266 J. Org. Chem., Vol. 36, No. 2, 1971
CHARTON
The Nature of the Ortho Effect. VII. Nuclear Magnetic Resonance Spectra n/IARVIN CHARTON
Department of Chemistry, School of Engineering and Science, Pratt Institute, Brooklyn, New York 11106 Received December 18, 1969 Twenty-seven sets of nmr chemical shifts and related data for ortho-substituted benzenes and naphthalenes were correlated with the equation QX = am.x ~ U R . X $rv h and the extended Hammett equation QX = au1,x ~ U R , X h. Significant correlations were obtained for 22 of 26 sets correlated with the former equation and 24 of 27 sets correlated with the latter equation. The results obtained show that $ is not significant in most of the sets studied and that better correlation is generally obtained with the latter equation than with the former. There is no steric effect exerted by the ortho substituents in most of the sets studied. The substituent effect, thus, is purely electrical. The composition of the electrical effect depends upon structure and solvent. For the chemical shifts of aromatic ring protons, the resonance effect predominates. I n the majority of the sets studied, the value for the unsubstituted compound does lie on the correlation line.
+
+
+
+
I n continuation of our studies1-6 on the nature of the ortho effect, it seemed of interest to investigate nmr spectra. A number of authors have attempted the correlation of nmr data with the simple Hammett equation Qx =
PUX
+h
(1)
Thus, Bray and Barnes’ found a linear correlation between the C135pure quadrupole resonance frequencies in substituted dichlorobenzenes, including ortho-substituted compounds, and Hammett substituent constants. For the ortho-substituted compounds, substituent constants were defined from the ionization constants of 2-substituted benzoic acids. A correlation be tween the chemical shifts of ortho protons in substituted benzenes and the up constants was reported by Dieh18 and Kondo, et U L , ~report the correlation of the infinite dilution chemical shifts of 2-substituted benzoic acids with up and with the Taft uo* constants The definition of uo constants from the OH chemical shifts of 2-substituted phenols has been proposed by Traynham and his coworkers.lOlll The correlation of OH chemical shifts for 2-substituted phenols with bo* has been reported by Dietrich, Nash, and Keller.12 The NH chemical shifts of 2-substituted anilines have been correlated with both up and a, by Lynch, MacDonald, and Webb.Ia The chemical shifts of the S ring protons of 2-substituted N4-acetyl-N1-phenylsulfanilamidesare said to be correlated by the uo* constants according to Cammarata and Allen.14 The proton and 13Cchemical shifts in 2-substituted pyridines are correlated with C T ~ by Retcofsky and l\lcDonald.16 Infinite dilution (1) M. Charton, J. O r g , Chem., 34, 278 (1969). (2) M. Charton, J. Amer. Chem. Sac., 91, 615 (1969). (3) M. Charton, ibid., 91, 619 (1969). (4) M. Charton, ibid., 91, 624 (1969). (5) M . Charton, ibid., 91, 6649 (1969). (6) M . Charton and B. I. Charton, Abstracts, 4th Mid-Atlantic Regional Meeting of the American Chemical Society, ’Washington, D. C., Feb 1969. (7) P. J. Bray and R . G . Barnes, J . Chem. Phys., 21, 551 (1957). (8) P. Diehl, Helu. Chim. Acta, 44, 829 (1961). (9) Y. Kondo, K. Kondo, T. Takemoto, and T,Ikenoue, Chem. Pharm. Bull., 14, 332 (1966). (10) J. G.Traynham and G. A . Knesel, J . Org. Chem., 91, 3350 (1966). (11) M. T. Tribble and J. G. Traynham, J. Amer. Chem. Soc., 91, 379 (1969). (12) M.W. Dietrich, J. S. Nash, and R. E. Keller, Anal. Chew., 38, 1474 (1966). Lynch, ‘I. B. C. MacDonald, and J. G. K . Webb, Tetrahedron, (13) B. & a4, 3595 (1968). (14) A. Cammarata and R . C: Bllen, J. M e d . Chern., 11, 204 (1968). (15) H. L. Retcofsky and F. R. McDonald, Tetrahedron Lett., 2575 (1968).
+
chemical shifts of substituted benzenes were correlated with the extended Hammett equation &x = am.x f
@UR,X
+h
(2)
by Hayamizu and Yamamoto.lG I n all of this work, there has been no systematic attempt to determine whether or not steric effects are present or with the exception of the work of Hayamizu and Yamomoto to ascertain the composition of the electrical effect. It will be useful at this point to review our method6 for determining the presence or absence of steric effects. There are four cases of interest to us. They are the following. (1) The steric effect obeys a linear free energy relationship. Then using a suitable steric parameter, we may write an equation including both electrical and steric effects such as QX
=
+
~UI,X
@UR,X
+ $bx + h
(3 )
where 01 is a measure of the localized electrical effect, CTRis a measure of the delocalized electrical effect, and f x is a measure of the steric effect. As a steric effect parameter, we have chosen the van der Waals radius of that atom or group of atoms which is bonded to the benzene ring. Thus, we have the expression &x = a m , x
+
+ $rv,x + h
~ U R , X
(4 )
(2) The steric effect does not obey a linear free energy relationship. We may then write for any particular datum in the set Qx = ~ U I . Xf DUR,X f s x h ( 5)
+
where Sx is the steric effect of the X substituent and is independent of any linear free energy relationship. (3) The steric effect is constant. I n this event &x = au1.x f P ~ R , xf h’ (6) where h’=h+Sx
(7)
(4) The steric effect is negligible or nonexistent. Then &x = ( Y U I , ~f P ~ R , xf h (2)
Equations 2 and 6 are equivalent. In order to detect the presence or absence of a steric effect the data are correlated with eq 2 and 4. Successful correlations with eq 4 are not in themselves sufficient to imply the existence of case 1. Conclusive (16) K . Hayamizu and 0. Yamamoto, J. ddol. Spectrosc., 29, 183 (1969).
THENATUREOF
THE
J. Org. Chem., Vo.. 36,No. 2, 1971
ORTHOEFFECT.VI1
267
TABLE I DATAUSEDI N CORRELATIONS 13. 6 sulfanilyl ring protons. 2'-Substituted iV4-acetyl-N1-phenyl1. a0. Disubstituted benzenes (PrZ)? "2, 68; OH56; Oble, sulfanilamides (THF):* MeO, 6.0; C1, 4.0; Br, 3.7; I, 3.5; 42; F, 2.5; Me, 17; C1, - 5 ; Br, -22; CN, -35; I, -41; NOn, -1.0. C02Me, -74; NOn, -98. 14. T ~ - ~ ISubstituted ~ . mesitylenes (Prz):' F, 7.85; Cl, 7.74; 2. 60. Disubstituted benzenes (CCl,, 35'):b Me", 0.80; Br, 7.68; I, 7.62; OH, 7.90; NH2, 7.98; NOz, 7.81; H, NHZ, 0.75; OH, 0.52; OMe, 0.47; Me, 0.21; Et, 0.18; 7.81. i-Pr, 0.16; tert-Bu, -0.02; C1, -0.03; CHZC1, -0.05; 15. Substituted durenes (Pr2):7 F, 7.91; C1, 7.76; Br, CH2Br, -0.18; Br, -0.18; I, -0.35; CN, -0.35; Ac, 7.71; I, 7.62; OH, 7.92; N H , 8.07; NOz, 7.95; H, 7.88. -0.60; COZMe, -0.67; NOZ, -0.93. 16. &Ie. 2-Substituted toluenes (neat, 11-12'):k NOZ, 1.09; 3. A&,. Substituted benzenes (c-CJllz):c F, 18.5; Cl, -1.2; CN, 0.99; C1, 0.78; Me, 0.61; OH, 0.76; NH2, 0.37; H, 45.3; "Men, Rr, -13.4; I, -24.0; OMe, 26.0; "2, 0.75. 36.0; CHO, -34.8; NOz, -56.9. 17. sM0. 2-Substituted toluenes (Ph, ll-12')+ NOz, 0.80; CN, 4. 60. Substituted benzenes (CCl,):d NOZ, -95.2; COC1, 0.73; C1, 0.71; Me, 0.61; OH, 0.69; NHz, 0.39; H, 0.71. -84.0; COBr, -80.1; SOzC1,e -76.5; COZMe, -71.3; 18. 2-Substituted toluenes (pyridine, ll-12'):k NO?, 1.14; CO2-i-Pr, - 70.2; COz-i-Bu, - 71.5; Ac, - 61.9; COEt, CN, 1.02; C1, 0.85; Me, 0.74; OH, 1.11; NHz, 0.88; 13, -62.5; CHO, -56.1; S02Me, -60.4; CC4, -63.8; 0.81. CN, -36.1; I, -38.8; Br, -18.3; C1, -2.6; OAc, 25.2; 19. &Ie. 2-Substituted toluenes (dioxane, 11-12'):k NOZ, 1.18; OMe, 48.4; OH, 55.8; NHz, 74.6; "Me, 79.5; NMez, CN, 1.12; C1, 0.91; Me, 0.77; OH, 0.74; NH2, 0.61; H, 65.9; Me, 20.1; tert-Bu, -1.9. 0.89. 5. 6 ~ 1 . 1-Substituted 3,4-dimethoxybenzenes (c-C&z) :I "2, 20. Gnrc. 2-Substituted toluenes (CC,, 11-12')+ NOZ, 1.16; 1.09; OMe, 0.80; Me, 0.62; H, 0.47; Br, 0.35; CHO, CN, 1.11; C1, 0.93; Me, 0.81; OH, 0.77; NHz, 0.58; H, -0.11; CO2Me, -0.28; NOI, -0.37. 0.90. 6. ~ R o . 1-Substituted 3,4-dimethoxybenzenes (C-CeHlz) :f NHz, 21. soH. 2-Substituted phenols (MezSO, 28'):' Ale, -9.14; 1.17; OMe, 0.96; Me, 0.62; H, 0.47; Br, 0.31; CHO, Ph, -9.38; C1, -9.96; Br, -10.14. -0.05; C02Me, -0.35; NOZ, -0.52. 22. sou. 2-Substituted phenols (MeZSO, 40'):" F, 9.70; C1, 7. S a l . !&Substituted naphthalenes (C-C&):~ NHz, 0.43; 10.00; Br, 10.07; I, 10.20; Not, 10.8; Cn, 10.97; CFa, OMe, 0.25; Me, -0.13; H, -0.50; C1, -0.53; Br, -0.66; 10.44; Me, 9.10; Et, 9.07; Pr, 9.06; i-Pr, 9.07; sec-Bu, CN, -0.83; Ac, -1.12; CHO, -0.96; C02Me, -1.23. 9.03; tert-Bu, 9.17; ViCHz, 9.19; PhCH2, 9.29; CHZOH, 8. 6H1. 2-Substituted naphthalenes (c-CeH1Z):g "2, 0.50; 9.18; Ph, 9.46; CHO, 10.75; Ac, 11.97; Bz, 10.61; COzMe, OMe, 0 16; Me, -0.09; H, -0.16; C1, -0.18, Br, -0.26; 10.55; OH, 8.70; OMe, 8.76; OEt, 8.66; NHAc, 9.29; CN, -0.32; Ac, -0.78; CHO, -0.66; C02Me, -0.70. NMe2, 8.78; MeS, 9.59; MeSO, 10.50. 9. 6 u ~ . 2-Substituted 6-methoxynaphthalenes (CC14):u NHz, 23. 6oH. 2-Substituted phenols (hexamethylphosphoramide, 0.44; OMe, 0.32; Et, -0.17; 11, -0.44; Br, -0.56; 40'):n H, 10.30; Me, 10.22; Et, 10.20; Pr, 10.18; i-Pr, Ac, -0.98; COZMe, -1.17. 10.22; sec-Bu, 10.17; terf-Bu, 10.33; c-CGH11, 10.15; Ac, 10. 6na. 2-Substituted 6-methoxynaphthalenes (CClr):g NHz, 11.88; Br, 11.27; CHO, 11.67; I, 11.35; MeO, 9.92; NOZ, 0.45; OMe, 0.36; Et, 0.08; H, -0.03; Br, -0.11; Ac, 12.1; Ph, 10.57. -0.64; COZMe, -0.68. 24. ."6 2-Substituted anilines (Me2S0, 37'):" Me, 278.0; OMe, 276.0; OEt, 274.0; C1, 312.0; Br, 312.0; NOz, 11. ana. 5-Substituted benzo[b]thiophenes (CDClS):* NHz, 0.75; OH, 0.61; OMe, 0.54; Me, 0.35; OAc, 0.34; I>, 440.0. 0; OSOZRIIe,e 0.07; C1, 0.07; CHzOII, 0.09; CHzCI, 0.01; 25. 7O)lc. 2-Substituted anisoles (CClr, 30'):p Me, 6.35; NHz, Br, -0.10; CN, -0.28; NHAc, -0.29; I, -0.34; CHO, 6.34; NO2, 6.16; Br, 6.18; I, 6.22; COZH, 6.22; AcNH, -0.46; C02Me, -0.72; COZH, -0.80; NOz, -0.89. 6.24; Ph, 6.37; H, 6.34. 26. Jl3C.F. 2-Substituted fluorobenzenes (neat or CClr, 25'):q 12. ~ H O . 5-Substituted benzo[b]thiophenes (cDC13):* NHz, NH2, 236.7; OH, 241.6; OMe, 246.2; F, 254.5; CHO, 0.60; OH, 0.43; OMe, 0.35; Me, 0.31; OAc, 0.31; 11, 0; 256.4. OS02Me,e 0.08; C1, 0.07; CHZOH, 0.08; CHZC1, -0.01; 27. f16cl. 2-Substituted chlorobenzenes (77°K):~ NOZ, 37.260; Br, -0.06; CN, -0.18; NHAc, 0.02; I, -0.25; CHO, C1, 35.755; COZH, 36.305; NHAc, 35.150; CN, 35.500. -0.51; C02Me, -0.66; COZH, -0.73; NOZ, -0.84. H. Spiesecke and W. G. Schneider, J . Chem. Phys., a Reference 8. * N . Van Meurs, Recl. Trav. Chim. Pays-Bas., 87, 143 (1968). Reference 16 and K. Hayamizu and 0. Yamamoto, J . Mol. Spectrosc., 28, 89 (1968). e This value was not included 35, 731 (1961). M . Suzuki, Chem. Pharm. Bull., 16, 1193 (1968). 0 Y. Sasaki, M. Suzuki, T. in the correlation as constants for it are unknown. Hibino, K. Karai, M. Ilatanaka, arid I. Shiraishi, ibid., 16, 1367 (1968). ' I B. Caddy, M. Martin-Smith, It. K. Norris, S. T. Reid, and S. Sternhell, Aust. J . Chem., 21, 1853 (1968). Reference 14. 7 P. Diehl and G. Svegliado, Helu. Chim. Acta, 46, 461 (1963). k N. Nakagawa and S. Fujiwara, Hull. Chem. SOC.Jap., 34,143 (1961). Reference 10. m Reference 11. Reference 12. 0 Reference 13. Reference 7. q S. Mohanty and P. Venkateswarlu, Mol. Phys., 12, 277 (1967). p C. Heathcock, Can. J . Chem., 40, 1865 (1962).
evidence may be obtained from the confidence level of fi, the coefficient of the van der Waals radius term in eq 4. This confidence level is obtained by means of a "Student's t test" for the significance of fi. When the confidence level of fi is 290.0, the steric effect term is considered significant. A lack of correlation with eq 4 coupled with a lack of correlation by eq 2 does not imply case 2 . It may also be the result of case 1 due to faulty choice of the steric parameter. Correlation by eq 2 implies the existence of either case 3 or case 4, as, if steric effects are present and unaccounted for, no correlation with eq 2 is to be expected. Case 3 may be distinguished from case 4 by a comparison of hobsd (the
value for the unsubstituted compound) with hcalcdfrom the correlation. When hobad # hoalcd
(8 )
case 3 occurs, whereas when hobsd =
hoslcd
case 4 results. The data have been correlated with eq 2 and 4 by means of multiple linear regression ana1y~is.l~ The data used in the correlation are set forth in Table I. (17) I
