1757
Organic and Biologicd Chemistry Infrared Intensities as a Quantitative Measure of Intramolecular Interactions. II1.ls2Further Monosubstituted Benzenes and Monosubstituted Durenes R. T. C. B r ~ w n l e e R. , ~ E. J. Hut~hinson,~ A. R. Katrit~ky,~ T. T. T i d ~ e l l , ~ and R. D. Topsom5 Contribution from the School of Chemical Sciences, University of East Anglia, Norwich, England, the School of Physical Sciences, La Trobe University, Melbourne, Australia, and the Department of Chemistry, University of Canterbury, Christchurch, New Zealand. Received September 5 , 1967 Integrated intensities for the v16 mode of 110 monosubstituted benzenes (with the substituent ring linked by halogen, oxygen, sulfur, nitrogen, or carbon) are tabulated together with u R ovalues for the substituents derived by a refined relation. Little variation of u R O occurs with solvent, but results for 11 monosubstituted durenes show that twisting of a noncylindrically symmetrical substituent decreases mesomeric interaction markedly. The uR0 values generally compare well with those found by other methods and discrepancies can be explained. The nature of substituent-ring interactions is discussed. Consideration of the u~ values by compound classes inter alia provides evidence for significant conjugative interactions in cyclopropylbenzene, and confirms recent conclusions on the variation of nitrogen-ring interaction in N-phenyl cyclic imines. Abstract:
O
P
revious work indicated that a precise correlation, formulated initially as eq 1' and later as eq 2,2 existed between A''', the square root of the integrated absorbance of the Y16 ring bands6 in monosubstituted benzenes, and u R o for the substituents. The measurement of infrared intensities promised2 to be a conve-
0.0075 A"' (1) uRO = 0.0079A"' - 0.027 (2) nient and reliable method for the determination of uR0 values, which are of great importance in the correlation and prediction of physicochemical properties. We have therefore extended our work on monosubstituted benzenes with the following main aims: (a) to further test the validity of, and if possible to further refine, eq 2; (b) to investigate the variation of u R 0 values with solvent and with steric hindrance; (c) to elucidate the nature of substituent-benzene ring interactions ; (d) to make available a wide range of uR0 values; (e) to illustrate the use of infrared intensity measurements in the clarification of specific problems involving substituent-ring interactions. There have been many indications that the quantitative failure of the Hammett relation to correlate precisely all types of reactions is a result of the differences in resonance demands of various reaction types and sites (for reviews see ref 7 and 8). Many multiparameter equations have been postulated to account for this uR
(1) R. T. C. Brownlee, A. R. Katritzky, and R. D. Topsom, J. Amer. Chem. Soc., 87, 3260 (1965). (2) R. T. C. Brownlee, A. R. Katritzky, and R. D. Topsom, ibid., 88, 1413 (1966). (3) University of East Anglia, Norwich, England. (4) University of Canterbury, Christchurch, New Zealand.
( 5 ) La Trobe University, Melbourne, Australia. (6) G. Herzberg, "Infrared and Rarnan Spectra of Polyatomic Molecules," D. Van Nostrand Co., Inc., Princeton, N. I., 1945. (7) C. D. Ritchie and W. F. Sager, Progr. Phys. Org. Chem., 2. 323 (1964).
behavior ; these equations can usually be written in a form equivalent to eq 3 (for recent explicit examples see ref 9). Accurate values for uI are log (k/ko) =
pig1
+
PRQR'
(3)
available for many substituents (see ref 10 and references contained therein); we believe that a large collection of reliable u R 0 values will be useful in further correlation work. For the estimation of the effects of steric hindrance we have investigated monosubstituted durenes. As regards specific problems, we have chosen (i) the interaction of a benzene ring with cyclopropyl rings compared with other benzene-cycloalkyl group interactions, and (ii) the variation of the interaction of a benzene ring with a lone pair located on a nitrogen atom forming part of a saturated heterocyclic ring with the size of this ring. We also recorded the intensities of the Y13 bands near 1500 cm-'; these correlate2 with uRo, but we defer further discussion until analogous work in progress on disubstituted benzenes is complete. Other workers have considered the intensities of other vibrations in monosubstituted benzenes; the intensity of the C-H aromatic stretching modes is directly related"-13 to the uI value of the substituent. However, the intensities of the C-H out-of-plane bending modes for monosubstituted alkyl- l 4 and halobenzenes l 5 show no simple (8) S . Ehrenson, ibid., 2, 195 (1964). (9) H. Giisten and M. Salzwedel, Tedahedron, 21, 173 (1967). (10) R. W. Taft, E. Price, I. R. Fox, I. C. Lewis, K. K. Andersen, and G. T. Davis, ibid., 85, 709 (1963). (1 1) E. D. Schmid, V. Hoffmann, R. Joeckle, and F. Langenbucher. Spectrochim. Acta, 22, 1615 (1966). (12) E. D. Schmid, ibid., 22, 1659 (1966). (13) F. Matossi and E. D. Schmid, Z . Naturforsch., 21a, 1300 (1966). (14) A. S. Wexler, Spectrochim. Acta. 21, 1725 (1965), and references
therein. (15) R. P. Bell, H. W. Thompson, and E. E. Vago, Proc. R o y . SOC. (London), A192, 498 (1948).
Brownlee, et ai. 1 Monosubstituted Benzenes and Durenes
1758
Table I. Spectral Data and Calculated and Literature Infrared solvent
i r ~ ' ,
PhH PhD PhF PhCl PhBr PhI PhIC12 PhJ+ PhOH PhOMe PhOEt PhOPrr PhzO PhOCOMe PhOCOCF3 PhOSOzMe PhOCF3 PhOH PhO-Na+ PhSH PhSMe PhSEt Ph2S PhSCOMe PhSCF3 PhS-Na+ PhSO8-Na+ Ph2S02 PhS02Me PhS03Me PhS02CI PhS02-Na+ PhzSO PhNDz PhNHMe PhNDMe PhNMe? PhNHEt PhNHBu" PhNHPri PhNEts PhN(CHz)z PhN(CHd3 PhN( CH2)4
CCl, CCl, CCI4 CCl, CCI4 CCI, CHC13 DMSO CCl, CCl, CCI, CCI4 CC14 CCI4 CCl4 CCl, CCI, DzO D20 CCI4 CCI, ccl4 CCI4 CCI4 CCl, D20 Dz0 CHC13 CHCls CCI, CC1, D2O CCI4 CCI4 CCI4 CCI, CCI4 CCl, CCI4 CCl, CCI, CCI, CCI, CCI,
0.00 0.00 0.341 0.217 0.231 0.221 0.118 0.281 0.402 0.428 0.439 0.428 0.364 0.235 0.234 0.264 0.250 0.424 0.593 0.195 0.250 0.192 0.189 0.081 0.00 0.334 0.00 0.064 0.069 0.087 0,108 0.00 0.065 0.467 0.522 0.523 0.533 0.520 0.536 0.533 0.571 0.382 0.552 0.628
PhN(CH2)j PhzNH Ph,N PhN(CF3)2 PhNHNHp PhdNHh PhNHOH PhNMeCOMe PhNHCOMe PhNO PhzNz PhNCO PhNCS PhNSO PhNCNPh PhN02 PhN?+BF,PhNDs+CIPhNDzMe+C1PhN D Mez+CIPhNMe3+C1PhNDCMeNDPh +C1PhMe PhEt PhPrn PhPr% PhBu' PhBu' PhCH(CHz)z PhCH(CHz)a PhCH(CHz)4
CCI, CCI,
0.474 0.504 0.438 0.132 0.487 0,441 0.222 0.408 0.413 0.071 0.056 0.403 0.354 0.087 0,461 0.174 0.304 0.183 0.149 0.136 0.149 0.585 0.099 0.103 0.109 0.115 0.115 0.125 0.175 0.124 0.136
Cornpd
cc1, CCI4 CBHIZ CCI, CHC13 CHC13 CHCli CCl, CCl, CCI, CCll CCl, CCI, CCI, D20 Dz0 Dz0 Dz0 DzO
calcd
Journal of the American Chemical Society
19Fa
0.00
UR'
values for Monosubstituted Benzenes
Lit. UR' React.*
-
0.001
-0.32 -0.18 -0.16 -0.14 0.00
-0.35 -0.20 -0.19 -0.12
-0.43 -0.43
-0.40
-0.341 -0.20' -0.141 -0.081 O.Oh
-0.41
-0.31 -0.21 -0.20 -0.18 -0.43 -0.60 -0.15 -0.17
Other
-0.45h -0.381 -0.32h
-0.17 -0.40 -0.66
-0.04h -0.381
-0.601
-0.24
-0.16" -0.07h
+Os 06'
+O, 07'1
+0.07 +0.16
+O, 081
+O. 16h
-0.48
-0.48
-0.48f
-0.54
-0.52
-0.501
0.00 -0.43
-0.30 +0.33 +0.02
0 . Oh?' -0.40h
-0.20
-0.06 $0.19
+O. 16f
-0.21h $0.32' +O. 08h -0.179 -0.070 + O . 13h
+o. 200 + O . 65*
-0.05h -0.09h -0.15 -0.14
-0.10 -0.09
-0.06,
-0. 17h
1 90:7 / March 27, 1968
1600band v e~~
1585 band v EA^
0 1594 1 1597 213 68 1585 1580 84 1574 139 41 1564 45 1566 1607 145 1603 208 1603. 233 1602 174 1592 114 1596 114 78 1593 85 1591 1594 71 1603 284 1588 324 1586 47 1585 62 1587 46 60 1582 17 1586 1584 9 1579 115 1610 3 1585 13 1589 20 12 1598 1585 21 2 1610 1583 13 1607 359 1607 338 1607 351 1604 346 1605 308 1604 344 1603 346 1607 293 1600 305 1601 540 1596, 1601 1599 320 1594 531 1589 191 1599 23 1505 325 1602 399 1605 71 1599 373 1602 234 13 1595 1586 26 1601 290 1595 200 3 1600 1595 461 42 1608 1591 128 77 1605 31 1602 23 1601 28 1599 1590 396 27 1605 24 1602 24 1605 20 1605 19 1604 25 1602 61 1604 33 1602 33 1603
0
1567
11
1560
11
1598 1590 1588 1589 1586
20 1 96 124 169 168
1585
91
1590
3
1575
0 3
1582
3
1585
23
1582 1578
38 45
1582 1584 1579 1569
59
1579 1566
26
1592
22
1587
64
1575
21
1591
13
1584 1586 1583 1585 1584 1581 1579 1581
4 7 4 5 5
Ad
0 30 2153 930 1044 961 348 1492 2940 3330 3500 3334 2421 1075 1067 1326 1205 3268 6290 764 1193 750 728 215 89 2065 100 172 185 233 304 80 178 3950 4897 4922 5098 4865 5170 5104 5852 2663 5461 7039 4045 4576 3489 405 4259 3523 963 3040 3115 189 155 2957 2182 235 3856 634 1726 689 492 428 490 6104 27 5 289 310 332 330 377 645 369 438
-5100 v
bande~~
c1/2a
1480 1479 1497 1489 1476 1474 1469 1474 1499 1498 1499 1495 1488 1493 1493 1489 1492 1493 1482 1481 1482 1482 1476 1499 1477 1474 1482 1480 1482 1481 1479 1478 1478 1501 1509 1505 1508 1506 1506 1505 1513
53 43 375 226 226 152 191 122 268 304 312 392 459 236 268 399 256 207 669 135 143 120 116 112 38 102 20 16 25 24 26 25 39 336
17.7 18.8 32.3 33.7 43.2 27.7 30.9 36.8 38.5 44.4 48.4 50.5 47.9 37.6 34.8 40.0 39.1 41.9 79.6 27.6 26.8 26.8 20.9 22.4 15.7 26.7 15.4 7.4 11.2 10.9 12.0 14.1 12.6 46.7
474 262 376 360 392 370
51.0 50.0 60.6 65.7 59.2 63.9
1495 1495 1492 1497
338 200 342
32.2 31.8 50.6
1494 1499 1499
107 358
23.1 42.3
1485 1513 1491 1484 1489
107 145 300 131 523
23.1 42.4 31.9 21.2 58.3
1500 1498 1498 1495
130
30.2
165
51.5
1496 1496 1497 1494 1494 1498
70 69 68 63 66
19.6 19.5 20.2 20.0 19.7
1759 Table I (Continued) Compd
Infrared solvent
PhCH(CH2)S PhCHnCHO PhCHnCN PhnCHn PhCHnOH PhCH,OMe PhCHBrn PhCHnCl Ph3CH PhCH(0CHn)n PhCHzBr PhCHClz Ph,C PhCH,ND3+CIPhCC13 PhCBr8 PhCFa PhCnFS Phn PhCHCHI PhCHCHCOOEt PhCHCHNOz PhCHCHN(CH2): PhCHO PhCOMe PhzCO PhCOOH PhCOOMe PhCOOEt PhCOCl PhnCn PhCCH PhCN PhCF(CF3)t PhCOH(CF3)z PhSFj PhC(OMe)3
--
&OR’,
calcd
19Fn
0.128 0.110 0.090 0.117 0.00 0.054 0.00 0.00 0.113 0.00 0.00 0.00 0.130 0.00 0.00 0.00 0.111 0.075 0.096
Lit. UROReact.b
-0.08 -0.07 -0.03
0.00 0.00
+o. 10
+O.O8J
0.11Q -0.10 -0.09 -0.03
0,050 0.loo
+O. 16
0.127 0.311 0.244 0.219 0.190 0.292 0.155 0.180 0.213 0.152 0.072 0.085 0,023 0.110 0.000 0.000
+0.27 +O. 19
$0.19 +0.30
+0.21 0. C4Q 0,020
+O. 18f
+o. 121
+o. 101 +o .02
-
Other
1600 band Y
fAc
1585 band Y
1601 33 1581 18 1587 1603 16 1589 1605 51 1586 1602 1608 4 1587 1603 1587 5 1603 3 1586 3 1587 1604 -0.12h 1599 82 1583 1610 2 1590 1602 3 1587 +o, 02h 1598 3 1586 23 1597 0.Oh 1607 1 1599 +o, 02h 1584 1 +O. 03h 2 1584 1602 33 +0.100 1611 15 1610 -0.09f 1598 22 1582 7 1576 1602 -0.03 1580 39 1604 15 1580 1600 213 1575 1598 81 1586 1601 77 1581 $0. 17h 1602 111 1580 +0.21h 1607 101 1586 55 1583 1603 1603 45 1585 +0,32h 1598 70 1585 1605 42 1575 +O. 0 8 h 11 1575 1599 +o. 22h 1600 12 1583 +0.06h 4 1593 1605 12 1605 +O. 07h 1597 3 -0.01h 1620 3 1604
e~~
7 5
12 3 4 5 3 17 2 3 3 2 2 4 13 45 28 71 38 61 98 15 32 47 7 10 6 3
1
-5100 Ad
band--
Y
e~~
100 80 398
1499 1498 1496 1497 1497 1495 1497 1496 1494 1497 1499 1494
113 130 36 40 47 46 270 17 49 25
60
1501
15 61 317 198 260 144 277 387
1499 1492
392 314 241 339 95 150 99 90 324 55
1800 1150 940 746 1598 526 670 899 509 190 228 109 313 85 77
1502 1484 1496 1498 1497 1499 1480 1491 1488 1496 1493 1491 1481 1501 1489 1492 1502 1504 1488
56
20.5 18.4 31.2 14.0 15.3 13.8 14.3 32.8 15.5 13.1
65
15.1
18 104 98 54
9.5 20.4 16.2 17.2
48 2 4 0 33 144 11 7 126 118 74 38 36
16.7 3.0 5.1 0 11.6 29.4 8.1
71
6.6
25.0 20.3 17.7 18.3 18.6 19.8
1gF values from ref 34,or calculated from figures for dilute solution in cyclohexane using the formulas therein, and ref 10. Zero values are taken from ref 32. * Reactivity values collected in ref 34,and taken from J. Hine, J . Amer. Cliem. SOC.,82,4877(1960). CA is the peak extinction coefficient; CA = Am,,/c/. d A is the integrated intensity of the 1600- and 1 5 8 5 - ~ m -band; ~ A = ZA/c/. e E is an estimate of the integrated intensity given by e = ~ A A u ‘ / ~1. Reactivity value from R . W. Taft, S . Ehrenson, I. C. Lewis, and R. E. Glick, J . Amer. Cliem. Private communication by R. W. Taft and W. A. Sheppard giving SOC.,81, 5352 (1959); values are 2.0U R ~ , Reference 63 IgFvalue. 19F values. 1 g F values from F. S. Fawcett and W. A. Sheppard, J. Amer. Cliem. SOC., 87,4341(1965). Q
variation with the usual substituent parameters although a limited correlation with dipole moments has been reportedI6 (see also ref 17). Russian worker^^*,^^ have correlated the logarithms of the intensities of the Raman bands near 1600 cm-I for monosubstituted benzenes with Hammett d constants; however, we found no precise relation between the reported Raman and our measured infrared intensities. It is of interest that the effect of substituents on the integrated intensity of the vCN in substituted phenyl cyanides is better correlated by reactivity parameters than the effect of substituents on the v C x frequency.*O
Experimental Section Vapor phase chromatography and/or melting points were used as criteria for purity throughout. The monosubstituted benzenes were mainly commercial samples or simple derivatives of them. The fluorinated compounds were kindly supplied by Dr. W. A. (16) Y. Kakiuchi and T. Shimozawa, Proc. Intern. Symp. Mol. S f r u c f .Spectry. Tokyo, C215 (1962); Chem. Abstr., 61, 3817 (1964). (17) A. R. H . Cole and A. J. Michell, Spectrochim. Acta, 20, 739 (1964). (18) Y. S. Bobovich and N. M. Belyaevskaya, O p t . Spectry., 19, 111 (1965). (19) Y. S. Bobvich, ibid., 20, 136 (1966). (20) 0. Exner and K. Bozek, Tetrahedron Letters, 1433 (1967).
Sheppard, Experimental Station, Du Pont. Benzene iodine dichloride21a and N-/3-phenylvinylpiperidine2*were made by literature methods. Amino compounds were deuterated on nitrogen by shaking twice with excess deuterium oxide, and the purity of the distilled products was checked by the absence of N-H bands. N-Phenylazetidine was preparedn3 by the aluminium chloride catalyzed decomposition of 3-amino-1-phenoxy-N-phenylpropaneusing the general method24 employed for the preparation of chromans from the corresponding diphenoxypropanes. The other N-phenylimines were prepared by standard methods. Hydroxy-, methoxy-, nitro-, chloro-, bromo-, iodo-, and cyanodurenes were kindly donated by Professor G. Illuminati, University of Rome, and were used as supplied. Commercial pentamethylbenzene was found to be pure by vpc. Aminodurene was obtained from dinitrodurenez5by reduction t o aminonitrodurene,*edeamination, and further it was purified by recrystallization, fractional sublimation up to 80” (0.2mm), and further recrystallization from 80% ethanol, to mp 65-72’ (lit.28 74-74.5”);nmr ex(21) A. I. Vogel, “Practical Organic Chemistry,” 3rd ed, Longmans, Green, and Co., London, 1961 : (a) p 541 ; (b) p 572 (22) C. Mannich and H. Davidsen, Chem. Ber., 69,2106 (1936). (23) L. W. Deady, R. E. J. Hutchinson, R . D. Topsom, and J. Vaughan, to be published. (24) L. W. Deady, R. D. Topson, and J. Vaughan, J . Chem. S O C . , 5718 (1965). (25) A . H. Blatt, Ed., “Organic Syntheses,” Coll. Vol. 11, John Wiley and Sons, Inc., New York, N. Y., 1943, p 254. (26) C. E. Ingham and G . C. Hampson, J . Chem. Soc., 981 (1939). (27) G . Illuminati, J . Amer. Chem. Soc., 74, 4951 (1952). (28) B. M. Wepster, Rec. Trau. Chim., 76, 357 (1957).
Brownlee, et at.
Monosubstituted Benzenes and Durenes
1760 amination then showed approximately 5 % impurity. Dimethylaminodurene was prepared from the primary amine by reaction with trimethyl phosphate;2lb the product was steam distilled directly from the basified reaction mixture; nmr and infrared spectra showed no N-H absorption. Purification by sublimation (0.5 mm, 100") and then recrystallization from 50% ethanol gave white plates, mp 45-51" (lit.28 52-53"), with no impurities visible in the nmr. Fluorodurene was obtained aia the Schiemann reaction 2Q on aminonitrodurene followed by reduction and deaminationlg and purification by chromatography on alumina, sublimation (0.2 mm, 60"), and finally recrystallization from 50% ethanol, to mp 5558" (lit.l# 54.5-55"); it showed no impurities in the nmr. For some durenes, the lower band appeared as a shoulder on other bands at lower wave number, and large base-line corrections were needed. For many of the durenes insufficient material was available for more than a single solution, although duplicate determinations were made on this solution (All2 reproducible to f1 unit); where duplicate solutions were available the All2 values were also reproducible within f1 unit. Carbon tetrachloride, cyclohexane, and 2-propanol were spectroscopic grade solvents. Chloroform was purified by passing it through alumina immediately prior to use; dimethyl sulfoxide was dried over CaH2. Deuterium oxide (Imperial Chemical Industries Ltd.) was used without further purification. The spectroscopic technique for the nonpolar solvents in the sodium chloride cells and the integration procedure for the 1600- and 1 5 0 0 - ~ m -bands ~ were as previously reported.2 The spectra of solutions in deuterium oxide or dimethyl sulfoxide were recorded using a balanced pair of Irtran I1 cells (-0.05 mm). Spectra when recorded in these cells were superimposed upon the interference pattern which altered in position as the cell heated in the spectrometer. Previous workers" have subtracted such interference patterns, but we did not find this procedure satisfactory. The interference pattern can be removed by grinding one plate in each cell to a mat surface using fine carborundum powder. The cells then have a constant base line, even when the cell heats up; however, the cell length can still be measured in air using the interference method. The reproducibility of A1/2is f1 for most cases in nonpolar solvents, except that where the compound was sparingly soluble or there were interfering bands (e.g., PhIC12, PhNO2, and compounds containing the groups C=C or C=O) the reproducibility fell to f 4 in A'/2. For the polar solvents, balancing is not possible, and the error is & 4 in All2. For compounds having more than one benzene ring, the A , E A , and e 1 / 2 values have been divided by the number of benzene rings.
data for the durenes. Table 111 records the solvent dependence for the 1600-cm-l band intensities of selected compounds. Table 111. Variation of Integrated Intensities (All2 Values) with Solvent Substituent
C6H12
CCl4
NMe2 OMe OH F Br c1 NO9 Me CN
69.0 58.3 52.3 47.4 31.7 29.5 22.2 16.0 15.9
71.4 57.7 54.2 46.4 32.3 30.5 25.2 16.6 15.1
CHC13 (CH3)KHOH 70.3 55.8 55.9 45.7 31.2 30.2 22.8 18.6 15.4
68.7 57.7 60.1 46.6 31.2 29.3 21.7 16.7 14.2
Few precise intensity data for these bands have been reported in the literature. Wexler14 measured the integrated intensities of alkylbenzenes; his values (Me, 280; Et, 280; i-Pr, 310; sec-Bu, 340; t-Bu, 430) agree to within ca. 5 7 , with our values except for t-butyl. Earlier measurements of values,31 made on a prism instrument, are generally about 7 0 z of the values now reported in Table I. The i u R 0 values given in this table are those calculated using eq 5.
Discussion Comparison of Measured with Previous uRO Values and Refinement of u R 0 Intensity Relationship. A detailed comparison of u R 0 values derived from our previous* eq 2 with all the literature values available discloses the following results. (i) Agreement within 0 . 0 3 ~ ~ unit " with both fluorine nmr and reactivity values where these are available for following substituents: NMe2, ND2 ("*), OMe, OH, F, Ph, OAc, CF3, CH2Cl, CC13, CHO, COMe, C02Me, NOn. The g R 0 from eq 2 for the subResults stituent 0- agrees excellently with the fluorine nmr Table I collects the data for the 1600- and 1 5 0 0 - ~ m - ~ value, but shows a discrepancy of 0.05 with the reacbands for the monosubstituted benzenes now reported, tivity value. Slightly greater discrepancies (up to 0.05 and includes values from the previous paper:2 it units) are shown between the infrared and the fluorine records band positions, extinction coefficients, and innmr values for the substituents OPh, Me, Et. tegrated intensities together with literature and cal(ii) The infrared-derived u R 0 values are larger than culated g R o values. Table I1 gives the experimental the fluorine nmr g R ovalues by 0.04-0.09 unit for the substituents C1, Br, SH, and SMe. We believe that this discrepancy is due to interactions involving d orbiTable 11. A Values for Monosubstituted Durenes Compared with UR' Values for Corresponding Benzenes tals in the corresponding para-substituted fluorobenzenes used for the nmr determinations; previous eviSubFrequency, A URo dence for such interaction^^^ is confirmed by work prestituent Solvent cm-l (durene) (benzene) sented in an accompanying paper.33 For the sub1634, 1572 1063 0.341 F CCl4 stituents C1 and SMe, our uR0 values are in good agree1634, 1572 984 0.341 CIH12 ment with reactivity values; unfortunately, no such 1612, 1560 472 0.217 CI CBHlZ 1607, 1548 738 0.231 Br CCl, data are available for SH, and alternative reactivity 1608,1550 655 0.231 CsHiz values for Br are widely divergent (0.14, 0.19; see ref 1604, 1538 576 0.221 I CBHl2 34 and Table I). 1624 87 0.174 N0z CCl4 (iii) Significant overlap of the ring mode with 1616, 1566 875 0.428 OMe CBH12 1626, 1574 1940 0.402 OH CCl4 the substituent vibration at 1631 cm-' for styrene may 1604, 1566 540 0.533 MezN CCI4 invalidate the infrared-derived u R o value for the group Me CN
CsHiz CBHlZ
1608, 1570 1606
147 84
0.099 0.085
(29) G. Grassini, G. Illuminati, and G . Marino, Gazz. Chim. Ifal., 8 6 , 1138 (1956); Chem. Absrr., 52, 1937a (1958). (30) C . A. Swenson, Specfrochim. Acta, 21, 987 (1965).
(31) A. R. Katritzky and J. M. Lagowski, J . Chem. Soc., 4155 (1958). (32) R. W. Taft and J. W. Rakshys. Jr., J . Amer. Chem. Soc., 87, 4387 i1965). (33) P. J. Q. English, A. R. Katritzky, T. T. Tidwell, and R. D . Topson, J . Amer. Chem. Soc., 90, 1767 (1968). (34) R. W. Taft, E. Price, I. R. Fox, I. C. Lewis, K. I OS02Me > OAc 2 OCOCF,. Evidently, inductive withdrawal is of lesser importance than 7~ overlap in hindering the mesomeric donor properties of oxygen because COR (UR' of OCOMe = 0.235) is more effective than S02R (uR0 of OSOzMe = 0.264) in reducing the u R o of OH (0.402); however, OCF3 also has a low value (0.250). The 0substituent shows a value of uR O considerably enhanced compared with that for OH (0-,0.593; OH, 0.424 for DzO solution), as expected from the great conjugative ability of anionic oxygen. Sulfur Linked. The divalent sulfur compounds show values which are smaller than those of the analogous oxygen derivatives by 0.18-0.26~~'unit. The smaller conjugative effect of sulfur is in contrast to its superior nucleophilicity over oxygen; however, when acting as nucleophiles, it is the u electrons which are involved. The poorer availability of the sulfur ?r electrons compared with oxygen is due partly to less overlap resulting from the large size of the 3p orbitals, but there is also some cancellation due to acceptance of electrons by the sulfur atom into its d orbitals, as will be discussed later. 3 3 Among oxygenated sulfur-linked substituents, the groups SOzO-, S02Ph, SO2Me, SO20Me, SOzCl represent a series of groups of increasing electron-attracting power ( u R 0 = 0.00 [DzO], 0.064, 0.069, 0.087, 0.108), as would be predicted; the relative positions of Me and Ph in this series confirm that electron withdrawal from the benzene ring is now occurring, In the lower oxygenated state only SOO- (uR' = 0.00) and SOPh (0.065) are available; there are no significant differences between these values and those in the higher oxidation state. Nitrogen Linked. (i) Alkylanilines. Alkylation of aniline causes an interesting variation in u R 0 values, which probably reflects both electronic and steric influences. There is no significant effect due to deuterium substitution on nitrogen ("Me and NDMe have u R 0 = 0.522 and 0.523, respectively), but alkyl substitution gives more complex behavior (ND2, 0.467 ; NDMe, 0.523; NMe2, 0.533) in which the difference between NDMe and NMez is surprisingly small and may represent a conformational preference. Increasing the size of the alkyl group in the secondary amines has but little effect ("Et, 0.520; NH-n-Bu, 0.536; NH-i-Pr, 0.533), but diethylaniline shows a significantly higher value (0.571) than that of the dimethyl analog (see below). Nitrogen Linked. (ii) Cyclic Imines. We studied N-phenyl-substituted cyclic imines because of recent i n t e r e ~ t . Comparison ~~~~~ of the oscillator strengths of the two readily accessible absorption bands in the ultraviolet spectra suggested7I that the nitrogen-phenyl ring interaction increased as the size of the imine ring was varied in the order three < six < four < five, and that (70) F. M. Beringer and S. A . Galton, J . Org. Chem., 31, 1648 (1966). (71) A . T. Bottini and C. P. Nash, J . Amer. Chem. Soc., 84, 734 (1962) (72) C. P. Nash and G . E. Maciel, J . Phys. Chem., 68, 832, (1964).
the resonance interaction for N,N-dimethylaniline was similar to that for N-phenylazetidine. Since the nitrogen configuration in an azetidine cannot be trigonal, this result was interpreted7I as evidence for an essentially tetrahedral configuration about the nitrogen atom in N,N-dimethylaniline and related amines. Carbon- 13 magnetic shielding results72confirmed the relative order of resonance interactions for the three-, five-, and sixmembered ring imines measured, and N,N-diethylaniline also showed a marked increase in interaction over N,N-dimethylaniline, near to that for N-phenylpyrrolidine. The relative basicities of dimethyl- and diethylaniline are in the opposite sense, probably due to steric inhibition to hydrogen bonding in the free diethyl compound. The ionization potentials73 and rates of electrophilic s u b s t i t ~ t i o n ~also ~ ' indicate enhanced electron availability in the diethylaniline ring, and results mentioned above confirm this. We now find that the carbon-13 magnetic shielding results, thef sums, and the exhaltations of molar refraction (Table IV) all correlate reasonably well with the Table IV.
UR' Values from the Integrated Intensities ( A ) of the v18 Bands in Monosubstituted Benzenes"
Substituent
A 5098 58526 2663 5461 703Yb 3Y19b
-NMe2 -NEti -N(CH2)2 -N(CH*)I -N(CHz)n -N(CHz), ~
*UR'
0.53 0.57 0.38 0.55 0.63 0.47
Cpara-Cmetaf sum
12.Y 13.6 7.4 13.9 10.3
0.33 0.34 0.20 0.33 0.37 0.26
ARD 1.49 1.58 0.43 1.60 1.64 0.96
~-
13Cchemical shift differences, the sum of the oscillator strengths (f sum), and the exhaltation in molar refraction are also listed (from ref 71 and 72). An additional peak in the spectrum of N-phenylpyrrolidine and shoulders in the other two spectra occurred at 160&1605 cm-l. The intensities were included in the ~ total since they will be almost entirely derived from the Y , absorptions by Fermi resonance. In parts per million with reference to benzene. a
infrared-derived uR0 values, indicating a compound dependence on resonance interactions. The u R 0 value for N-phenylpyrrolidine is still higher than that for N,Ndiethylaniline. Steric interactions between the a-hydrogens on the imine ring and o-hydrogens on the phenyl group7l probably cause a preferred conformation in Nphenylpyrrolidine favorable for interaction of the nitrogen lone pair with the aromatic nucleus.74b The increase in interaction in N-phenylpyrrolidine over N,Ndiethylaniline may thus result from a steric enhancement and be broadly analogous to the increased interaction between alkyl groups and the nucleus in acenaphthene compared to 1,%dimethylnaphthalene where the substituents are free to rotate.73 a-Hydrogen-ohydrogen interactions in N-phenylpiperidine should result in a preferred conformation less favorable for interaction7' and the lower u R 0 value found confirms (73) P. G . Farrell and J. Newton, ibid., 60, 3506 (1965). (74) (a) R . P. Bell and E. N. Ramsden, J . Chem. SOC.,161 (1958). (b) Recent works, e$., ref 61 and 62, have suggested that most of the
interaction in aniline and related compounds arises from repulsion between the unshared electrons on the nitrogen atom and the r system of the ring rather than from delocalization. The present work measures the actual electronic disturbance in the ring and can be interpreted equally well by either concept. (75) A. Fischer, W. J. Mitchell, J. Packer, R. D. Topsom, and J. Vaughan, J . Chem. Soc., 2892 (1963).
Brownlee, et al. J Monosubstituted Benzenes and Durenes
1766
this (cf. the cyclopentyl- and cyclohexylbenzene comparison ; see later). The sterically preferred conformation in N-phenylazetidine and N-phenylaziridine should again be the most suited for electronic interaction, and here the smaller effects observed probably result from the increased s character of the lone-pair orbitals. We conclude that the similar electronic interactions found for N-phenylazetidine and N,N-dimethylaniline are not unambiguous evidence for similar configurations about the nitrogen atoms, and that dissimilar configurations are favored by the infrared data. Nitrogen Linked. (iii) Further Tricoordinated Nitrogen. Phenylation at the nitrogen causes irregular behavior (NH2,0.467; NHPh, 0.504; NPh2, 0.438), but trifluoromethylation results in a large reduction in uRO [to 0.132 for N(CF&]. The groups NHNH2, "OH, and NHNHPh show ',6 values of 0.487, 0.222, and 0.441, respectively, which indicate that whereas substitution in the amino group of NH2 and NHPh causes small variation only, hydroxylation has a large effect. Acylation also reduces the ring conjugation of amines, but the groups NHAc and NMeAc are still powerful electron donors with u R 0 values of 0.413 and 0.408, respectively. Sulfonamido derivatives were unfortunately insufficiently soluble for determination. Nitrogen Linked. (iv) Multiply Bonded and Cationic Substituents. The N=O and N=NPh groups both have rather small u R o values (0.071 and 0.056, respectively). The direction of the effect is not defined by the results for the monosubstituted compounds ; we intend to deduce this from suitable polysubstituted derivatives, The substituents with cumulated double bonds N=C=O, N=C=NPh, and N=C=S show comparatively large effects (uR0 = 0.403, 0.461, 0.354, respectively); we believe that these substituents are resonance donors, as indicated by previous workers,7fibut plan to investigate polysubstituted compounds to confirm this (cf. ref 33). However, in thionylaniline, the substituent NSO has u R o of only 0.087. The triply bonded diazonium group N+=N has the high u R o of 0.304; resonance withdrawal by this group is considerably greater than by NO2 ( u R O = 0.174). Among cationic nitrogen derivatives, we have measured ND3+,NMeD2+,NMezD+,and NMe3+which show values of 0.183, 0.149, 0.136, and 0.149, respectively. These groups are electron donors by the resonance effect as is indicated by results for para-33and meta-disubstitutedfi4compounds. This evidence and the implication of these results are discussed later.33 The smaller magnitude of the effect when H is replaced by Me is probably a result of solvation being most effective in dispersing charge in the NH3+ compound. The amidinium group N+D=CMe-NDPh shows a strong effect (mRo = 0.585), indicating considerable electron donation to the ring. Carbon Linked. (i) Alkyl and Cycloalkyl Groups. The small increase in electron donor ability in series Me < Et < i-Pr < t-Bu indicates that any hyperconjugative release from a C-C bond is at least as important as that from a C-H bond. The electronic interaction of a cyclopropane ring with adjacent unsaturated groups has attracted much attention77 including theoretical,78 spectral,79and reac(76) I
