed about the 314-indole plane: C( 14) and C( 15) are at 1.240 (4) and 1.290 ( 5 ) A, respectively, from that plane. In a phenyl ring the C-C distances average 1.379 However, in the phenyl ring of this 3H-indole derivative the C(9)-C( I O ) and C( 12)-C( 13) bond distances are significantly shorter than the other four bonds (Table IV). The corresponding averages are 1.365 and 1.403 A, respectively. Concomitantly, the two endocyclic angles at C(8) and C(l I ) have values of 114.8 and 1 15.5' while the other four ring angles average 122.5O. The sum of the three bond angles around N(2) is 358.8'; thus, the coordination about N(2) is that of a flattened pyramid. Furthermore, N(2) is 0.091 (3) A away from the plane formed by C( 1 I ) , C( 16). and C( 17) and the torsion angles around C(29) The H atom coordinates, anisotropic temperature factors, leastsquares planes, and the table of observed and calculated structure amplitudes have been deposited as supplementary material. (30) Brisse, F.; Sygusch. J . Acta Crysta(logr. 1974, B30, 480.
-
/ /
100~
II
,/
50 1
/
I 45 60 90
0 0
15
75
30
0 (degrees)
Figure 3. Variation of the ground-state energy of molecule 1 as a function of the tilt angle 0 of the Ph, ring by using the INDO/S semiempirical method.
(11)-N(2) deviate from 0 or 180' by up to 10' (Table V ) . As far as the packing of the molecules is concerned, one can observe, in the stereopair in Figure 2, that there is no stacking or overlap. This is most likely due to the presence of the two methyl groups at C(3). The molecules form ribbons extending in the a direction. Within a given ribbon, the molecules are oriented in such a way that their long axis is at 70" from the a direction. 2. Theoretical Study. 2.1. Ground-State Calculations. The AM1 geometry optimization of 1 has been performed, and the results are reported in Tables IV and V . It can be seen that the AMPAC semiempirical method and the crystallography agree reasonably well with each other. Calculations reproduce the experimental values very well. Both techniques emphasize the geometrical distortion within the Ph, ring and in the dimethylamino substituent as well as the tilt angle 0 of the Ph, ring with respect to the indole moiety. Except for one bond in the 3H-indole moiety (C(3A)-C(7A)), all calculated bond lengths agreed quite well with the X-ray structure. The root-mean-square deviation for the bond lengths is 0.010 A. The agreement is also very good for the angles with a difference average of l o . As is well-known though, this agreement stops when one compares the torsional angles (Table V). The disagreement is small for the tilt angle 0 ( 1 1.5' by X-ray and 4.0' by AM1) but more important for the dimethylamino angle with the phenyl ring (6.2' by X-ray and 15.6' by AM1). It is not unusual that the X-ray data, because of the crystal packing involved, leads to smaller dihedral angles. The classical example is the biphenyl molecule which has a planar structure in the crystal, whereas the dihedral angle is -45' in the vapor phase.)' More recent examples have also been given recently on the 3-hydroxyflavone where the X-ray structure analysis has been compared with the AMI c a l ~ u l a t i o n . ~ ~ The INDO/S semiempirical method has been used to calculate the energy of the molecule at various tilt angles 0 of the Ph, ring, (31) Almenningen. A.; Bastiansen, 0.;Fernholt, L.; Cyvin, 9. N.: Cyvin, S. J.; Samdal, S. J . J. Mol. Struct. 1985, 128, 59. (32) Dick, B. J . Phys. Chem. 1990, 94. 5752.
The Journal of Physical Chemistry, Vol. 95, No. 24, 1991 9767
Ground and Excited States of 3H-Indole Derivative
TABLE I V Bond Distances and Angles in 2-[p (Dimetbylamino)pbenyl]-3,3-dimethyl-3H-in~~Obtained from tbe X-ray Structure Determination and by the AMPAC Method4
N(I)-C(2) C(2)-C(3) C(3)-C( 3a) C(3a)-C(4) C(4)-C(5) C(5)-C(6) C(6)-C(7) C(7)-C(7a) C(3a)-C(7a) C(3)-C( 14) C(3)-C( 15)
X-ray 1.288 (5) I .534 (5) 1.513 (5) 1.381 (5) 1.390 (6) 1.372 (6) 1.401 (6) 1.388 (6) 1.376 (5) 1.530 (6) 1.536 (5)
AMPAC 1.323 1.561 1.519 I .379 1.403 1.392 1.401 1.394 1.433 1.515 1.514
C(2)-N( 1)-C(7a) N ( 1 )-C( 2)-C( 3) C(2)-C(3)-C(3a) C(3)-C( 3a)-C(4) C( 3)-C(3a)-C( 7a) C(4)-C(3a)-C(7a) C(3a)-C(4)-C(5) C(4)-C( 5)-C(6) C(5)-C(6)-C(7) C(6)-C(7)-C(7a) C(7)-C(7a)-N( 1 ) C(7)-C(7a)-C(3a) N ( 1)-C(7a)-C(3a) C(2)-C(3)-C( 14) C(Z)-C(3)-C( 15) C(3a)-C(3)-C( 14)
107.0 (3) 114.2 (3) 98.9 (3) 131.4 (3) 107.6 (3) 120.9 (4) 118.1 (4) 121.6 (4) 120.3 (4) 117.9 (4) 126.5 (4) 121.3 (4) 112.2 (3) 114.1 (3) I 1 1.0 (3) 109.4 (3)
108.3 112.9 100.1
131.7 107.4 120.9 118.3 121.0 121.5 117.9 128.4 120.4 1 1 1.3 112.4 1 1 1.9 109.4
C(2)-C(8) C(8)-C(9) C(9)-C(IO) C(I0)-C(I 1) C(ll)-C(I2) C( I2)-C( 13) C(8)-C( 13) C(l I)-N(2) N(2)-C( 16) N(2)-C( 17) N( I)-C(7a)
X-ray 1.462 (5) 1.403 (5) 1.359 (5) 1.402 (5) 1.416 (5) 1.370 (5) 1.391 (5) 1.372 (5) 1.428 (6) 1.432 (6) 1.419 (5)
AMPAC 1.461 1.406 1.387 1.417 1.417 1.388 1.401 1.400 1.437 1.439 1.424
C(3a)-C(3)-C(15) C(14)-C(3)-C(I5) N( 1)-C(2)-C(8) C(3)-C(2)-C(8) C(2)-C( 8)-C( 9) C(2)-C(8)-C( 13) C(9)-C( 8)-C( 13) C(8)-C(9)-C(lO) C(9)-C(IO)-C(I 1) C( 10)-C( 1 1)-C( 12) C( 1 I)-C( 12)-C( 13) C( 12)-C( 13)-C(8) C(l I)-N(2)-C(16) C(1 I)-N(2)C(17) C( 16)-N(2)-C( 17) N(2)-C(1 l)-C(lO) N(2)-C(ll)-C(l2)
111.5 (3) 111.3 (3) 120.6 (3) 125.2 (3) 120.2 (3) 125.0 (3) 114.8 (3) 123.1 (4) 122.1 (4) 115.5 (3) 121.2 (4) 123.4 (4) 121.2 (3) 120.1 (3) 117.5 (3) 122.8 (3) 121.7 (3)
110.2 112.1 122.9 124.2 119.8 122.7 117.5 121.5 121.0 117.3 120.9 121.8 118.5 118.0
117.3 121.8
120.9
Bond distances are in angstroms and angles in degrees. TABLE V Torsional Angles of Interest and Their Estimated Values
C( lO-C( 1 I)-N(2)-C( 16) C(I0)-C(I I)-N(2)-C(17) C(I2)-C(1 I)-N(2)-C(16) C( 12)-C( I I)-N(2)-C( 17)
X-rav -3.7 (5) -170.8 (4) 175.7 (4) 8.6 (5)
AMPAC -5.7 -157.5 177.3 25.5
N( 1)-C(2)-C(8)-C(9) N( I)-C(2)-C@)-C( 13) C(3)-C( 2)-C(8)-C(9) C(3)
