摘要:

40 J. Chem. SOC. (B), 1966 Molecular Polarisability. The Anisotropies of Carbon-Halogen Bonds in lsopropyl Halides By C.-Y. Chen and R. J. W. Le FBvre Apparent anisotropic polarisabilities for the three carbon- halogen bonds involved in isopropyl halides are deduced from relevant observational data. REFERENCES were recently made to unpublished measurements of the molar Kerr constants of isopropyl chloride, bromide, and iodide. We here record relevant observational details and deduce the apparent anisotropic polarisabilities of the three carbon-halogen bonds in- volved. EXPERIMEXTAL The isopropyl halides were prepared as directed by Vogel.2 Apparatus and procedures have been de~cribed.~ Measurements and results are set out in Tables 1 and 2 R. J. W. Le FCvre and B. J. Orr, J .Chem. SOC., (a) 1965, A. I. Vogel, ‘‘ Practical Organic Chemistry,” Longmans, 5349 ; ( b ) preceding Paper. London, 3rd edn., 1959, pp. 276, 280. under standard headings; equations used in deriving Table 2 from Table 1 were summarised in ref. 4. DISCUSSIOK The C-C-C and C-C-X angles in isopropyl chloride and bromide are tetrahedral; ref. 6 does not include data for the iodide. Assuming that (a) the three halides are similarly constructed, (b) the molecular resultant dipole moment p in each acts along the C-X line, (c) the longitudinal. transverse, and “ vertical I’ polaris- 3 C. G. Le Fkvre and R. J. W. Le Fhvre, (a) Rev. Pure AppZ. Chem., 1955, 5, 261; (b) Ch. XXXVI in “ Physical Methods of Organic Chemistry,” ed. Weissberger, Interscience, New York, 3rd edn., 1960, vol.1, p. 2459; (c) Chem. and Ind., 1955, 1121. 4 R. J. W. Le Fevre and K. M. S. Sundaram, J . Chem. SOL, 1962, 1494.Phys. Org. TABLE 1 Incremental * refractive indices, densities, dielectric con- stants, and Kerr effects observed for solutions in carbon tetrachloride containing weight fractions wp of solute at 25' lO5wz 672 1046 1294 1930 2246 3227 3431 589 731 1064 1507 1654 2492 105w, ...... 10"AB ... - 1 0 4 ~ n - 1 0 4 ~ d 1 0 4 ~ & Solute : isopropyl chloride 699 17 1340 1027 21 1700 1286 30 2490 1918 - - 2228 47 4140 3108 51 4400 3337 - - Solzrte : isopropyl bromide - 180 388 1 230 480 2 340 715 3 470 1036 3 510 1119 - - 1681 Solute : isopropyl iodide 897 1241 1638 2238 776 1021 1331 1903 1 O1'AB 562 888 1147 1644 1855 2754 2979 543 678 976 1375 1509 2200 2848 2500 * When wz = 0, n = 1.4575, d = 1.58454, E = 2.2270, and B = 0.070 x lo-'.TABLE 2 Polarisations, molar Kerr constants, etc. PrC1 ............ 9.824 -0.8126 -0.098 122-0 PriBr ............ 6-743 -0-1969 -0.011 129-4 PrfI * ............ 5.402 +0.0670 +Om026 121.4 Solute EEl B Y 6 Solute 1012m(mKz) WP, (c.c.) BD (c.c.) p (D) t PriC1 ...... 70.23 107.85 20-74 2.05 PriBr ...... 118.3 114.86 24.70 2.08 PriI * ...... 143.5 11 8.00 28-30 2-08 1-05 RD. * Polarisation data from ref. 5 . t Calculated taking =P abilities * of C-C are @99,0.27 , and 0.27, re~pectively,~~~ (d) the C-H bond is isotropically polarisable 3c with bi = 0.64, and (e) the (deformation polarisation) /(electronic polarisation) quotients are 1.1 , then the equation given on p.55 of ref. 7b can (after insertion of the trigonometrical functions for 109" 28' and numerical values of the various constants involved) be rewritten for 25" as: where 8, and 0, are the " anisotropy " and " dipole " terms contributing to a molar Kerr con~tant,~a.~a and D is (bL - bT) for C-X in Me,CHX. Equation (1) and observed values of (mK2) are connected by equation 1037(e, + e,) = 23m,(,~,) (2) (2) : * Principal molecular polarisabilities bi (i = 1, 2, or 3) and principal bond polarisabilities bi (j = L, T, or V) are expressed in cubic Angstrom units unless otherwise stated. A. Audsley and F. R. Goss, J. Chem. SOC., 1942, 358. 8 L. E. Sutton, " Tables of Interatomic Distances and Con- figuration in Molecules and Ions," Chem. SOC. Special Publ. No. 11, 1958.41 The measurements of Table 2 yield, through equation (2) then (l), solutions for D as in Table 3. To place estimates of bond polarisabilities on a consistent basis, the sums Zbj = bJ;(CX) + bT(CX) + bV(CX) are evaluated from the electronic polarisation listed by Le Fcvre and Steel,* and the individual values of bL and bT computed accordingly. The longitudinal polarisabilities so found are close to those deduced previously for C-X in ethyl halides (viz., 3.6 for C-C1,lb 5-3 for C-BrJg and 7.6-8-0 for C-I la) and lie between others extracted TABLE 3 Estimates of bL and bT for C-X in isopropyl halides D Cbj bL(CX) bl.(CX) = b,(CX) 1-87 C-Cl ... 1-96, C-Br ... 2.89, 10.77, 5-53 2.63 7-56, 3.83 C-I . . . . . . 3-39, 16.55, 7.78 4.39 earlier from the corresponding methyl and t-butyl halides.Because the last-named molecules have rotational symmetry, with their C-X axes and resultant moment directions coincident, value of bL(CX) can be drawn from them more confidently than from the ethyl or isopropyl halides. We have therefore sought for possible formuk whereby a bI,(CX) in RCH,X or R,CHX might TABLE 4 Empirical connections between V C - ~ and Q Halide 1024bL(CX) Y (A) 103Q v (cm.-1) MeCl ......... 3-18 1.784 103.2 732 MeBr ......... 4-65 1.939 94.28 610 Me1 . . . . . . . . . . . . 6-70 3.139 86.07 525 Me,CCl ......... 3.94 1.765 113-3 568 Me,CBr ...... 5-86 1.92 103-9 515 Me,CI ......... 9.19 2-15 94.64 487 Interpolation formulz between MeX and Me,CX (a) Between MeCl and Me,CCl: v = 2408 - 16,237Q. (b) Between MeBr and Me,CBr: v = 1545-991712.(c) Between Me1 and Me,CI: v = 907 - 4434Q. TABLE 5 Applications of interpolation equations of Table 4 Other Halide v (crn.-l) lOaQ Y (A) 1OZ4b~(CX) estimates EtCl 656 107.9 1.77 & 0.01 3.47 f 0.12 3.6 (ref. l b ) PriC1 612 110.6 1.76 5 0-02 3-61 f 0.25 3.83 (Table 3) EtBr 560 99.32 1-91 f 0.02 4.97 f 0.31 5-3 (ref. 9) PriBr 536 101.7 1-91 f 0.03 5.34 0.51 5.52 (Table 3) EtI 500 91.79 2-18 f 0-05 9-1 & 1.3 7.6-8.0 (ref. 8 PriI 489 94.27 (2.18 f 0.05) (9.9 f 1.3) 7.78 (Table 3) 1 4 be predictable by interpolation from the extreme values afforded by MeX and Me3CX. Most promise is shown when bond-stretching frequencies (v, in cm.-l) are con- nected with the quantities Q = (l/r2) (b~/i1?)'!~, where, for a given bond, I is the inter-centre distance (in A), 7 R. J. W. Le Fbvre, (a) J . Proc. Roy. SOC. New South Wales, 1961, 95, 1; (b) Ado. Phys. Org. Chern., 1965, 3, 1 ; (c) Proc. Chem. SOC., 1959, 363. 8 R. J. W. Le Fbvre and K. D. Steel, Cltem. and Ind., 1961, 670. B C. G. Le Fkvre, R. J. W. Le Fbvre, and A. J. Williams, J. Cham. SOC., 1965, 4188.42 J. Chem. SOC. (B), 1966 bL the longitudinal polarisability (in 10-23 C.C. units), and= the reduced r n a ~ s . ~ ~ In Table 4 data are assembled for bL(CX) (from refs. la, l b , 7b, and 9), Y C - ~ (from ref. 6), and v ~ - ~ (from ref. 10) ; three empirical equations (a), ( b ) , and (c), appropriate, respectively, to the chloro-, AUSTRALIA. [5/866 Received, August 10112, 1965.1 PriI is not given in ref. 6; 2.18 0.05 is taken from EtI ; if rc-I in Pr'I were as short as 2.095 A then b~(C-1) would emerge as 7.77. UNIVERSITY OF SYDNEY, N.s.w.,

ISSN:0045-6470    

DOI:10.1039/J29660000040

出版商:RSC    

年代:1966

数据来源: RSC