Rao, D V G L Narasimha

English

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DIPOLE MOMENTS OF SOME ALIPHATIC AMINESD. V. G. L. NARASIMHA KAOPhysios Detahtmunt, Ahdhha University, Waltair {Received, December 1958)ABSTRACT, The dipole moments of oiglit higher members of the aliphatic amines have been determined in solution in benzene at 30°C and the results are disoussed.in the light of their inoleoular structure. Apart from the fact that the reported values of the dipole moments ore new, the investigation was undertaken as a rornplomentary to measurements on the same molecules in the oentimetric region.I N T R O D U C T I O NThe apparent polarisations of ammonia and its mono-, di-, tri- methyl and ethyl derivatives have been studied in the solvent benzene by Le Fevre and Russell (1947) and Barclay, Le Povre and Smythe (1950). The latter authors have also extended the investigations (1951) to a-propyl and w-butyl amines for which the variation of moment with stlite is studied and also the apparent moments in solution of certain other amines. A positive solvent effect is noted by all these investigators. From a study of the moments of eighteen aliphatic and aromatic amines in seven non-polar solvents and of fifteen liquid amines in the pure state, Cowley (1952) could show that in most cases the solvent effect is small. The solvents benzene, toluene and dioxane gave small positive solvent effects confirmhig the previous results but with other solvents a small negative solvent effect is the more usual observation, Variation of polarisation with change of concentration from iufimte dilution to the pure solute is also studied and is shown to depend on the type of amine and also on the value of its dielectric constant. The dipole moment values are corrected for the atom polarisation which is assumed as 5  per cent of the electron polarisation.The aliphatic aminos may bo considered as substitution products of ammonia in which one hydrogen atom is replaced by an alkyl group. The bond angle of ammonia (109°) may be taken as evidence of the existence of hybridized orbitals. I t has been found that the lone-pair contribution to the resultant moment is much higher than in the case of water. Arguments similar to those of ammonia also apply to the aliphatic aminos. The low moment of tri-meihylamme may be explained as due in part to the wider bond angie compared to that in ammonia, with the result that the lone-pair orbital has less if-chataoter and hence makes a smaller contribution to the dipole moment.6162 D, F. Q, L, Narasimha RaoTill now all obsciwatioiiB are confined only up to butylamine. There are jio investigations on the still higher aliphatic amines, A systematic study of eight higher members of the homologous scries, starting from amylamine to decylamine, is made by the author, the ineasuroments being carried out in solution in benzene at 3()"C. Not only do the results serve as an extension of the previous work, they also provide a useful check on the values derived by the author from measurements made on the same molecules in the microwave region (to be published shortly).E XP J J R I ME NT A LThe experimental technique and the method of coinjiuting the moment from the observed data are described iji an earlier publication of tlio author (1956),HEHUL^J’S AND DI S CUS S I ONThe detailed observations of dielectric constant and refractive iiidex arp presented in Tables 1- to VTII and the consolidated results arc shown in Table IX. For completeness, literature values on the lower imunbcrs of the series (8 mith, 1955a) are also given in Table JX.Let us assume a bond angle of 110° in rnethylajuine, a set of reference axes with the N atom at the orighi and fix the x-ai|is in the axis of syimnetry (of the parent NH^) and choose the a;y-plane to pass through the C atom. The moment eompojients outside the plane of symmetry cancel one another. The boi^d moments may be derived from the values for ammonia (1.45D) and trimethy- lamine (0.641)) as3(H -N ) cos 6 8 ° =  1,45 H -  N =  1.293(R -N ) cos 70° -= 0.64 R-N 0.62 0 -  N -- 0.22Using those values, wo get for methylamine=  (R-N) cos 70° +  2 (H -  N) cos 70° =  1.09 My =--■ (R-N) sin 70°+2(H-N) sin 70° sin 30° ==-0.63 /<, =  1.26.The calculated value thus agrees well with the gas value of 1.28. I t  may be shovm that the angle between the molecular dipole axis and "the C-N bond direction is 30°+70“ — 1 0 0 ° (Smyth, 1955). The calculated value for all the other higher animes (only one H atom of NH3 is substituted) is the same as for meihylamine, except for some induced effects of the primary dipole on the hydrocarbon chains. !t is known that the dipolo axis in methylamines is not far from perpendicular to the direction of maximum polarisability and hence the solvent effect causes the apparent moments in solution to he higher than theTABLE I w-AmylamiueDipole Moments of some Aliphatic Amines 5.3An2 ^n^jw(- )  ( - )0.01636 2.3065 0.0426 2.600 1.49298 2.22900 0.00668 0.3410.04442 2 3796 0.1156 2.603 1.48976 2.21939 0.01519 0.3420.06269 2.4283 0.1643 2.620 1.48798 2.21409 0.02049 0.3270.08900 2.4951 0.2311 2 596 1 48553 2.20681 0.02777 0.3120.10210 2.5283 0 2643 2.689 1.48306 2.19946 0 03613 0.3440.11960 2 6738 0.3098 2.593 1.48120 2.19395 0.04003 0.3400.13090 2.5987 0.3347 2.557 1 47980 2.18981 0.04477 0.342A =  (Ae/w)w ->o -- 2.60ii Po =  48.61 o.c. B =  (A»i“/w7)w—> 0 =  —0.339 fi =  1.65 i).TABLE II  n-Hexyl amiiieAe 14,22 Ana(- )^n^lw(- )0.01931 2.3083 0 0443 2 292 1.49436 2.22798 0.00660 0,3420 03386 2.3389 0.0749 2.211 1.49102 2.22313 0.01145 0.3380 04774 2.3667 0.1027 2,150 1.48964 2.21902 0.01556 0 3260.07396 2 4180 0.1540 2.082 1.48686 2.21076 0.02382 0.3220.08960 2.4458 0.1818 2.031 1.48600 2 20522 0.02936 0.3280 10280 2.4664 0.2014 1.959 1.48339 2 20045 0.03413 0 332^  =  2 320 B = -  0.331 A - 50.81 o.c. =  1 69Z>TABLE H I w-Heptylamincw AE A«/ry n^<i An2( “ )An^ /ty( - }0.01372 2.2916 0.0276 2.011 1.49326 2 22081 0.00477 0.3480.02904 2.3231 0.0591 2.036 1.40158 2.22482 0.00976 0.3360.04266 2.3483 0.0843 1.982 1.49003 2.22020 0.01436 0.3380.06176 2.3837 0 1197 1.037 1.48810 2.21444 0.02014 0.3260.07604 2.4060 0.1429 1.904 1.48678 2.21050 0-P2408 0.3210.09217, 2.4374 0.1734 1.881 1.48467 2.20425 0.03033 0.3250.10490 2.4510 0.1870 1.782 1.48340 2.20048 0.03410 0.325A =  2.040 J? * -0 .3 3 2 Po = 51.76 o.c. fji =  1.60 P.54 D. V. G. L. Narasimha RaoTABLE IV %-Ociylaminew «ia Ae Ae/w» Wl2 n-i 32 An-2( - )An-2/io(- )0.00673 2 2732 0.0092 1.374 1.49423 2.23272 0.00186 0.2760.01263 2 2809 0.0169 1.351 1.49364 2.23097 0.00361 0 2880 02077 2 2920 0.0280 1 346 1.49292 2.22880 0 00578 0.2780.03200 2.3070 0.0430 1.320 1 49182 2.22562 0.00906 0.2780.05841 2.3386 0 0746 1.277 1.48791 2.21899 0.01559 0.2670.09120 2,3768 0.1128 1.230 1,48702 2.21123 0.02335 0.2560.11300 2.3926 0.1286 1 139 1.48525 2.20697 0.02861 0.253A = 1.380 B = -0 .271 Po = 40.46 0,0. /X = 1.421).TABLE Vw-Deuyl aminem; fl2 Afi ni2- An,z(“ )An.2/ty(- )0.0061.6 2.2706 0 0066 1.078 1 49433 2.23301 0.00167 0.2560.01369 2.2785 0.0146 1.0.57 1.49377 2.23136 0.00323 0.2360.02216 2.2877 0.0237 1.070 1.4931.3 2.22944 0.00514 0.2320.02966 2.2940 0.0300 1.014 1 49267 2 22777 0.00681 0.2300.03749 2.3014 0.0374 0.997 1.49171 2,22520 0.00938 0.2600.04500 2.3082 0.0442 0.983 1.49111 2.22342 0.01116 0.2480.06039 2.3219 0.0579 0.059 1.48971 2.21925 0.01533 0.254A =  1 090 B  = -0 .244 P„ = 39.770.0. /i. =  1.41 DTABLE VI Ifloamylaminew Ae diSfw M|2 Aw3( - )An-2/w( - )0.01242 2.2960 0.0310 2.494 1.49348 2 23048 0 00410 0.3300.02973 2.3394 0 0754 2.536 1,49187 2 22507 0.00961 0.3200.04033 2.3672 0.1032 2.660 1.49041 2.22132 0.01326 0.3290 06860 2,4141 0.1501 2.562J ].48829 2.21601 0.01967 0.3340.06960 2.4404 0.1764 2.535 1.48720 2.21176 0.02283 0.3280.09186 2,4913 0.2273 2.475 1.48466 2.20418 0.03040 0.3310.10650 2.5200 0.2660 2.426 1.48295 2.19913 0.03546 0.336A  2.540 B = -0.330 P*0 == 47.40O.O. fi =  1.63 Z).Dipole Moments of some Aliphatic Amines 66TABLE VII Isohexylaminew ®13 Ae nv2 nia'-i A«-( - )A«2/w( - )0.01114 2.2929 0 0289 2.592 1.49371 2.23117 0.00341 0.3060.02810 2.3235 0.0595 2 575 1,49255 2,22770 0.00688 0.2980.03402 2.3536 0 0896 2.632 1.49152 2 22464 0.00994 0.2920.04381 2.3845 0.1205 2 761 1.49057 2.22179 0 01279 0.2920.05331 2.4137 0.1497 2.809 1.48973 2.21928 0.01530 0.2870 06032 2.4379 0.1739 2.S83 1.48907 2 21733 0 01725 0 286A =  2.390 B = -0 .294 Po =  51 44 c.c. jU =: 1 .GOD.TABLE VIIITertootylaminew ®13 nia Aw'J( - )^n'^fw( - )0.01243 2 2759 0.0119 0.965 1 49373 2.23122 0.00336 0.2700.01972 2.2825 0.0185 0.938 1.49303 2.22913 0.00545 0.2760.04153 2.3050 0.0410 0.988 1 49152 2.22463 0,00995 0 2400.05181 2.3123 0 0483 0.931 1 49018 2 22064 0.01394 0.2690.06963 2.3306 0.0666 0.956 1.48845 2.21547 0 01911 0 2750.07893 2.3390 0.0750 0.9.50 1.48786 2.21373 0.02085 0.2640 09919 2.3589 0.0949 0.957 1.48581 2 20763 0.02695 0.2720 11660 2.3748 0.1108 0 950 1.48458 2.20397 0.03061 0 262A = 0.950 B ^ -0 .206 P(, = 29 . 79 c.o. ^  1 22 D.TABLE IXCompound FormulaAmmonia NHaMothylamine CH3NH2Ethylamine CHaCB^aNHan-Propylamine CH.3(CH2)2NH2n-Butylamine CJIa(CH2)aNH2sec-Butylamine CHaCHNHaCHaCHatert-Bubylamine (CHa)aCNH2n-Amylamine n -Hexylamino n-Heptylamine w-Ootylamin© n>Deoylaine Isoamylamine Isohexylamine Tertootylamine'''value of Le Fovre mid Bussell (1Q47)""•'values of Barclay, Le Pevre and Smythe (1951)CHa(CHa).iNHaCH„(CH2)bNH2CH3(CHa)flNH2CHa(CHa)7NW2CH,(CH3)0NH2(CJI a) aCiEI(CH 2) aNH a(CH3)2CH(CHa)sNH2(CHa)3CNHa(CHa)4Author L iterature valuuM/ l y_ 1.40* 1A5D— 1.46 1 28— . 1.37 0.99_ 1 32 1.17*— 1.32 1 00*— 1.28 —1.29 —1.55 _ —1.59 — —1.60 — —1.42 — —1.4] — — .1.53 — —1.60 — —1.22 — —values in solution in benzenef ly  values in the vapour state.56 D, F . 0, L» Narasimha Raogas values (i.o., a positive solvent effect). I t  is seen that for all the amines listed in Tabic IX for which the vapour values are avail- able >  /ly. Cowley (1952) also observed a positive solvent effect for 7i-propyl and ?i-butyl amines in all the solvents he used. This may perhaps explain the values obtained in this investigation. But, when compared to the literature values on the lower members, the author’s values appear to be slightly high for some of the mole culos. The following points may be noted *(1 ) As we go higher up in the homologous series, there is a tendency for a decrease in the moment. This is in conformity with the conclusions of Smith (1955b). As is already shown the resultant moment of the primary dipole is inclined at an angle of 100'’ with the C-N bond. Consequently there is rather a greater change of the induced moments opposing the primary moment than assisting it.(2) The moments of the normal and iso- compounds are almost the same.(3) The moment of the tertiary amines is a little less than that of the normal compound. A difference of 0.20 is obtained between 7i-octylamine and tert- octylamino. The corresponding difference is 0.11 for the butylaminos (cf. Table IX).(4) A small positive solvent effect in benzene appears reasonable. I t  is probable that a considerable change in the angle from 90° between the mole­cular dipole axis and the axis of maximum polarisability lowers the solvent effect so that the difference between vapour and solution values becomes much less. *A C K N O W L E D G M E N T SThe author is deeply indebted to Prof. K. Rao for his kind and invaluable guidance throughout the progress of work. He is also grateful to the Council of Scientificj and Industrial Research for financial assistance.R E F E R E N C E SBarclay, Le Fevere anrl Smythe, 1950, Trans. Farad. Soc. 46, 912.Barclay, Le Fevre and Smythe, 1951, Trans. Farad., Soc., 47, 357.Cowley, 1952, J. Chem. Soc., 3557.Le Fevre and Rnaaell, 1947, Trans. Farad. Soc., 48, 374.Narasimha Rao, 1956, Ind. J. Phya. 30, 91.Smith, 19.55a, Electric Dipolo Moments, Butterwortbs scientific publicatiens, London, pp. 194.Smith, 1966b, ibid., pp.l95.Smyth, 1965, Dielectric Behaviour and Structure, MoGraw Hill Book Co. Inc. N,Y, pp.311.

Dipole Moments of Some Aliphatic Amines

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Dipole Moments of Some Aliphatic Amines

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