GROUPELECTRONEGATIVITY AND POLAR SUBSTITUENT CONSTANTS
APRIL1967
1161
Group Electronegativity and Polar Substituent Constants NI. A. DAVIS* Divi&m of Chemistry, Worcester Polytechnic Institute, Worcester, Massachusetts Received October 8,1964 The relationship between polar substituent constants ( u * ) and group electronegativity values ( X ) calculated 2.06 by the method of phosphoryl absorption frequencies has been examined. The relations X = 0.370* and X = 0 . 2 6 ~ * 2.30; T = 0.88 were obtained. From these relationships, the group electronegativity of 44 organic groups was calculated and compared with values obtained by various other methods wherever possible.
+
+
It was originally felt that electronegativity was a fixed property of atoms.2 However, several workers have recently suggested that the electronegativity of an atom is not invariant but depends upon its environment in a m ~ l e c u l e . ~ -Clifford ~ has shown that group electronegativity values may be obtained by simply averaging the individual electronegativity values of the atoms comprising the group.8 It has long been postulated that the Taft u* values are a function of electronegati~ity.~Jaff6, et. al., obtained one relationship for various fluorinated methyls, and a.nother relationship for various chlorinated methyls, but neither hydrogen nor the monobromo- or monoiodomethyls fell on either of these two Other values of group electronegativity have been obtained empirically from infrared,’O solubility,B basicity and coupling potentia1,l’ and nmr data,’? but no relationship between these values and U* has been established. Recently,13 Huheey has presented a method for calculating group electronegativity by assuming variable electronegativity of the central atom in the group and equalization of electronegativity in all bonds. l5 This method of electronegativity equalization has most recently led to an equation relating u* and the charge (6) induced on the carbethoxy group as calculated from group e1e~tronegativity.l~This manuscript also presents a general empirical relationship between group electronegativity (X) obtained from phosphoryl absorption frequencies, and polar substituent constants (.*)* Methods.-The electronegativities of various substituent groups were obtained by substituting the (1) To whom correspondence should be addressed: Harvard University, School of Public Health, 55 Shattuck St., Boston, Mass. (2) L. Pauling and D. M . Yost, Proc. Natl. Acad. Sci. U. S., 14, 414 (1932); L. Pauling, “The Nature of the Chemical Bond.” 3rd ed, Cornell University Press, Ithaca, N. Y., 1960. (3) A. D. Walsh, Discussions Faraday Soc., 2, 18 (1947). (4) R. T. Sanderson, J . Chem. Educ., 81, 2 (1945); “Chemical Periodicity,” Reinhold Publishing Corp., New York, N. Y., 1960. ( 5 ) H. 0. Pritchard and F. H. Sumner, Proc. R o y . Soc. (London), AP85, 136 (1956). (6) R. P. Iczkoivski and J. L. hfargrave, J . A m . Chem. Soc., 88, 3547 (1961). (7) (a) J. Hinze and H. H. JaffB, ibid., 84, 540 (1962); (b) J. Hinze, M. A. Whitehead, and H. €1. Jaff6, ibid., 86, 148 (1963); (0) J. Hinze and H. H. Jaff6, J. Phys. Chem., 67, 1501 (1963). ( 8 ) A. F. Clifford, ibid., 68, 1227 (1959). (9) R. U’.Taft, Jr., J . A m . Chem. Soc., 7 4 , 2729, 3120 (1952). {IO) (a) R. E. Kagarise, ibid., 77, 1377 (1955); (b) J. V. Bell, J. Heisler, H. Tannenbaum, and J. Goldenson, ibid., 76, 5185 (1954); (c) J. K. Wilmshurst, J . Chem. Phys., 28, 733 (1958). and earlier papers; (d) E. A. Robinson, Can. J. Chem., 89, 247 (1961). (11) D. H. RlcDaniel and A. Yingst, J. A m . Chem. Soc., 86, 1334 (1964). (12) B. P. Dailey and H. N. Shoolery, ibid., 77, 3977 (1955).
(13) It should be noted that this paper was first submitted for publication before the work of Hiibeey appeared in print.1‘ (14) J. E. Huheey, J . Org. Chem., 81, 2365 (1966). (15) (a) J. E. Huheey, J. Phys. Chern., 68,3073 (1964); (b) ibid., 68, 3284 (1965); ( c ) ibid., 70, PO86 (1966).
3.
2.!
xeq 1
2.0
1.5 0
1
G*
Figure 1.- Plot of
X., 1 vs.
i u*.
2.0 -.
1.5 0
Figure 2.-Plot
1
2
G* of X,, us. u*.
phosphoryl-stretching frequencies obtained by Griffin’6 into both the Bell equation (eq 1) and the Robinson equation (eq 2) relating Z X with phosphoryl absorption frequencies.1°b,d (16) C. E. Griffin, Chem. Ind. (London), 1058 (1960).
1162
DAVIS
VOL.32
TABLE I
X ( p ) = (39.96
- ZX)/3.995
(1)
CALCULATION OF GROUP ELECTRONEGATIVITY (XI FROX EQ1 AND EQ2 R
CHI CzHb n-C8H, n-C4H3 CHz=CH CHz=CHCHz Cs&CHz CsHs CHzC1 CHClz
cc13
CHZBr CHaC(0)CHz
X (cm-1)
X (p)
8.05 8.03 8.06 8.06 8.10 7.98 8.04 7.96 7.90 7.83 7.83 7.88 i.96
1242 1245 1241 1241 1234 1253 1244 1256 1266 1274 1277 1269 1256
o*
0.00 -0.10 -0.11 -0.13 0.40 0.13 0.21 0.60 1.05 1.94 2.65 1.00 0.60
Xes I
Xeq
2.00 2.08 1.96 1.96 1.80 2.28 2.04 2.36 2.60 2.80 2.88 2.68 2.36
2.27 2.32 2.24 2.24 2.13 2.46 2.30 2.52 2.70 2.84 2.89 2.75 2.52
I
The compounds used were diethylalkyl or -aryl phosphonates of the type (CzH50)2P(0)R.Once ZX is obtained it is a simple matter to subtract the electronegativity due to the two ethoxy groups, thus leaving the electronegativity of the R group ( X ) . The ethoxy group was assigned an electronegativity of 2.90, so that Z X - 5.80 = X . The results along with the corresponding phosphoryl-absorption frequencies and B* values are shown in Table I .' (17) R. W. Taft, Jr., "Steric Effects in Organic Chemistry," M. S. Newman, Ed., John Wiley and Sons, Inc., New York, N. Y., 1966.
TABLE I1 COMPARISON OF CALCULATED AND LITERATURE ELECTRONEGATIVITY VALUES NO.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Group
FzCH CH30C(O) (CH3)3N+CHz CHsC(0) CH30 0zNCH2 CzHj0 CsHjCEC CH3S(02)CHz NCCHz FCHz HOC(0)CHz CF3CHg ICHZ CsHsOCHz CsHiC ( 0 H ) H C?HsOC(O)CHz (CH3)zN HOCHz CHsOCHz OzXCHzCH2 H CsH,CH=CH (CsHj)zCH ClCHzCH? CH,CH=CH C F3 CH 2 CH z CH3CH=CHCHz CFaCHzCHzCHz CsHjC(CH3)H CsHjCH?CHz CBHBC(CBHB)H CsHjCHzCHzCHz C-C~HIICHZ i-CaI19 C-CBHI~ (CH3)3CCHz i-C3H7 c-CsHo sec-C4H3 (CzHj)?CH (CH3)aSiCHZ (CH3)aC(CHa)CH t-CaHg
U*
Xes 1
Xeq :
XH"
Xother
2.05 2.00 1.90 1.65 1.46 1.40 1.35 1.35 1.32 1.30 1.10 1.05 0.92 0.85 0.85 0.76 0.71 0.65 0.55 0.54 0.50 0.49 0.41 0.40 0.38 0.36 0.32 0.13 0.12 0.11 0.08 0.04 0.02 -0.06 -0.12 -0.15 -0.16 -0.19 -0.20 -0.21 -0.22 -0.26 -0.28 -0.30
2.82 2.80 2.76 2.67 2.60 2.58 2.56 2.56 2.55 2.54 2.47 2.45 2.40 2.38 2.37 2.34 2.32 2.30 2.26 2.25 2.24 2.24 2.21 2.21 2.20 2.19 2.18 2.11 2.10 2.10 2.09 2.07 2.06 2.04 2.01 2.00 2.00 I .99 1.99 1.98 1.98 1.96 1.96 1.95
2.84 2.82 2.79 2.73 2.68 2.66 2.65 2.65 2.64 2.64 2.59 2.57 2.54 2.52 2.52 2.50 2.48 2.47 2.44 2.44 2.43 2.43 2.41 2.40 2.40 2.39 2.38 2.33 2.33 2.33 2.32 2.31 2.30 2.28 2.27 2.26 2.26 2.25 2.25 2.25 2.24 2.23 2.23 2.22
3.00 2.94 2.62 2.69 2.68
2.81,b 2.94,b 3.12c 2. 54d 2. 5gd 2.48," 2.52,c 2.83d
2.53 2.61 2.86 2.96 2.61 2.98 2.90 2.37 2.58 2.59
2.41,c2.44,c 2.83d
2.40 2.74 2.52 3.07 2.20 2.48 2.48 2.49 2.37 2.70 2.45 2.60 2.42 2.42 2.40 2.40 2.29 2.29 2.29 2.29 2.28 2.29 2.29 2.29 2.33 2.29 2.29
2. 37,c 3 . OOd 2.08,d 2.52c
2.39,b 2.61,b2.70" 2. 36,b 3 . O l e 2. 2. 36,c 2 . 3gb
2.205
2.07b
2. 60d 2.29c
2.29O
4 Calculated inherent electronegativity (a) in Pauling units.16 * Calculated by Jaff6.' Calculated by the method of Clifford*using electronegativity values of Jaff6.7 Calculated by the method of Bell.lob e Calculated by the method of S a n d e r ~ o n . ~
APRIL1967
REDUCTION OF METHYL VIOLOGEN Results and Discussion
The least-squares linear regression equations of X
w.u*, as shown in Figures 1 and 2, gave eq 3 and 4. Xeq
1
X,.,?
=
0 . 3 7 ~ * 2.06
+
(3)
+ 2.30
(4 )
0.26a*
The standard deviation from regression (Sx..*) was 0.17 for eq 3 and 0.12 for eq 4. The Student “t” test gave t = 6.18 and 6.24, respectively, both of which have p > IC-1 and less than kz, kg, and k4
