The dipole moments of six ethyl substituted benzenes were determined in dilute solution in benzene. The effects of methyl and ethyl groups on other substituent in the benzene ring have been discussed in the light of the observed moments

Murty, C R K

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DIPOLE MOMENTS OF SOME SUBSTITUTED BENZENES AND PYRIDINES. PART III. CHLORO-AND BROMO ETHYL BENZENESC. R. K. MURTYPhysics Depahtmbnt, Andhra University, Waltair [Received for puhlicaiion, May 27, 1968)A B ST R A C T . The dipole moments of six ethyl substituted bonzonoe were dotorminod in  dilute solution in benzene. The effects of methyl and ethyl groups on other jsiibstituents in  the benzene ring have been discussed in the light of the observed momonts.lI N T R O D U C T I O NA large number of methyl substituted benzenes have been investigated both in vapour and solution phases and their dipole moments determined. Using the dipole moment data, the structure of the methyl benzenes has been extensively discussed in regard to their effect on other substitutions and their inductive and resonance effects on the benzene ring itself (Smyth and Lewis, 1940). Similar investigations liavo not so far been carried out with ethyl substitution. Only two of these, namely, ethyl benzene and pentachloro ethyl benzene haye been studied (Baker and Groves, 1939 and Smyth and Lewis, 1940). In the present investigation the dipole moments of six ethyl substituted benzenes have been doteT-mined in dilute solution in benzene, in order to understand the effect of rejilacmg the methyl group with ethyl group in the benzene compounds.E X P E R I M E N T A LThe experimental arrangement and the method of calculation are the same as described previously (Murty, 1967). All the ethyl benzenes were supplied by L. Lights and Co., England and were of analytical reagent standard of purity. The solvent benzene was also of A.B. grade of purity. The group moments and polarisabilities used in the calculation are given below.61Group Moment Polariaability o X 101*4 COCl 1.65 2.51Br 1.60 3.63CaHr, 0.58 4.21492Dipole Moments of some Substituted Benzenes, etc.R E S U L T S  A N D  D I S C U S S I O NTABLE Io-Chloro ethylbenzene493w ®ia AE Af / l P «12 m2 , n Am- AM‘j / i r0 .00962 2.2833 0 .0193 2.007 1 49425 2.23277 0 0 0 2 1 2 0 . 2 2 00 01397 2 .2907 0 0267 1 908 1 49437 2.2d315 0 00250 0 1790 01954 2.2995 0 .0355 1.817 1.49437 2 23316 0 00250 0  1280 03522 2.3241 0.0601 1.707 1.49468 2.23400 0 00341 0.0970 04420 2 .3374 0.0734 1.661 1 49483 2.23451 0 00386 0.0870.05164 2 .3482 0 .0842 1.631 1.49489 2.23470 0.00405 0 078(AH/W) 9Prf - 4 9 .6 c.o. fi ^  1 .57  D.TABLE IIm -Chloro ethylbenzeneW E-j 3 AE Ae/IP Am-0,00730 2  2826 0  0186 2 544 1 49384 2.23155 0.00090 0.1230.02024 2.3159 0.0519 2 .563 1.49408 2.23227 0.00162 0 .0800.03132 2.3d35 0.0795 2.537 1.49423 2.23273 0.00208 0 .0660 04107 2.3661 0 . 1 0 2 1 2.486 1.49459 2,23380 0.00315 0,0770 .05824 2.4063 0.1423 2 .444 1.49479 2 23439 0.00374 0 0040 07949 2  4566 0 1916 2.411 1.49505 2.23519 0 00454 0 0570.09879 2.4988 0 .2348 2.378 1.49545 2.23636 0 00571 0.058(Ae/IT) — 2 658 (AmV H O ^ ^ O - 0  085P , / = 6 6 8 (j.c. /t-^1 .81 D.TABLE IIIp-Chloro ethylbenzeneW Ej2 Ac £ielW W-ii-2 Am- Au-^jW0.03126 2.3581 0.0941 2 .926 1.49429 2.23292 0.00227 0 0710.04401 2 .3840 0 . 1 2 0 0 0 .728 1.49434 2.23306 0 00241 0.0550 .06876 2 .4187 9 .1547 2 .632 1.49444 2 23332 0.00267 0.0450.07469 2 .4516 0.1876 2 .516 1.49468 2.23398 0 00333 0 .0440.09464 2.4943 0 .2303 2.437 1,49608 2.23528 0 00463 0 043'TF—>0 “ F ^ = 8 0 .4  0 .0 ,(A n8/Pf)^_^0=0 080M = 3.00  D4 9 4TABLE IV o-Bromo ethylbenzeneG, M. K .  M u r tyW ^e jW ^n ^ lW0 02250 2 .3184 0 .0544 2 .410 1.40410 2.23261 0.00196 0.0870.03068 2.3604 0 .0964 2 429 1.40461 2.23368 0  00303 0 .0760.0.5608 2.3977 0.1337 2 .384 1.40523 2.23671 0.00606 0 .0900.07352 2.4360 0 .1720 2.339 1.40553 2.23667 0.00602 0.0820 09053 2.4725 0.2085 2.303 1.49605 2.23R15 0.00760 0.0830.10760 2.5075 0.2435 2.261 1 49682 2 24047 0.00982 o.O olr^ i- .8 5 6 c.c. f i ^ 2 .06 D .TABLE Vm-Bromo ethylbenzeneW £,BjW /^W^IW0.01260 2.2045 0.0305 2.423 1.40383 2.23158 0 0093 o\.0740 02231 2.3179 0 0539 2 415 1 49417 2.23250 0  00186 0.0830  02925 2 .3333 0.0693 2 .370 1.49450 2  23353 0.00288 0.0980.04887 2.3793 0.1153 2 360 1.49499 2.23600 0.00436 0.0890.06322 2 .4104 0.1464 2 .316 1.49555 2  23666 0.00601 0.0950  08221 2 .4512 0 1872 2 277 1 49591 2.23776 0#00711 0.'0870 10140 2 4908 0 .2268 2,236 1 49663 2.23990 0 00925 0.091(Ae/W')pp_^0 =-Vd = 8 3 .1  0 .0 .2 .454 (AW'*W)j^_^y —/i =  2 .03  D.0.081TABLE VI ^>-Bromo ethylbenzeneW Ac AelW W-l 2 Aw-“ An'-i/W0.02113 2 .3190 0.0550 2.602 1.49458 2 23376 0.00311 0.1470.03375 2.3642 0 .0822 2.435 1.49499 2.23611 0.00446 0 .1320.04981 2 .3802 0  1162 2.333 1.49671 2.23715 0.00660 0 1310.06814 2 .4194 0 .1554 2.281 1 49637 2.23012 0.00847 0 1240.09230 2.4706 0.2066 2 .238 1.49707 2.24122 0.01057 0 .1140 .12450 2 .5421 0.2781 2 .236 1.49783 2.24350 0.01285 0 .103(A e/T T )^-> 0 = 2 .6 4 0  P(j«=87.2 O.O. ju<=2.0S D .0 .151Dipole Mormnls of some Substituted Benezenes, etc, 495TABLE VIIMoleculeCalculated Vector S & H O bservedo-Chloro e thy l benzene m-Chloro e thy l ben/eno p-Chloro ethy l benzene o-Bromo ethyl benzene m-Brom o e thy l benzene p-B rom o e thy l benzene1.36 1.79 1.C71.91 2  0 1 1.812.13 2 23 2  001.31 2 . 0 1 2 ,061 . 8 6 , 1.99 2 .032.08 2.18 2 .08Table V II shows th at there is considerable amount of disagreement between the calculated and observed values Even when inductive effects are considered the disagreement exists; in fact^ the values calculated by simple vectorial method are better, in particular as we go to raeta and para-chloro ethyl bonsceiies. I t  indicates th a t the induced effects are alight. The disagreement between the calculated and the observed values may bo attributed to the assumed group moment of 0.58 for CjjHg which may be rather high. Unfortunately, there is no solution value available for ethyl benzene. A comparison with the corres­ponding chlorotoluene values reveals th a t the calculated values are 0.22 to 0.28 higher for the Ghloroethyl"benKenes. The slight induced effects present in chloro- ethyl benzenes may be duo to the higher polarisability of the ethyl group.In  the absonoe of induced and resonance effects, the chloro and bronio ethyl benzenes should have almost the same dipole moment as the corresponding substituted toluenes. I t  is also reasonable to expect slightly higher values for ethyl compounds owing to the slightly larger dipole moment and polarisability of the ethyl group. Examination of Table V III (which gives the comparative data) indicates th a t the experimentally observed values for ethyl benzenes support the expectations.TABLE V IIIO rthoCal. Obs.M etaCal. Obs,PttraCal. Obs.Cliloroioluono* 1.41 1.43 1.79 1.77 1.95 1.94Chloro ethy l benzene 1.79 1.57 2 . 0 1 1.81 2 .23 2 .0 0B rom otoluene 1.38 1.44 1.76 1.75 1.92 i .9 3Brom o ethyl benzene 2 . 0 1 2 .06 1.99 2 .03 2 .18 2.08' Moore and Hobbs*(1948)496 C. S , K .The agreement between the observed and calculated vtiJues of chloro and bromo toluenes, the fact that chloromesitylene has the same moment 1.55 as chlorobenzene while bromomesitylene and bromodurene have moments 1.52 and 1.55 respectively as compared to 1.50 for bromobenzene and th a t chloro ethyl benzenes have approadmately same values as the corresponding 1>oluenes show th a t effects of the methyl and ethyl groups upon the structures contributing to the moments of chloro and bromo benzenes as well as the inductive effect between the halogen and the adjacent methyl or ethyl groups are too small to be detected in the moments (ISmyth and Lewis, 1940).In  the case of bromoethyl benzenes there is little variation in observed moment values from ortho- to para- position which is unexpected since for the correspond­ing bromotoluenes there is a definite increase of moment from ortho- to para- substitution. I t  is also interesting to note th a t while the caloulated| values by vector method show the increase from ortho-to para-substitution, m e Small­wood and Horzield method does not give values with any definite indication of increase from ortho- to para- positions. The experimental observations were taken on two different samples obtained a t differnt times bu t the same\ values of dipole moments for the three bromo ethyl benzenes were obtained. I t  is Veit that further determinations on dipole moments should bo earned out on other poly- substituted benzenes containing the ethyl group before attempting an explana­tion of the observed moments.A C K N O W L E D G M E N T IThe author is deeply indebted to Prof. K. R. Rao ior bis kind and constant guidance.R E F E R E N C E SBalter, J .  W ,, and  Groves, L. G., 1939,, Jour. Ohem. S oq., 1144.Mooro, E . M., and H obbs, M. E ., 1949, Jour. Am. Chem. Soc., 71, 411. M urty , C. R . K ., 1957, Ind. J . Phys., 81, 266.S m yth , C. P ., and Lewis, G. L., 1940, Jour. Am. Gfiem. Soc., 62, 721.

Dipole Moments of Some Substituted Benzenes and Pyridines. Part III. Chloro-and Bromo Ethyl Benzenes

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Dipole Moments of Some Substituted Benzenes and Pyridines. Part III. Chloro-and Bromo Ethyl Benzenes

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