Crystal, Molecular, and Electronic Structure of 1-Acetylindoline and Derivatives

Structural Chemistry, ol. 9, No. 5, 1998 Crystal, Molecular, and Electronic Structure of 1-Acetylindoline and Derivatives M. M. Torres Moreno,1 R. H. A. Santos,2 M. T. P. Gambardella,2 A. J. Camargo,2 A. B. F. da Silva,2,3 and M. Trsic2 Received April 11, 1997; revised April 14, 1998; accepted April 28, 1998 The crystal and molecular structures of the following molecules have been determined: 1-acetylindoline, 1-acetyl-5-nitro-indoline, l-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitroindoline, and l-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species. KEY WORDS: 1-Acetyl-indoline; crystal structure; electronic structure; AM1 calculation; CI calculation. INTRODUCTION The photosolvolisis of nitroderivatives of 1-acetylindoline (see Fig. 1) has been known since 1976 [1, 2]. Nitro derivatives of 1-acetyl-indole undergo the same reaction [3]. The reaction does not take place in the absence of the nitro group in the 7 position [3]. In order to provide a better understanding of these chemical species we have determined X-ray crystal and molecular structures of the following compounds: 1-acetyl-indoline (), l-acetyl-5-nitro-indoline (), l-acetyl-5-nitro-7-bromo-indoline (), l-acetyl-5- bromo-7-nitro-indoline (), and l-acetyl-5-bromo-7- nitro-indol () [4]. The results of the X-ray study are described in the next section. Then we report molecular orbital (MO) calculations for the same compounds, plus the debrominated 1-acetyl-7-nitro-indoline (I) and 1-acetyl-7-nitro-indol (II) species. 1 Departamento de Petrologia, Instituto de Geociencias UNESP, P.O. Box 178, 13560-900, Rio Claro, SP, Brasil. 2 Departamento de Quimica e Fisica Molecular, Instituto de Quimica de Sao Carlos, Universidade de Sao Paulo, P.O. Box 780, 13560-970, Sao Carlos, SP, Brasil. 3Correspondence should be directed to A. B. F. da Silva, Departamento de Quimica de Sao Carlos, Universidade de Sao Paulo, P.O. Box 780, 13560-970, Sao Carlos, SP, Brasil; e-mail: Alberico@iqsc.sc.usp.br Fig. 1. Chemical formulae of the molecules studied by X-ray diffraction. 365 1040-0400981000-0365$15.000 1998 Plenum Publishing Corporation

366 Torres Moreno et al. Crystal and Molecular Structure Determination The crystal structures of compounds I to were obtained from a CAD-4 Enraf-Nonius automatic diffractometer and all structures were solved using direct methods [7]. The refinement was carried out by full-matrix least squares calculations [8] with anisotropic thermal parameters for non-h-atoms and isotropic thermal parameters (6 A 2 ) for H atoms. The crystal data and conditions are shown in Table I. In the refinement of the structures the minimized function was Ew i (k F 0 \ - \F C \) 2 with w i -1 = a 2 (F 0 ) + pf 2 for observed reflections, except in compound, where unit weights were used and w = 0 for nonobserved reflections. The H positions were assumed by the geometries of the bonded atoms and the H coordinates were recalculated after each refinement cycle until the final convergence with maximum least squares shifte.s.d. < 1 was obtained. The final converged values for R and R w and the maximum electron density calculated after the last refinement cycle are shown in Table I. Final atomic parameters for the non-h-atoms are given in Table II. (A list of structure factors, anisotropic thermal parameters, and hydrogen positions are available from the authors on request.) The bond lengths and angles are shown in Tables and. The torsion angles are given in Table. Some important planes and atomic distances to them are indicated in Table I. The bond distances in the benzene ring of compound are the same as in the benzene molecule and the variations observed in the substituted molecules can be attributed to the substituent influence. In compound, the C=O distance has a usual value (1.16(1) A), and in, for the two independent molecules, the intramolecular distance between the carboxyl oxygen and one of the nitro group oxygens is very short (2.7 A), probably due to the reduction of the indolinic ring tensions. Table I. Crystal Data for the Compounds I to Compound formula I C 10 H 11 ON C 10 H 10 N 2 0 3 C 10 H 9 N 2 O 3 Br C 10 H 9 N 2 O 3 Br C 10 H 7 N 2 O 3 Br Formula wt. Space group a (A) b (A) c (A) a ( o ) B ( ) r ( o ) v (A 3 ) z D c (g.cm- 3 ) F(000) u MoKa (cm -1 ) Size (mm.10 2 ) Scan type Range 2o max. ( ) Unique data I > 3e(I) N variables Final R Final Rw Rall S* w** (p. 10 3 ) 161.21 Pbca 9.439(2) 12.046(2) 14.870(4) 1691(1) 8 1.27 688 0.80 10 x 10 x 40 w -2o 0 < h < 10 0 < k < 13 0 < < 16 22.97 1178 870 114 0.0447 0.0517 0.0744 2.17 1.84 206.21 P2 1 c 11.287(2) 12.017(2) 7.425(3) 102.57(2) 983.0(8) 4 1.39 432 0.65 10 x 10 x 30 w -2o -13 < h < 13 0 < k < 14 0 < < 8 24.97 1734 366 71, 70 0.0624 0.3051 1.66 w = 1.0 285.11 P1 7.14 7.91 10.901(2) 72.01(1) 87.02(2) 64.97(2) 528.3(2) 2 1.79 280 37.77 20 x 20 x 30 w -2o -8 < h < 8-8 < k < 9 0 < l < 12 24.97 1858 1524 151 0.0279 0.0300 0.0568 1.95 1.23 285.11 P2 1 c 13.699(2) 9.019(2) 8.724(2) 90.3 1077.9(7) 4 1.76 588 37.08 10 x 20 x 30 w-2e -16 < h < 16 0 < k < 10 0 < < 10 24.98 1888 644 80, 71 0.0498 0.0498 0.2040 2.20 0.78 283.11 P2 1 c 12.066(2) 7.051(1) 24.532(3) 93.14(2) 2083.9(6) 8 1.82 1120 38.55 10 x 10 x 30 u -28-14 < h < 14 0 < k < 8 0 < l < 28 24.98 3634 1463 149, 149 0.0396 0.0396 0.1676 1.45 0.50 *S = [Ew( F 0 - F C ) 2 (N - M)] 12 **w = 1.000[<r 2 (F 0 ) + p(f 0 ) 2 ]

Structure of 1-Acetyl-indoline and Derivatives 367 Table II. Atomic Coordinates and Isotropic-Equivalent Temperature Factors (A 2 ) with e.s.d.'s. for Compounds to Atom Xa Yb Zc B eq Compound I N(l) Compound II 0(3) N(l) Compound Br 0(3) N(l) Compound Br O(l) O(2) O(3) N(1) 0.5528(2) 0.3963(2) 0.4920(3) 0.3209(3) 0.2295(3) 0.1790(3) 0.2160(3) 0.3174(3) 0.3858(3) 0.3468(3) 0.2461(3) 0.5220(3) 0.47-0.138(1) -0.114(1) 0.3826(9) -0.08 0.477(1) 0.386(1) 0.263(1) 0.077(1) 0.043(1) 0.114(1) 0.229(1) 0.269(1) 0.196(1) 0.591(1) 0.0471(1) -0.0204(3) 0.3750(4) 0.4955(4) -0.2206(4) 0.3722(4) -0.1859(5) -0.3686(5) -0.2472(5) 0.0733(5) 0.2162(4) 0.2130(4) 0.0684(4) -0.0668(4) -0.0699(5) -0.3643(7) 1.043 0.5744(5) 0.7578(5) 0.7311(5) 0.6495(5) 0.7549(5) 0.5701(7) 0.6397(6) 0.7246(8) 0.8791(6) -0.0522(2) 0.0725(2) -0.010 0.1262(2) 0.2166(2) 0.2491(2) 0.2189(2) 0.140 0.0861(2) 0.1149(2) 0.1966(2) -0.0459(2) 0.859(1) 0.709(1) 0.887(1) 0.6940(9) 0.789(2) 0.759(2) 0.571(1) 0.535(1) 0.659(1) 0.766(2) 0.858(1) 0.842(1) 0.73 0.642(1) 0.96(1) 0.3734(0) 0.2194(3) -0.4565(4) -0.2405(4) 0.1408(4) -0.3007(4) 0.2181(4) 0.0477(5) -0.1496(5) -0.2412(4) -0.1769(4) 0.0021(4) 0.1195(4) 0.0505(4) -0.1225(4) 0.3032(6) 0.2529(2) 0.0582(8) -0.1346(8) -0.0549(9) 0.2645(9) -0.034(1) 0.167(1) 0.425(1) 0.503(1) 0.383(1) 0.2951(1) 0.2417(1) 0.2307(2) 0.166 0.210 0.3796(2) 0.4669(2) 0.482 0.4115(2) 0.3245(1) 0.3088(1) 0.1358(2) 0.298(2) -0.276(2) -0.227(2) 0.214(1) -0.205(2) 0.295(2) 0.203(2) 0.096(2) -0.068(2) -0.092(2) -0.022(2) 0.076(2) 0.111(2) 0.04 0.383(20) 0.1816(0) -0.0225(2) 0.6187(2) 0.5787(3) 0.1309(2) 0.5556(3) 0.0046(3) 0.1643(3) 0.2679(3) 0.4204(3) 0.4454(3) 0.3725(3) 0.2667(3) 0.2345(3) 0.3153(3) -0.0956(4) 0.0465(1) 0.2775(8) 0.2049(8) 0.4352(9) 0.3641(8) 0.305(1) 0.346(1) 0.403(1) 0.32 0.19 5.47(7) 3.69(6) 4.13(8) 4.62(9) 4.24(8) 4.61(8) 4.91(9) 4.78(9) 4.22(8) 3.63(7) 3.71(1) 5.2(1) 8.9(5) 11.9(8) 12.2(7) 4.6(4) 1 5.7(6) 6.4(6) 6.7(6) 6.0(6) 5.7(6) 5.9(6) 5.3(5) 4.5(5) 5.1(5) 8.0(7) 3.25(2) 3.5(1) 4.9(2) 5.5(2) 2.7(1) 3.6(2) 3.1(2) 3.9(2) 3.5(2) 2.8(2) 2.7(2) 2.6(2) 2.4(2) 2.4(2) 2.7(2) 5.0(3) 4.89(5) 2.1(3) 4.6(3) 4.7(3) 2.9(4) 3.2(4) 3.7(4) 4.8(5) 3.3(4)

368 Torres Moreno et al. Table II. Continued Atom Compound a Br(1) 0(3) N(1) Compound b Br(2) 0(11) 0(21) 0(31) N(11) N(21) C(11) C(21) C(31) C(41) C(51) C(61) C(71) C(81) C(91) C(101) Xa 0.9206(7) 0.8742(7) 0.7891(8) 0.7405(7) 0.7902(8) 0.4801 Yb 0.24 0.111(1) 0.115(2) 0.242(2) 0.379(1) 0.223(1) Zc 0.149(1) 0.181(1) 0.254(1) 0.293(1) 0.266(1) 0.431(1) B eq 3.2(4) 4.0(5) 2.8(5) 3.0(4) 3.1(5) 4.3(5) 0.7965(1) 0.2184(5) 0.3924(5) 0.3361(6) 0.3236(5) 0.3883(5) 0.2182(7) 0.3388(7) 0.4473(7) 0.6186(6) 0.6478(6) 0.5692(6) 0.4601(6) 0.4259(6) 0.5066(6) 0.1172(7) 0.1451(2) 0.167(1) 0.182(1) 0.434(1) 0.2948(9) 0.288(1) 0.248(2) 0.316(1) 0.289(1) 0.223(1) 0.192(1) 0.204(1) 0.242(1) 0.262(1) 0.256(1) 0.319(1) 0.4365(0) 0.4195(3) 0.3280(3) 0.3681(3) 0.4899(3) 0.3671(3) 0.4614(4) 0.5465(4) 0.5611(3) 0.5036(3) 0.4516(3) 0.4070(3) 0.4158(3) 0.4689(3) 0.5130(3) 0.4894(4) 4.06(3) 4.7(3) 5.9(3) 4.9(3) 2.6(3) 3.5(3) 3.8(4) 3.5(4) 2.8(3) 2.8(3) 2.8(3) 2.5(3) 2.1(3) 2.4(3) 4.2(4) 0.5991(1) 1.1328(4) 0.8853(5) 1.0024(5) 1.0951(5) 0.9339(6) 1.1669(7) 1.1249(7) 1.0367(7) 0.8274(7) 0.7545(7) 0.7892(6) 0.9017(7) 0.9790(6) 0.9381(6) 1.2890(6) 0.2671(2) 0.1605(9) 0.24 0.456(1) 0.2971(9) 0.334(1) 0.235(1) 0.303(1) 0.305(1) 0.289(1) 0.282(1) 0.291(1) 0.298(1) 0.294(1) 0.296(1) 0.267(2) 0.2411(0) 0.1382(2) 0.0774(3) 0.1064(2) 0.2192(2) 0.1139(3) 0.1794(4) 0.2759(3) 0.3045(3) 0.2768(3) 0.2303(4) 0.1786(3) 0.1692(3) 0.2143(3) 0.2679(3) 0.1924(4) 4.76(4) 3.4(2) 5.1(3) 4.1(2) 2.4(2) 2.7(3) 3.4(4) 2.7(3) 2.8(3) 2.1(3) 2.4(3) 4.7(4) Table. Bond Lengths (A) with e.s.d's. for the Compounds I to -C(1) N(1)-C(1) N(1)- N(1)- C(1)- - 1.227(3) 1.353(4) 1.481(4) 1.412(3) 1.503(4) 1.536(4) II 1.2 1.35(2) 1.48(2) 1.42(1) 1.51(3) 1.51(2) 1.207(5) 1.380(4) 1.498(6) 1.399(4) 1.495(5) 1.527(5) 1.16(1) 1.41(1) 1.49(1) 1.41(1) 1.53(1) 1.54(1) a 1.18(1) 1.46(2) 1.4 1.383(9) 1.52(1) 1.35(1) b 1.19(2) 1.42(2) 1.42(1) 1.400(9) 1.51(1) 1.31(1)

Structure of 1-Acetyl-indoline and Derivatives 369 Table HI. Continued - - - - - - - O(2)- 0(3)- - - Br- Br- 1.497(3) 1.393(4) 1.382(3) 1.367(4) 1.392(3) 1.390(4) 1.389(3) II 1.5 1.34(2) 1.42(2) 1.4 1.36(2) 1.43(2) 1.37(2) 1.22(3) 1.24(3) 1.48(2) 1.510(6) 1.388(6) 1.373(4) 1.384(4) 1.382(4) 1.397(5) 1.389(4) 1.204(5) 1.232(5) 1.460(4) 1.877(3) 1.51(2) 1.45(1) 1.4 1.36(2) 1.33(1) 1.37(2) 1.44(2) 1.27(1) 1.2 1.49(2) 1.908(9) a 1.43(1) 1.36(1) 1.4 1.42(2) 1.37(2) 1.39(2) 1.42(2) 1.22(1) 1.21(1) 1.47(2) 1.882(8) b 1.45(2) 1.4 1.37(1) 1.36(1) 1.4 1.41(2) 1.43(2) 1.24(1) 1.21(1) 1.45(2) 1.913(8) Table. Intramolecular Bond Angles ( ) with e.s.d's. for the Compounds to C(1)-N(1)- C(1)-N(1)- -N(1)- O(1)-C(1)-N(1) -C(1)- N(1)-C(1)- N(1)-- -- -- -- -- -- N(1)-- N(1)-- -- -- -- -- O(2)--0(3) O(2)-- O(3)-- O(2)-- O(3)-- -- -- -- -- Br-- Br-- Br-- Br-- 123.4(2) 126.3(2) 110.2(2) 121.5(2) 121.8(2) 116.8(3) 104.8(2) 104.2(2) 118.5(2) 120.7(2) 121.7(2) 117.5(2) 129.3(2) 109.7(2) 121.0(3) 128.8(2) 110.5(2) 120.7(3) II 126(1) 127(1) 108(1) 122(1) 123(1) 115(1) 106(1) 105(1) 115(1) 126(1) 119(1) 117(1) 128(2) 112(2) 121(1) 129(1) 109(1) 121(1) 125(2) 117(2) 118(2) 117(1) 117(2) 122.3(3) 123.3(3) 107.3(2) 121.3(3) 122.1(3) 116.7(3) 105.1(3) 102.8(3) 117.1(3) 122.7(3) 119.4(3) 118.6(3) 128.6(3) 111.0(3) 120.3(3) 129.0(3) 109.6(3) 121.4(4) 126.3(3) 118.6(3) 118.1(3) 118.5(3) 118.7(3) 118.4(2) 122.8(2) 124.1(8) 123.1(9) 108.7(9) 123.3(8) 125.3(9) 111.4(8) 105.5(7) 105.1(8) 117(1) 121.7(9) 119(1) 125(1) 131(1) 112(1) 116.7(9) 131(2) 107.7(9) 121(2) 123.6(9) 115.5(8) 120.8(9) 113(2) 122(1) 114.0(7) 124.3(8) a 124.4(7) 123.9(7) 108.5(7) 119.1(8) 126.6(8) 114.2(8) 108.7(7) 109.0(7) 118.8(8) 121.4(8) 120.0(7) 120.1(7) 132.9(7) 108.2(7) 119.0(7) 133.8(7) 105.7(7) 120.5(8) 125.7(8) 117.1(8) 117.1(8) 116.2(7) 123.0(7) 120.8(6) 117.8(6) b 123.8(6) 125.9(6) 106.5(6) 121.8(7) 122.2(9) 115.9(7) 111.0(7) 109.3(7) 116.6(8) 123.1(7) 120.7(7) 118.7(8) 133.2(8) 108.4(6) 118.4(7) 132.7(7) 104.9(7) 122.4(7) 124.8(8) 116.2(2) 119.0(7) 118.3(7) 122.5(7) 117.8(7) 119.2(7)

370 Torres Moreno et al. Table. Selected Torsion Angles ( ) with e.s.d's. for the Compounds to -N(1)-C(1)-O(1) -N(1)-C(1)- -N(1)-C(1)- -N(1)-C(1)- C(1)-N(1)-- -N(1)-- C(1)-N(1)-- C(1)-N(1)-- -N(1)-- -N(1)-- N(1)--- --- --~ --- --- --- --- --- --- --- --- ---N(1) --- N(1)--- N(1)--- ---N(1) --- --- --- O(2)--- O(2)--- O(3)--- O(3)--- O(2)--- O(2)--- O(3)--- O(3)--- Br--- Br--- Br--- Br---N(l) Br--- 179.2(2) 0.8(3) -4.7(4) 176.4(2) -177.8(2) 6.0(3) 2.2(4) -178.2(2) 178.4(2) -2.0(3) -7.3(3) -175.0(3) 6.6(3) 0.7(4) -177.6(3) 0.7(4) -0.9(4) -0.3(4) -178.7(2) 1.7(4) -3.0(3) 178.4(2) 176.6(2) -1.9(4) II -2(2) 6(2) -175(1) -178(1) -4(1) -2(2) 177(1) -176(1) 2(1) 3(1) 178(1) -1(2) 2(2) -177(1) -3(2) -178(1) 3(2) 18-1(2) -4(2) 175(1) -2(2) -149.8(3) 31.5(5) -3.4(5) 177.9(3) 130.3(3) -20.7(4) 49.2(5) -135.5(2) -160.1(3) 15.2(4) 18.0(3) 170.1(3) -9.8(4) 2.6(5) -179.3(3) -177.4(3) 2.5(5) -3.0(5) 179.0(3) -1.8(5) -178.3(3) 6.8(5) -3.1(4) 177.0(3) 172.6(3) -7.3(5) 2.0(5) -179.8(3) -178.5(3) -0.3(5) - 172.9(2) 7.2(5) -167.7(2) 158.1(9) -23(1) 4(1) -177.7(9) - 146.7(8) 10.9(9) -32(1) 152.0(9) 171(1) -6(1) -12(1) -177(1) 8(1) 1(1) -177(1) -4(1) -1(1) 3.9(2) -170.2(9) 177.3(9) -6(1) -176.8(8) -9(2) 167.3(9) -178.8(9) 6(1) -48(1) 137.5(9) 128.4(9) -46(1) 179.5(7) 179.6(8) mol a - 152.3(9) 3 5(1) -172.8(8) 157.6(8) -2.6(9) 24(1) -158.3(8) -175.7(9) 2.0(9) 2(1) 178.9(9) -1(1) 4(1) 178.5(9) 168.7(8) -178.1(8) 4(1) -0.6(9) 179.5(7) 12(1) -165.9(8) 177.4(8) 49(1) - 140.4(8) -126.4(8) 44(1) 179.6(6) -178.6(6) mol b 149.5(8) -3-5(1) 175.3(8) - 159.3(8) -0.5(9) -26(1) 157.7(7) 176.1(9) -0.6(8) 1(1) 178.0(9) -1.6(9) -3(1) 179.7(8) -1(1) 3(1) 1(1) -171.6(8) 179.4(8) -4(1) 1.3(8) -178.3(7) -9(1) 167.5(7) -176.0(7) 4(1) -47(1) 141.1(8) 130.5(8) -41(1) -177.5(6) -177.4(6) Assuming the benzene ring in planar (plane B), one can observe that the carbonyl group (C(1)-O(1)) has the largest distance to this plane caused by the coplanarity of the nitro group (plane N) to plane B. MOLECULAR ORBITAL CALCULATIONS Semiempirical quantum chemical calculations were performed for the molecule shown in Fig. 1 plus two related compounds. The AM1 procedure as implemented in AMPAC 5.0 (Semichem, Inc.) was employed. The electron density distribution and electronic spectra of compounds I to II were calculated. Figure 2 shows the net atomic charges for all the molecules being studied. The ring N atom has a small positive charge in all cases, while the -NO2 group N atom has a large positive charge as a result of polarization by the oxygen atoms. The positive charge for nitrogen induces a negative charge on the linked C atom.

Structure of 1-Acetyl-indoline and Derivatives 371 Table I. Atomic Distances with e.s.d's. (A) to the Least-Square Planes and Dihedral Angles Between the Planes ( ) for the Compounds to Plane A: O(l), N(l),,, Plane B:,,,,, Plane N:, O(2), O(3) mol a mol b Br 0(3) N(l) A-B A-N B-N 0.002(2) -0.007(3) 0.003(3) 0.006(2) -0.011(2) 0.007(2) -0.047(2) -0.038(2) -0.096(2) -0.087(3) 0.066(3) -0.198(3) 0.01(1) 0.0 0.02(1) 0.0 0.13(1) -0.03(1) 0.02(2) 0.02(2) 0.03(2) 0.1-0.008(3) 0.026(3) -0.011(3) -0.023(3) 0.041(3) -0.026(3) -0.276(1) 1.677(2) 0.097(3) 0.063(3) 0.075(3) 0.062(3) 0.936(3) -0.347(4) -0.117(4) 0.881(4) Dihedral Angles 45. 46.3(2) 2(6) 0.005(9) 0.006(9) 0.003(9) -0.02(1) 0.031(9) 0.02(1) 0.03 1.129(7) 0.460(7) -1.118(7) 0.065(7) -0.256(9) 0.668(9) -0.113(9) 0.02(1) 0.6 27.8(5) 54.7(7) 48.4(5) 0.021(8) -0.022(8) 0.000(8) 0.023(9) -0.023(8) 0.002(8) -0.013(1) -0.994(7) -0.338(8) 1.206(7) -0.049(7) 0.3-0.52(1) 0.005(9) 0.006(9) -0.3 26.5(4) 52.3(7) 49.2(5) 0.025(8) -0.016(8) 0.029(7) -0.016(8) 0.107(1) 1.048(6) 0.413(7) -1.074(7) 0.049(6) -0.242(8) 0.524(9) 0.002(8) -0.053(8) 0.34(1) 152.4(3) 48.6(6) 135.1(4) Fig. 2. Calculated net atomic charges for compounds to II.

372 Torres Moreno et al. Fig. 3. Calculated bond indexes for compounds I to II. Table II. Calculated and Measured Lowest Electronic Transitions for Compounds to II Compound Nature of the transition Wavelength (nm) Oscillator strength Measured peaks [5, 6] Compound Nature of the transition Wavelength (nm) Oscillator strength Measured peaks [5, 6] T -» T* *-» T* 7 -> f* K -> T* f -> i* 7 -» T* 7 -> T* - a* I -» T* - a*" i -> T* 322 301 296 242 332 316 286 236 347 338 333 268 351 322 0.0169 0.2030 0.0243 0.1435 0.2368 0.0449 0.0166 0.2101 0.0392 0.0571 0.0785 0.0384 0.0755 0.1503 _ 336 230 343 I II T -> f* i -> T* 7 -> T* - a*" T -> r* r -> T* 256 241 329 287 266 252 350 318 268 240 341 319 276 259 0.0155 0.2003 0.0279 0.0264 0.2908 0.1466 0.0622 0.1480 0.0174 0.2276 0.0379 0.0137 0.3125 0.0421 243 333 343 243 333 _ aas a result of the nonstrict planarity of the molecules, some mixing of quasi-r and quasi-r orbitals may appear.

Structure of 1-AcetyI-indoline and Derivatives 373 The O atom in the acetyl group has a negative charge, polarizing the neighboring carbon atom. Figure 3 displays the calculated bond indexes. The C Br bond is estimated as a single bond, the CO linkage is quasi a double bond, and NO has a bond index of 1 12as expected. The benzenoid ring shows an aromatic character and the difference between indoline and indol 5-membered rings shows an increase of half a bond where the double linkage is assumed (between atoms 2 and 3). Table II shows the lowest electronic transitions and a few measured peaks. The calculated values were obtained with the aid of configuration interaction (CI) and the AM1 routine. The CI calculation included the last 10 higher-occupied orbitals and the first 10 virtual orbitals. This generates ca. 2 X 10 5 microstates from which ~ 100 microstates are selected. The nature of the transitions, the wavelength, and the oscillator strengths are reported. All molecules show a first absorption at 320-350 nm. The last theoretical transition shown is at approximately 250 nm. There is a good correspondence between the measured peaks and the calculated transitions available. CONCLUDING REMARKS X-ray diffraction analysis was employed for the structural characterization of 1-acetyl-indoline and nitro and bromo derivatives; a bromo-nitro indol compound was also included in the study. The same and related compounds were examined by semiempirical quantum chemical calculations with the main purpose of providing the lowest electronic transitions and electron density distribution. ACKNOWLEDGMENTS We are gratefull to Prof. G. Goissis and Mrs.. C. A. Martins for providing the crystal samples. This work had financial support from CNPq and FINEP (Brazilian agencies). Certain of the results in this paper were developed with the assistance of AMP AC 5.0, a quantum chemistry program for Semichem, Inc. REFERENCES 1. Amit, B.; Ben-Efrain, D. A.; Patchomik, P. J. Am. Chem. Soc. 1976, 98, 834. 2. Goissis, G.; Erikson, B. W.; Merrifield, R. B. Proceedings of the Fifth American Peptide Symposium; John Wiley: New York, 1976, p. 559. 3. Goissis, G. Private communication. 4. All the crystal samples were provided by Prof. G. Goissis, Institute de Quimica de Sao Carlos, Universidade de Sao Paulo. 5. Pepato, M. T. Dissertation; University of Sao Paulo, 1985. 6. Martins,. C. A. Dissertation; University of Sao Paulo, 1989. 7. Sheldrick, G. M. SHELXS 86. In Crystallographic Computing 3; G. M. Sheldrick, C. Kruguer, and R. Goddard, eds.; Oxford University Press, 1986. 8. Sheldrick, G. M. SHELX 76: Program for Crystal Structure Determination; University of Cambridge: England, 1976.