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COMMUNICATIONS TO THE EDITOR
the metal concentration, and since the equation5 used involves the refractive index of the solid salt and complex polarizability of the electron in a solid, we can only estimate that the oscillator strength is less for the molten system than for the solid. This can be interpreted as indicating an interaction of the electron with the ions surrounding it. ( 5 ) F. Seitz, “ M o d e r n Theory of Solids,” McGraw-Hill Book Co., Inc., New York. N . Y., 1940, p . 66.5
Vol 86 TABLEI
JI~CC of C (CHo)sC13C H Compounds Compound
J‘VCCH
( CH3)3C13CH20H ( CH3)aC’3CHz0COCsHaOCH3(p) ( CHa)aCl3CHzOCOC6H~ ( CH3)aC13CH~OCOCaHiNOz( 9) ( CH3)aC13CH2C1 ( CH3)3Cl3CH2Br
4 4 4 4
48 74 81 91 5 63 5 84
5 99
(CHi)aC’3CHzI J . GREENBERG ( CHa)3C13C(CH3)=CHz I. WARSHAWSKY ( CH3)3CL3C( CH3)-0 ( CHa)3Ci3COzH ( CH3)3Cl3CO2C6H4OCH3(p) RECEIVED MARCH5, 1964 (C H I ) ~ C ’ ~ C O ~ C S H ~ ( CHa)3C13C0zCsHaN0z( p) ( CH3)3CI3COCI Proton- 13CSpin-Spin Coupling. V. Inadequacy of (C H ~ ) Z C ~ ~ C O B ~ Correlation of Proton- I3C Coupling with +Character ( CH3)aCl3C=S
LEWISRESEARCH CENTER NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND, OHIO
Sir: The short-range proton- 13C coupling, JHCH, has been extensively investigated. The general linearity between JUCH and fractional s-character of the I3C hybrid atomic orbital has led to the conclusion that the contact term is essentially the sole contributor to the coupling. Additivity relations, with some exceptions, l e of substituent effects on J i Z c H in substituted methanes“ and formyl compoundslg have been discovered. For the former compounds this additivity has been derived and interpreted from valence bond theory.lh On the assumption therefore that the contact term is essentially the sole contributor to the coupling, fractional s-characters have been calculated, usually in three significant figures, from experimental JI~C values. H Long-range proton- 13C coupling has en joyed less attention than J ~ ~ c H .From the approximate linearity between J ~ ~ c C and H fractional s-character of the I3C hybrid atomic orbital, it was concluded2 that the contact term dominates this coupling when the 13CCH angle is tetrahedral. No such obvious correlation was found3 in J t 3 C c C H . We shall present data that focus attention on the inadequacy of correlation of proton-’3C coupling with s-character. Three-Bond Coupling.-Table I summarizes J13CCCH values, accurate to *0.05 c.P.s., for a few selected (CH3)3C!l3C compounds. The failure of a single factor4 to accommodate the data is obvious. The most striking and pertinent observations are: unusually high values for the halogen compounds; increase of these values in the order chloro < bromo < iodo, whereas from halogen electronegativities the reverse order is expected (see para-substituted neopentyl benzoates and phenyl pivalates) ; and greater (1) ( a ) P. C . I.auterbur, J Chem P h y s , 2 6 , 2 1 7 ( 1 9 5 7 ) , J A m Chem SOC, 83, 1888, 1816 (1961), (b) J N . Shoolery. J Chein P h y r , 31, 1427 ( I U S , (c) N. Muller a n d I ) . R . Pritchnrd, ibid., 31, 768, 1171 (19.59), ( d ) N. Muller, ibrd., 36, 359 ( I R 6 2 ) . (e) N. M u l l e r a n d P I . Rose. J A m . Chrm. Soc , 84, :3973 ( 1 0 6 2 ) . ( f ) E . R . Malinowski. ibid , 83, 3479 (1961). (g) E. K . Malinowski. 1. Z Pollara. a n d J . P L a r m a n n , :brd , 84, 2648 ( l 9 6 2 ) , (h) H . S G u t o w s k y a n d C . S . J u a n , : b i d , 84. 307 ( I Y C Z ) , . I . Chpm P h y s . , 37, 2198 ( I M Z ) , ( j ) H . Ilreeskamp and K S a c k m a n n . L P h y i r k C h c m , ( F r a n k f u r t ) , 34, 273 (1962) ( 2 ) G J K a r a b a t s o s , J . 1) G r a h a m , a n d F. A I . Vane. J P h 3 s Chem , 6 6 , 1657 (1861) ( 3 ) G J. K a r a b a t s o s , J I ) . G r a h a m , a n d F. ?VI V a n e . J A m [ h e m . S o < , 8 3 , 2778 (1961). ibid., 84, 37 (19621. (4) I)etailed di-cusiion of each contributing factor, F e , substituent elec t r < , n r y a t i \ i t y , a n g l e deformations. hybridization. etc , w i l l h e given later
00 20 38 58 60 76 5 99 6 43 5 38 4 4 4 4 4 4
variation of the values for the halogen compounds when the is sp2 rather than sp3 hybridized. These results could be interpreted in terms of spin-dipole and/or electron-orbital contributions to the coupling (interactions between the proton magnetic moment and currents induced on the halogen by the I3C nucleus), since such contributions should be significant when the substituent has anglular-dependent atomic orbitals (p, d, f ) ; and increase i n the order chloro < bromo < iodo. Two-Bond Coupling.-The magnitude of J I ~ Cfor CH acetyl halides (Table 11) is also consistent with possible TABLEI1 J I ~ C of C CHaF I 13C Compounds Cornpound
J(?(.cH
CH313C[(CHa)3C]=CH2 B (CH3)zL3C=0 5 CH1’3C0zH 6 CH3L3CO?C6HaOCHoIp)7 CH313C0?CsHj 7
40 90 80 00
0.1
Compound
JIPCCH
CH>’3C0zCsH~N02(~ 7 ) 16 CHsl’COSHz 6.01 CHx”COC1 7 58 CHJ13COBr 7 BO CH3I3COI 7 30
spin-dipole and/or electron-orbital contributions to the two-bond coupling. One-Bond Coupling.--If the spin-dipole and/or electron-orbital terms contribute to long-range proton13C coupling, it is only reasonable to expect that they may contribute to J b l C ~ . The following could be interpreted in such terms. (a) Increase in the electronegativity of the group attached to the should increase J j 3 c H ; e.g., for t ~ e o p e n t y l - l - ~benzoates ~C as the para substituent changes from methoxy to hydrogen to nitro, J I T C H changes from 145.7 to 146.1 to 146.8 c.P.s.,yet for the n e ~ p e n t y l - l - ’ ~halides C J‘CH changes from 147.8 (chloro) to 149.1 (bromo) to 148.0 c.p.s. (iodo). Xlethyl halides show the same trend‘: 150 (chloro), 152 (bromo), 151 C.P.S. ( i ~ d o ) .(b) ~ If values are unusually the I3C is sp2 hybridized, J,$cH high when a halogen or oxygen is bonded to i t ; e.g., for formyl fluorideld and methyl formate,Id J:CH values are 2G7 and 226 c.p.s. respectively. That the effect may be detectable even when the halogen is not directly bonded to the ‘“Cis shown by the higher .TI,CI< values of ortho-substituted benzzldehydes when the orfho substituent is a group with angular-dependent atoniic orbitals; e.g,, .IiicH (c.p.s.) = 174 (benzaldrhyde), 173.3 (%methyl), 174 (:3-methyl), liiL5 (4f.i)Thrs ; i n o m a l y has 1,een i n t e r p r e t e d p > e \ ~ o u s l y(ref l c l incrva5ps i n Q( as t h e c X intriati,rnic dmtanc? inal-ea-es
IU
tv1111.
Sept. 5, 1964
COMMUNICATIONS TO THE EDITOR
3575
methyl), 182 (2-fluoro), 178 (3-flUorO), 175.5 (4-fluoro), wise interactions. For simplicity, we will redefine the 0.5({, Cy), 182.5 (2-bromo), 177.5 (3-bromo), 180 (2-methoxyl), interaction parameter by vxy = so that the equation above becomes J(xyz) = vxy 175.5 (3-methoxy), and 173 (4-methoxy). (c) In system I, when X = C ~ H SJ ,~ ~ c H A= 156 and J U C=H ~ q x z vyz, where J(xyz) is a coupling constant for a 162 c.P.s.; when x = c1, J L a C H A = 160 and J L ~ C H B= compound containing substituents x, y ) and z. The parameters shown in Tables I and I1 have been evalu-
rXy+
+
+
+
TABLE I INTERACTION PARAMETERS, vxx, FOR JCF AND J B ~ A , CALCULATED BY n,, = J(xxx)/3
1
161 C . P . S . ~ When x = Br, J I ~ C =H 163.8 ~ and J i a C H B Interaction 1gC-F 1gSi-H = 159.6 c.P.s.' This change in the J ~ ~ C H Aratio / J I ~ C H Bparameter couplings, C.P.S. couplings.d C.P.S. from styrene to vinyl bromide is also consistent with H,H 52.6" 6i.5 contributions from the spin-dipole and/or electronF,F 86.0" 127.2 CI,Cl 112.2b 121.0 orbital terms8 Br,Br 124.Oc 107 9 On the basis of these arguments, i t is evident that sCalculated from an average of values found by N. Muller and characters calculated from JllCH are unreliable and misD . J. Carr, J. Phys. Chem., 67, 112 (1963). and in ref. 5. b Calculeading. Values calculated from the long-range coulated from an average of values found by Muller and C a w and pling are meaningless even when expressed in one sigin ref. 7. Calculated from an average of values found by R. K . nificant figure ; those calculated from the short-range Harris, J . Mol. Spectry., 10, 309 (1963). and by P. C. Lauterbur in "Determinations of Organic Structures by Physical Methods," coupling are probably equally meaningless whenever Vol. 2, edited by F. C. Nachod and W. D. Phillips, Academic two or more heteroatoms are bonded to the I3C. Data taken from Press, Inc., New York, N. Y., 1962, p. 505. Acknowledgment.--U'e thank the United States ref. 8. Atomic Energy Commission for financial support TABLE I1 (Grant CCO-1189-11). (6) E. B. Whipple, W. E. Stewart, G . S. Reddy, and J. H. Goldstein, J Chem. P h y s . , 34, 2136 (1961). ( i )R . M. Lynden-Bell, M o l . P h y s . , 6, 537 (1963). (8) T h e validity of our suggestion t h a t spin-dipole and electron-orbital terms contribute to proton-lgC coupling certainly requires further experimental scrutiny, in view of theoretical predictions by J. A. Pople, ibid., 1, 216 (1958) t h a t "coupling via currents induced on a third a t o m will always be negligible." (9) Fellow of t h e Alfred P . Sloan Foundation. (10) National Science Foundation Predoctoral Cooperative Fellow, 1962-
INTERACTION PARAMETERS, q x y , FOR J C FA N D J S , ~ , CALCULATED B Y vxXy= [J(xxy) - n,,] /2 Interaction parameters
lac-F couplings. C.P.S.
ZqSi-H couplings,e C.P.S.
C1,H 90.8" 83.5 F,H 93.6' 77.4 F,Br 119.0" F,C1 106.5" F,CX 8 9 .O d 1964. H,CN 59.7d KEDZIECHEMICAL LABORATORY GERASIMOS J . KARABATSOS~ Data taken from G . V. D. Tiers, J . A m . Chem. SOC.,84, MICHIGAN STATE UNIVERSITY CHESTER E. ORZECH, JR. lo 3972 (1962). Calculated from a n average of values found by EASTLANSING, MICHIGAN Muller and Carr, footnote a, Table I, and in ref. 5 . data RECEIVED APRIL27, 1964 taken from Muller and Carr, footnote a, Table I. Data taken from ref. 3. e Data taken from ref. 8.
Substituent Effects. 111.' Correlation of IaC-F and *$Si-H Couplings by Pairwise Interactions
Sir :
ated in a straightforward manner; namely, vxx = J(xxx)/S and q x y = [J(xxy) - qXx]/2, respectively. A comparison between observed and predicted coupling constants is shown in Table 111. Consider-
A "direct" additivity rule for J C H for substituted TABLEI11 methanes of the type CHXYZ was first observed by COMPARISON BETWEEN CALCULATED A N D OBSERVED = by lz, where Malinowskiz; namely, JCH COUPLING CONSTANTS lx is a parameter associated with substituent x. SigCompound Jealcd. C . P . S . Jo,,*d, c p.5. 1)ifferencp nificant departures from this simple additivity rule calcd. have been r e p ~ r t e d ~for - ~ compounds which contain obsd , c.p.s. highly electronegative substituents. Recently, DougJR>-H lasG introduced pairwise interaction terms as correcSiHsCl 7JH.H + 27JCI.H 234 5 238 1" +:3 6 tions for departures from "direct" additivity. EssenSiHzF ?H.H + + F . H = 222 3 22Y 0" +6 7 lY tially, his equation can be written as J C H = { x Jc-F (. fxy lXz lyZ, where is an interaction 7 H . H + 27JH.F = 239 i CHiFi 233 J h +6 3 parameter associated with substituents x and y, and is CFzBrz ? B ~ . B+~ ~ ~ J F . B ~ = 362.0 357 8' +4 2 independent of substituent z. ~JCI.CI + ~ ? F . C I 325 2 CFlCh 324 i d +O 5 CFzHCN ? H . F + ~ H . C N+ ~ J F , C N = 242.3 243 S e -I 2 Recently it has been reported that J ~ F and~JS~H*.' . ~ a Data taken from ref. 8. b An average of values found by do not obey the "direct" additivity rule. We wish to Muller and Carr, footnote a , Table I , and in ref. 5. An average report here that J C Fand J s i ~ can be correlated by pairof value found by Muller and and by Harris, footnote c,
rx +
+
+
+
rxy
+
+ +
-
-
(1) P a r t I 1
J
E . R . Malinowski, L. Z Pollara, and J . P Larmann, A m C h e m . S O C .84, , 2649 (1962) ( 2 ) E R . Malinowski, ibid, 63, 4479 (1961). (3) G. P. van der Kelen and Z. Eeckhaut, J. .Ifoi. Specfry.. 10, 141 (1963) (4) N . Muller and P . I. Rose, J . A m C h e m . Soc , 84, 3973 (1962) ( 5 ) S. G Frankiss, J . P h y s C h e m . . 6 7 , 752 (1963). (6) A. W . Douglas, J C h e m . Phyr , 40, 2413 (1964) (7) R K Harris, J. P h y s . C h e m . , 6 6 , 768 (1962). (8) E. A V Ebsworth and J J Turner. J C h e m . P h y r , 36, 2628 (1962) (9) H . S. Gutowsky and C S J u a n , tbid , 37, 2198 (1962).
Table I. .4n average of values found by Muller and Carr,h and by Lauterbur, footnote c, Table I . e Data taken from ref. 3.
ing that the evaluation of the interaction parameters does not take into account the inherent error in the measured coupling constants, we conclude that the agreement between experiment and prediction is very good. Obviously a trial-and-error or a least-squares
