1,3,5,7,9,11,13,15,17,19-eicosadecaene [x;Ft
,,,e
tions to this behavior are the two -R substituents, OH and NH2, for which the m.c.p. can be influenced by hydrogen bonding between the substit(6) F Sondheimer, R \\-olovsky and D A. Ben-Efraim, t o be published uent and the hvdroxvlic solvents. Consistent with DANIELSIEFFRESEARCH INSTITUTEFRANZ SOSDHEIYER such an interpietati& are the facts that the m.c.p. OF SCIESCE REUVEN WOLOVSKY ~TEIZMANN INSTITUTE REHOVOTH, ISRAEL YEHIELGAOSI values for the proton donating OH group are more negative (greater electron density) and those RECEIVED DECEMBER 19, 1959 for the proton accepting NH2 group are less negative in hydroxylic than in the non-hydroxylic SOLVENT EFFECTS ON MESOMERIC CHARGE solvents. SEPARATION’ In contrast; the m.c.p.’s for every +R substituent Sir: show that the electron density a t the F19 atom is Reactivity2 and dipole moment3 data have sug- decreased appreciably with increased ability of the gested that the contribution to the resonance hy- solvent to support ionization. The nature of the brid of dipolar resonance structures, e.g. present results is such that these solvent effects must be ascribed to the increased contribution to the resonance hybrid of the dipolar resonance form6 is enhanced by solvents which support ionization. We report herein unequivocal evidence for such phenomena based upon the difference in the F19 + F o x ( n.m.r. shielding parameters for substituents in the I t is of interest to note in connection with the p - and m-positions of fluorobenzene, SPF - SmF. This quantity (hereafter referred to as the meso- nearly solvent independent character of the m.c.p.’s (principal bands) 376, 397, 420 and 447 mfi1.6
TABLEI MESOMERIC CIIARCE PERTURBATIONS ( M . C P.’s), SPF - SmF= H,F Suhst.
Class
Cyclo-CsHii
CCla
SHn OCHI
-R -R -R -R -R -R +R
-13.8 f 0 . 1 -12 6 f 0 . 1 -12.1 rt 0 . 1 - 9.8 0.1 - 0 0 i0 . 1 - 5 1 i0.1 (insol.) 5.8f 0.1 5 . 6 rt 0 . 1 j . 8 f0.1 7.8 f0.1
-13.8 f 0 2 -12.6 f 0 . 1 -12.2 i 0 . 1 - 9 8 f0.3 - 6 0 f0.1 - 5.1 + 0 . 1 (in sol, ) 6 . 1 i.0 . 1 5.9 f 0 . 1 5.8 f0.1 8.1 =t0 . 2
011
F OCOCHZ c1 COnH COzCrHj CHsCO NO2
CHO
+R +R +R +R
*
meric charge perturbation, m.c.p.) provides a quantitative measure of the order of electron densities in the immediate vicinity of the F19 nucleus produced by mesomeric interaction of the para substituent.2cf 4 Table I records m.c.p.’s for a variety of typical -R and +R substituents in four solvents a t “infinite dilution.” The m.c.p. values for most -R substituents show a second order dependence on solvent which cannot with confidence be taken to appreciably exceed the limits of the present experimental error. Apparently the average m.c.p.’s listed for these substituents are therefore approximate intramolecular properties. The only excep(1) This work was supported in part by t h e Office of Naval Research, Project NR055-328. (2) (a) B. Gutbezahl and E. Grunwald, THIS J O U R N A L , 76, 559 (1953); (b) XI. M. Davis and H. B. Hetzer, J . Res. N n l . Bur. Stand., 6 0 , 569 (195.3); (c) R. W. Taft, Jr., S. Elireuson, 1. C. Lewis and R . E. Glick, THISJ O U R N A L , 81, 5352 (1959). (3) J. W. Smith, J. Chem. Soc., 109 (1953). (4) H. S. Gutowsky. D. W. McCall, B. R . McGanrey and L. H. hieyer. THISIOURNAI. 74. 4809 (1932).
-
HPF(IN P.P.hZ ), FOR SCBSTITUTED FLUOROBENZEVES Solvent Av. CHaOM 75% a q CHaOH
-13.4 f 0 . 1 -12.6 f 0 . 2 -13.5 zk 0 . 2 - 9.7 f 0 , l - 5 . 8 f0 . 1 - 5.1 & 0.1 6.4 f0.1 6 . 5 zt 0 . 1 6.6 f0.1 G . 5 rt 0 . 1
...
-12 9 f 0 1 -12 5 f 0 1 -13 0 f 0 2 - 9 5 f O O - 5 i r t O l -49 1 01 6 6 f 0 1 66f01 7 3 f 0 1 7 2 f O 1 9 0 1 0 1
... -12.6
...
-
9.7 - 5.9 - 5.1
...
...
for the -R substituents that the contribution to the resonance hybrid of the dipolar canonical form +
X -O
F
is apparently much less dependent upon solvent than that of the above type.2C Solutions 5% (by vol.) in the substituted fluorobenzene were employed and the shifts obtainedzc relative to the internal standard (2%) tetrafluorotetrachlorocyclobutane.6 We are much indebted to Dr. G. V. D. Tiers for suggesting and supplying a sample of this standard. ( 5 ) R. W. Taft, Jr., t b i d , 79, 1045 (1957). (6) G. V. D. Tiers, J . Phys C h e m . , 63,761 (1959).
ROBERT W. TAFT,JR COLLEGE OF RICHARD E. GLICK CHEMISTRY AND PHYSICS THE P E N N S ~ V A N I A IRWINC. LEWIS STATEUNIVERSITY IRWINFox STANTON EHRENSON UKIVERSITY PARK,PA. RECEIVED NOVEMBER 23, 1959
