Mehrotra, N K

Pant, D C

Saxena, M C

Somevanshi, S K S

English

IACS Institutional Repository

Microwave absorption and molecular structure of polar molecules in solutions, relaxation times and activation energies of some substituted benzenesD. 0. Pant, 8. K. 8. SoMiovAKsni. N K. Mehrutra, M. C, Saxena Phi/sics Peparl'moU, Liu liiow Liic/cnoir( / i ^ e c r i v r d  -4 197(), i r r i s v d  2  I^ 197(4)Indian J .  Phys, 51A, :^,0S-312 (1977)Tiio pro,son! oommuaioalioii j'0])orls l-lio rola-xation imioB of 3-5 di- cliloioiiitro 1)(‘U7ou(\ 2-5 difliloi'nnil ro))(‘t\7ono, 2-5 (lil)ro)m>niiro bonzfau  ^ y>-))i‘uJiioniijol)oir/oiM\ 2-4 dinitjoclLloioboiizcau'. 1.2,4 di- iiitn)(‘1il(H’() lKai/,(‘tu‘ ill (hiu1(‘ .solulioiiH of bou/.iaio at AvaYoIoiip^ ili 3*13 0111 (9585 Mo/iSoo) in tlio iiiion^wjivo m*ion. Tlio moasuroiii(*utH liiivo |)o(‘n lujult' a-t 20 , 30' and 40'ff in onlor to oaloiilato tin' frcM' onca|rios of iutiv^atioii i’ni of dip»»lo oriontatioii ami visoousflow. It is conoliuliHl tliat tho dipolo oriontatioii is mainly contri- bntod by niolocnlaT rotations Prom tbo valuos of AFr for ilio \Miions roni])onn(ls iiiA( s^tigatod infcnouco lias broji dimvii lliat onorgy of activation incroa.sc^ s v illi tli(^  size of molecules.I . I'lXEO RYRolaxatiou time b a s  boon determined using tlie Goncmitrot ion variation method of Gopala Krishna (1957) given by t,lie relation as discussed iu an oarliei paper (1909)( 1 )27TC L dxDielectric relaxation moclianism may be explained in terms of absolute rate thnory (1941) by treating dipole orientation as a rate process in which the polar molecules rotate from one equilibrium position to another. This process of rotation requinis as activation energy sufficiemt to overcome the energy barrier soparatiiig the two mean equibbrium positions and is given by-  ( ^  )oxp ( -A S tI£) exp (AHrjltT) (2 )AHj is calculated from the slope of log Tr vs 1/T plot as shown in Fig. 1 and 2. The intercept of the plot log Tr vs \jT gives tlio factor Ae'~^ '^^ IE). AFrand ASt are calculated using the equation given in the earlier paper (1972).The concept of viscous flow of a liquid as a rate process that involves the surmounting of a pot-oiitial barrier has led to an analogous equation for viscosity of the solvent, benzene ;= Boxp(—AS7ilB)exp(AH7ilBT) ... (3)30530fi P an t, Som evanshi, M ehrotra, Saxenais obl-aiuod from the slope of plot, log ?/ against }jT as shown in graph 1 . B has bo(3n calculated from the intercept of tiro plot log // vs l/7\ and A/S)/are obtained from the equation given in the paper (1972)Whiffen & Thompson (1946), Gopala Krishna (1958) and Shobhandri (1960) have found energy of activation, for viscous flow of solvent to be alvays greater than AFr- Saxton (1952) and Van Eiek <Sr Poley (1957) have observed tliat AFr and Ai^ \, are nearly equal in case of some pure liquids. Bhaiiumati (1963) hav(3 indicated that AFr and AjP„ are nearly equal only in case of lowviBOosity Bolvonts. Smyth and follaboralors (J94y, 19G0. 19(iJ) httvc. found A to inoroaso with sizf^  of moJocule.Absorption and structure of polar molecvlss in solutions 307Fig. 2A study of abovo rosults indicaio that dofinito eomhiBion can not be drawn regarobng the variation of onergios of activation wnth the sizo, shape and nature ot the molecules. The pivseut investigation, Iheveforo, has boon undertaken to stud}’' the dielectric relaxation in relation to jrioloeular structure and to fuithei our knowledge about- the variation of energies of act-ivation for dielcetrio relaxa­tion and viscous2. E x p e b im k n t a i .Chemicals : All the compoundH used are of purest quality obtained from Messrs Briti>sh Drug House Ltd., England. Purest, quality Analar Benzene obtained from Messrs B. D. H. was distilled belore use.308 P an t, Som evanshi, M ehrotra, SaxenaA rnicroAvave boricli of 3*13 cm, TOVcJengtli region has been used for measur- ing the di(doetric eonstant, v! and tlio loss lad or, f/', of the dilute solutions of eora])ounds in iKuizono. The standing wave tecliniciue of Ptoberts cSr Von Hippel (1940) and its subsciquout simplification by Dakin k Works (1947) is used for calculating values of dieloctri(; constant and loss factor. The measurements of d are accurate i.o iliose for d' relaxation times obtainedby er>nO(aitration variarion method of Gopala Krislnia (1957) are found to be accurate to H“0*5%. Tln^  vjilues o f// of solvent- benztme are 0-47 X 10~^ , 5-01 X 10~“ and 5*23XlO~® poist^  at 3()'’C and 40°(/ respectively.3. K esults'The values of dioled-ric constants (e') and losses (r,") for solutions of increas­ing eoncoutratious at various t(mipera.tui('S ar(‘ given in table J , Tii tal)lc 2 theTable 1 . Exporimonral data for the detiumiinat ion ol ifdaxation timesOompouiidConccn-iral ion co -■2frC 30"(J 40"C[1) 2'5dit*hlorf)-(2) 3-5 dicbloro- tiitrobonzoiit'(3) 2-5 dihromo- iiitrobonzono(4) p-bromi). nitrobenzom'(5) 2-4dinitro- nhloroboiizoiin(6) 1-2 dinilro 4- chlorobouzoup0220 2.31221 0.01771 2.32011 0.03071 2.34101 0.0310J,02‘IS 2 32253 o.o5(;2(i 2.37215 0.00532 2.34513 0.035050281 2.344()2 0.07858 2.3S3(n 0.07408 2.30184 0.001010305 2.3S301 O.0C012 2.4I5S3 0.0SS75 2.30002 0 . (H \ n i20320 2.30418 O.0!)087 2.41020 0 08021 2.41110 0.08090. 0200 2.20501 0.00434 2.31221 0.10031 2.34240 0.02091.02S1 2.20800 0.00800 2.35075 0.12110 2.31321 0.03274. 0200 2.30521 0.0747.8 2.30084 O.M008 2.35015 0.050880321 2.30832 0.07803 2.4211(1 0.17512 2.38703 0.00320.0.341 2.31513 0.07032 2.48013 0 23844 2.40821 0.08105.0231 2.28721 0.00087 2.20501 0.07704 2.32103 0.08028.0253 2.31033 0.11508 2 32043 0.10080 2.33084 0.11532.0200 2.30054 0.17322 2.35410 1.13078 2.30405 0.1308102 SI 2.37310 0.10804 2.38322 0.18322 2 38743 0,17030.020S 2.37027 0 20125 2.30903 0.10051 2.40321 0.18592.0102 2.21001 0,02031 2.21832 0.02005 2.23041 0.03420.0202 2.2312S 0.0301H 2 20212 0.03100 2.25312 0.04512.0342 2.23510 0.03108 2.20098 0 03511 2.25810 0.05823.0375 2 .2  1228 0.04310 2.27302 0.04412 2.20014 0.00321,041(J 2 !25398 0.04510 2.28700 0 O1500 2.27893 0.07913.0301 2.20023 0.04002 2.28021 0.05402 2.2S502 0.05832.0352 2.27SM 0.05815 2.20841 0.00075 2.30481 0.07170.0301 2.32412 O.llOHl 2.31052 0.12143 2 35023 0.11243.0402 2.39050 0.18871 2 .350S4 0.12305 2.30124 0.11827.0501 2.11032 0.19023 2.30120 0.12480 2.440S5 0.10421. 007S 2.20021 0.04058 2.28021 0.05402 2-28390 0.06836.0132 2.27713 0 .05SOI 2.208)5 0.00059 2.30439 0.07129.OISS 2.33280 0 . )1072 2.31020 0,11139 2.35332 0.11249.0241 2.30049 0.18081 2.35080 0.11008 2.35738 0.11892.0200 2.40128 0.10002 2.36124 0.12010 2.44080 0.19318values'of relaxation times (t) anti thermo-dynamic paiamclci H for dipoh> orienia- tion and viscous flow have been reported. The values of A' and B' alougwilh Eyring’s estimated values of A and B are given ijx table 3.Table 2. Relaxation times and iiular energy parametersAbsorption and structure of polar molecules in soluiions 309^ F t ^F' )^ ANr AS j] A//t AllyCompoimd Ten\p. T X 101“ Koal/ Kcal/ Cal/me 1 ('*al /in ol K c£i1 / K('ul/"K Sec.. 111 el niol mol mol(1) 2,5 cUchloro- 293 11.87 2.4S 2.00 — 0.81 - 1 .2 !) 2.25 2.52nitrobenzene 303 10.72 2.52 2 92 --O.S9 1 . .32 2.25 2.52113 9.6fi 2.57 2.04 -  1 .02 - 1 . 3 1 2.25 2.52(2) 3,5 dichloro- 293 14.31 2.59 2.00 - 1 .0 3 — 1.29 2.20 2.52nitrobenzene 303 12.97 2.64 2 - 1 , 1 5 - 1 .3 2 2.29 2.52313 11. si; 2.09 2.94 - 1 .2 8 - 1 .3 4 2.29 2.52(3) 2,5 dibroino- 293 21.51 2.82 2.90 - 2  01 - 1.29 2.23 2 52nitrobenzene 303 19.97 2.89 2.02 -2 .1 7 — 1.32 2.23 2 52313 IS.Sli 2.07 2.04 — 2.38 - 1 . 3 1 2.23 2.52(4) y5-bromo- 293 8.21 2 .27 2 .90 - 1 .53 — 1 .29 1 .82 2 .62nitrobenzono 303 7.32 2.31 2 .02 _ 1  .01 1 .32 1.82 2 52313 0.28 2.35 2.94 — 1 .09 — 1 . .31 1.82 2.52(5) 2,4 dinitro- 293 15.42 2.03 2 00 — 2.18 — 1.20 J ,98 2.52cliloj'obonzoiie 303 14.58 2.70 2.92 - 2 .3 7 - 1 .32 1 .08 2 52313 13.07 2.77 2,91 - 2 .50 — 1 :m 1.08 2.52((i) 1,2 dinitjO'4- 293 17.53 2.71 2 .90 -  1 .77 — 1.20 2 JO 2.52clilorobeii/eaie 303 10.40 2.78 2.92 - 1 .94 — 1 32 2.10 2.52313 15.39 2 .85 2.94 - 2 . 1 4 ^1.34 2.10 2.52Table 3. Relaxation Times and Factors A\ B', A iiud BA  V MM - K - lijK Ii{r--hNIVCompound Temp, T X 10^ ^ XlO” B'i -J xlOii y KJf*iSee.(1) 2,5 dichloro- 293 11.87 6.54 8.57 4.80 4,40nitrol3(mzoiio 303 10.72 4.84 8.58 8,80 4.44313 9.06 1.50 8 00 4.80 4.38(2) 3,5 dicliloro- 293 14.34 0.99 8.57 4.80 4.49nitrobonzeno 303 12.97 0.43 8.58 4.80 4.44313 11.80 5.90 8.60 4.80 4.38(3) 2,5 dibroino- 293 ^ 21.61 11.91 8.57 4.80 4.49nitrobenzene 303 19.97 11.22 8.58 4.80 4.44313 18.80 10 64 8.00 4 80 4.38(4) p-bromo- 293 8.2] 11.35 8,57 .30 4.49nitrobenzeno 303 7.32 11.19 8.58 .80 4.44313 0.28 12.01 8,00 .80 4.38(5) 2,4 dinitro- 293 16.42 7.07 8.57 .80 4.49chlorobonzono 303 14.68 7.40 8.58 .80 4.44313 13.07 7.18 8.00 .80 4.38(6) 1,2 diiiitro-4- 293 17.63 8.35 4.57 .80 4.40chloro bon zone 303 16.40 8.85 8.58 .80 4.44313 15.39 8.29 8.00 4.80 4,38:^ io Pnnt, Somovanshi, M ehrotra, Saxena4. lOisciissiONrelfixatioTi Ijitie oi‘ 1^ ,5 didjluronitrol)oj»ZMU  ^ is ]aj'^oj‘ limn llmt <A' 2,5 dicliloronitro l>oiiz('n(;, llir r-izc of lb(i boll^  iiiolocnlos is same. This can1)0 i*.\f)lMino(l by cousidoring 1h(‘ fact- tbnl in 2,5 dioldoronitrohoxizojio hoth chJoriiio at.nms ar('at' j)ura ])f)sHions i.o (nioIi nt]i(*r iioiico llic di])olo foinn'd is Avoak, M'liik- in .‘1,5 dip'llloronitro laaizono botJ) (Oiloi'im^  alonis art' a1 niola prsition to llio nilro LO'oup wliioli diM^ to uo^ativ(‘ nu’ o^inorif* vdTocI ])rodiuo,s gi(‘ator sloiio, hindrance to (hi rolaiion ortho inolociilo ri'snllin^ iji vrln(' of relaxationt-ijiic.. 2-5 (iil)»*omonitTo InmzoiK' (‘xhibils higliiT rclaxatir.n tinii^  than other oorjipounds oCthi^  scj-ii‘s whicln is due to tlic lajg(a size of tin iiiolecuJc^  and stjong polarity ofthi^ bT'oino gi'mip. p-bronionitro benziaii^  possesses the lowest reJnxa- t.ioii time \\’hieli eaji Ix^  i‘X[)lained not only dne to th(^  smallest size oi the molceide but. also due to the iaet. that both the substituted gJouj)S i,e nilio and Ijioino groups are at pt ra position with eri^ spf'Ct of each otlu'r.II. is ol)Sf rved *rom the tables that the clieledrie ridaxfdion time of 2,4 di- nil,i ((‘hloroboiizeijc is larger than that of 2,5 diidiloronitlobenzciH  ^ A\hieli is duei.o lh(^  larger sizi of iormer molecule and the stioug polarity of the iiitio gioujis 1.2 dinitri' 4-ehloiol.enz(ai(  ^ (exhibits highi*r relaxation time than that of 2.4 dinitro chlorobmizene. This can not be (‘xplaiiied rm the basis oi‘ ])eb^ >.-'s (1929) (4onee[)tion. as tJii' size ot both the nioliaailes is same, This can be attiibuted to tb(^  laager rolumi  ^ sA\e[it- oul. for' dipole ojiiaitataoii liy tli(‘ roiniei inolecnle.T h a i i u u i f f u i t i n i c  p n m m c i r r u s'I'he liiM* imergii^ s of aetiva-tion Jor hoth the process ot diidectiie relaxation ami viscous How increases with incii a^sing teinpoiature Avhile tlii^  relaxation tami^  d(‘cr(xis(‘s. Tliis is due to the (act that, at' highci’ tenijunatuic the inoliaailai collision ra.ti‘ increases with the ix^ sult that energy lecpiired to bring molecules into activated state will also iiieieaiSi'. Similar residts Iuia^ * also been obtained by Mehrotra aaid ( lollabora.tors in case oJ some substituted anilin(^ s and anisoles(1972). 2-5 dibronioiiit robeiizene molecule has the highest Amine for the freeeiie,r!iy o( actlA^ 'a-taon for dioleetrie relaxation and the p-bronionitrohenzene exhibits tlii^  loAvest. value. This can lie attiilmti'd to t.Ki^  faet, that the former molecule eN])m’ieiie(^ s the maximum lesistanee in dijinlar lotation. Avliereas the lattm- exp(‘rieiu^ ^^ s tlie haist, hindrance. It has been ob.soiwed from tabic 2 that, activat ion enei’gy for dipole orifuitation ineri^ asc s A\itb size and .sliapit* ormoleeuh's wliieh in aeeordaneo with the results fiblaincal by Smyth and collaborator (1948, 1950. 1901)It has be(‘ii found tlmt the Ireo eiuugy of activation fc»r viscoAis flow process is alAvays greatia* than that, for tlu^  diel(‘et,ri(* relaxati(»n process in all cases inA-estigateiL This is due io tlu‘ faet that tlie process of A'iscous Hoav iimilves !)oth rotatjoii and translation, wliile the process of dipole orientation iinmlvts(Hiiy tho rotation of llir mojoc‘ijl(‘. SimilaT' r(\sults liavo onrlioi' hern obporvocl Pc'tro & Smytli (1957). Krislmaji (19(i5) and t \\(> (d'llu* aiitliors (J9(i9 ) ImiHIum’ the ratio ol AF  ^ and AF,, a|)]'iroaches unity for MUiie (vf llu' e(Uuj>ouiul^  imenli- gated, wJiieU suggents tlial the moving um(s particu i^ating in Iavo pvoetss aje idontieal and that aetivation lakes jiliui' in snmi^  of freialom liec^ anse thesam(^  bonds have, lo be bi oken befori' (‘itlnu’ mol ion is possible'.The most probable cmlhaljiies of aetivaiion are loss lhan the eoires]HHidmg free enei'gies so tliat mosi pr'obabJy oidi’ojiies of aetiA'alion are' negatiA(‘, Aeeord- mg to Branin Smyth (1951!) a- negatiAai (aitiopy of aelivation mdif'at(\s (bat 1h(^ L-o aie foAVtu' eoutigmatKuis possible in (he ae l^ivated state's and ibi' 1la'S<' (‘on- figurati(ms ac'livated si,ale is mnn^  ouh'ii'd tluiii tln^  norma! sla1(' bi'eaii.si^  ni aetivated st.ate di]K>ks try to align in tin' din'ction ol a]ii)lied held whicli sJioidd obviously b(^  more ordej-t'd. Tliis mdieiih's the ('xisteiiee ol eoopiaatiAa' ojieida- Lions of the moh'ent's iisnltiuv troin steric foiei'S, Similar k '.kiiMs have' b('('ii obtained by Man Singh (IbbJ), Kong Smyth (J9t».H) and by one of (In^  authors (1909).Tlu' vui/lnes of .K ( -  given in table II are found to vary lilt.It' Avit-httmipej*atiir(^  for one s(»lntioii but ait? different lor solutitnis having difleK'Ul. polar molecules varying from 4-50 to 12-01X 10“ This indicates that th(‘ observed values oC this factor differ v idely from t lu'oietical A^ aluoX vvJiere. .4 is ecjiia] to ////* as shoA\m fiy ,Kyring and theexponoiitial faettir has btjon taken to be neatly (HTjual to 1 as AaSV JB a very small quantity.As given m l.ablo I;, factor B' Be Avhicb is very mnirly equal toB, varies littb' Avitliin the observ(.'d range ol teuqtorature and is ttearly twict^  the Eyring's (estimated Andu(^ s ot hNjV for the* froqueuey factor B. It may tlu'i'cfore be (-fiiieluded that, freqiieuev factors A and B are not constants and aro better re]>resenterl by A' and B\ tin* now factms one of Avhieli A' is appre­ciably influenced by tlu. nature of the tuoleculo and tern per a.tur<^  and is always greater than the Eyring's value A (^  hik). The factor B' differs from lactor B but does not vaiy ajipreciably Avitli temperature or the nature of the m(4eeu]c‘S. Similar results were obtained by Shulda and Avorkors in case ol b(mzald(diyd(^ s (1968).Absorption and structure of polar molecules in solutions 3 1 1A o k k o w l e d g e m e n tThe authors are deeply indebted to Prof. B. G. GokhaJe, Bead c4 1h(^  Depart­ment of PJiysics, Lucknow University, foi his continued int,crest and encourage?-^  ^meiit tlmoughout the progress of lh(i w(Ark. ':U2 Pant, Somevanehi, Mehrotra, SaxenaBefisbsnoissl^ liiimuital j A. Indian J. Pwc Appl. Phys. 1, 148.Brauiu F. H. <fc Sm;vth C. V. 1952 J. Cham. Phys. 20, 112 1.Dftkiii T. W. k Works C. N. 1947 J. Appl. Phys. 18, 010.Do boy P. 1920 Polar molecules, Chomical Cataloguo Company, p. 90.ICyriug 11., ClaHKirmo S. k Laider K. J. 1941 The Theory of Pale Processes. McGraw Hill Book Co. luo., Now York, p. 458.Fong F, K. k Rinyih C. P. 1902 J. Amer. Chem. Soc. 85, 548.Cmb E. L. k ,Smyih 0. P. 1901 J. Amer. Chem. Soc. 83, 4122.Hoston E, J., J-loHion W. M., Rinylli C. P. & 5r. 1948 J. Amer. Chem. Soc. 70, 4102.Kiilmiuin O. F. & Rmyth C. P. LOGO ,/. Auter. Chew. Soc. 82, 782,Krisliuii V. K. Copala 1957 Tra)is. Faradaif Soc. 53, 707.Man Singh A. 1901 )od. J. Pure K/ Phys. 2, 23.Mohrolni, N. K.. l^ int T, C. iSt Saxona M. C. 1972 Bull, of Chew. Soc of Japan. 45, 350. Mohroii'n N. K’.. Pant T, C. & Saxona M. C. lOtiO Trans. Farday Soc. 65, 2079.Poi.ro A. 3. & Smyth C. V. J9G3 J. Amer. Chew. Soc. 85, 548.So])hainlri 3. lOiiO Trans. Far. Soc. 56, 509,Sliukla J . P., Shukla D. D., Ahmod S. 1. k Saxona M. C. 1908 Journ. of Phys. Chew. 72, 1011, Van Eiok A. 3. k Poloy 3. P. H. 1957 Appl. Sci. Pcs. 6B, 359.Wliiiron D. H. k Thfnnpsun 11, W. 1940 Trans. Farad. Soc. 42A, 114.

Microwave Absorption and Molecular Structure of Polar Molecules in Solutions, Relaxation Times and Activation Energies of some Substituted Benzenes

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Microwave Absorption and Molecular Structure of Polar Molecules in Solutions, Relaxation Times and Activation Energies of some Substituted Benzenes

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