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THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION
BY______ ..Albert .Leroy Myers
e n tit le d
P’ RT'SRH/'INATIOI’ J OF DIPOLE MOMENTS OF SELECTED
COMPLIES WITH THE UNIVERSITY REGULATIONS ON GRADUATION THESES
AND IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS
FOR THE DEGREE OF
-Doctor .of Philosophy.
TO THE LIBRARIAN:-----
1S, THIS THESIS IS NOT TO BE REGARDED AS CONFIDENTIAL.
lie. PKOFESSOH HT CHABGE
GRAD. SCHOOL FORM 9—3 - 4 9 — 1M
DETERMINATION OP DIPOLE MOMENTS OP SELECTED ORGANIC COMPOUNDS
A Thesis Submitted to the Faculty of Purdue University
by Albert Leroy Myers
In Partial Fulfillment of the: Requirements for the Degree of Doctor of Philosophy June, 1950
ProQuest N um ber: 27714115
All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted. In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscript and there are missing pages, these will be noted. Also, if m aterial had to be rem oved, a n o te will ind ica te the deletion.
uest ProQuest 27714115 Published by ProQuest LLC (2019). C opyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346
The author wishes to express his sincere appreciation to Professor Thomas DeVries, who directed this work, for his helpful suggestions throughout the re search and the preparation of this paper. The author also wishes to thank the Purdue Research Foundation, which financed this research through a Research Fellow ship .
TABLE OF CONTENTS
Aliphatic Nitro Compounds................
Organic Silicon Compounds................
Fluorine Derivatives of Benzene..........
Halogen Derivatives of Trifluoromethylbenzene.......
Halogen Derivatives of Benzene with Two Trifluoromethyl Groups............ ..................
Pentafluoroethyl Derivativesof Benzene......
Ether Derivatives of Trifluoromethylbenzene.
Ether Derivatives of Benzene with Two Trifluoromethyl Groups.................. DISCUSSION. ....
SUMMARY............................................... 108 BIBLIOGRAPHY.......................................... VITA......................................... ........
2-Nitrophenylt rimethyls liane......................
Nitroethane in Benzene at 25^................. .
1 -Nitropropane in Benzene at 25°• • ...........
6 . 2-Nitropropane in Benzene at 25°.............
1,1-Dinitroethane in Benzene at 25°• •. »...........
Trimethylbenzylsilane in Benzene at 25°...........
Triethylphenylsilane in Benzene at 25°.......
2-Nitrophenyltrimethylsilane in Benzene at 25°. ••«•
Fluorobenzene in Benzene at 25°...................
4-Fluorotoluene in Benzene at 25°.................
4-Ghlorotrifluoroinethylbenzene in Benzene at 25°. •*
2-Chlorotrifluoromethylbenzene in Benzene at 25°. ••
3,4-Dichlorotrifluoromethylbenzene in Benzene at 25°............................
2-Bromo-5-ohlorotrifluoromethylbenzene in Benzene at 25°..................
2 -0hloro-5 whromotrifluoromethylbenzene in Benzene at 25 0................ *................
8 . TrimethyIpheny1si1ane in Benzene at 2 5 ° • . . . . . .
19 . 5 -Bromo-2 ,4-dichlorotrifluoroniethylbenzene in
Benzene at 25°................................. 20.
3-Bromo-4,5-dichlorotrifluoromethylbenzene in Benzene at 25°........................
21 . 5-0hloro-l,3-his (trifluoroniethyl)benzene in Benzene at 25 0.................................
TABLES (Cont.) Table 22. 23. 24. 25 .
PaSe 4-Chloro-l,3-bis(trifluoromethyl)benzene in Benzene at 25°...
4,5-Diohloro-l»2-bis(trifluorometbyl)benzene in Benzene at 25°..................*...........
4,3-Dictiloro-l,3-bis (trif luoromethyl )benzene in Benzene at 25° 4,5 ,6-Trichloro-l,3-bis(trifluoromethyl)benzene in Benzene at 25°.........
2 ,3 >5 -Trichloro-l,4-bis(trifluoromethyl)benzene
3 -Ghloropentafluoroethylbenzene in Benzene at 25° ••
5 -Ghloro-l,3-bis (pentafluoroethyl )benzene
in Benzene 29 .
benzene in Benzene at 25°.
4-Hethoxytrifluoromethylbenzene in Benzene at 25°••
4-Ethoxytrifluoromethylbenzene in Benzene at 25°•••
4-Isopropoxytrifluoromethylbenzene in Benzene at 25°............
2 -Isopropoxytrifluoromethylbenzene in
Benzene at 34. 35* 36 . 37 *
2-Methoxy-l,4-bis(trifluoromethyl)benzene in Benzene at 25°.......
2-Methoxy-l,3 -bis (trifluoromethyl )benzene in Benzene at 25°.....................
5-Methoxy-l,3-bis(trifluoromethyl)benzene in Benzene at 25°.... .......... ................
5 -Sthoxy-l,3 -bis(trifluoromethyl)benzene in
38 . . 5 -Butoxy-l,3-bis(trifluoromethyl)benzene in
TABLES (Cont.) Tables
39- 4-Methoxy-l,3 -bis(trifluoromethyl)benzene in Benzene at 25°...............*..............
40. 4-Ethoxy-l,3-bis(trifluoromethyl)benzene in Benzene at 25°.....................
41. 4-Propoxy-l,3 -bis (trifluoromethyl )benzene ...... .. ..... in Benzene at 25°
42. 4-1 sopropoxy-1 ,3 -b is(tri fluo romethyl)benzene in Benzene at 25°. ............................
43. 4-Phenoxy-l ,3-bis (trifluoromethyl )benzene in Benzene at 25°*........*.........
44. Experimental Data for the Hedestrand and Guggenheim Equations .....
45. Dipole Moments in Benzene Solution................
FIGURES Figure 1.
Bridge, Resonance and Heterodyne Beat Apparatus
Plate Assembly Container andMixing Chamber.......
Oscillator Block Diagram........ ........... .
Oscillator Circuit Diagram........... ...........
2-Nitrophenyltrimethylsilane in Benzene (D vs. fg).................. .. ................
(Contribution from the Department of Chemistry and Purdue Research Foundation, Purdue University, Lafayette, Indiana.)
DETERMINATION OF DIPOLE MOMENTS OF SELECTED ORGANIC COMPOUNDS 1.
Abstracted from the Doctoral Thesis of Albert L. Myers.
By Albert L. Myers 2.
and Thomas DeVries
Furman University, Greenville, South
AN ABSTRACT The purpose of this work was the determination of the dipole moments of certain organic compounds*
investigated can be classified as aliphatic nitro compounds, silicon-containing compounds and fluorine-containing com pounds*
Dilute solutions of the compounds in benzene as the
nonpolar solvent were used and the Hedestrand^ equation was 3*
Hedestrand, G . , Z* physik* Chem* , /B / 2, 428 (1929)-
employed in the calculation of the dipole moment* The form of the Hedestrand equation used in this re search is:
p2 oo =
M2 - P1 d-L f2
wliereePg **3 = polarization of solute at infinite dilution, s polarization of solvent* Mg
* molecular weight of solute. » molecular weight of solvent. - density of solvent.
£*& = density solution minus density solvent, fg
53 mole fraction of solute.
s dielectric constant of solvent. AD
= dielectric constant of solution minus dielectric constant of solvent.
The dipole moment of the solute was calculated from the equation: yu. = 0.01281 where ^
(P2oe - pe)J
« dipole moment.
Pe 55 electronic polarization of solute. T
- absolute temperature.
Pe , the electronic polarization, was considered equal to the molar refractivity calculated by the Lorentz-Lorenz equation. During the course of the investigation Guggenheim^" pub4.
Guggenheim, E. A., Trans. Farad. Soc. , 4^, 714 (1949 )-
lished an equation for the calculation of dipole moments, and this equation was used also to calculate the dipole moments of the remaining compounds studied. The Guggenheim equation:
) - (n^ -
sdielectric constant of solution,
a* Boltzmann constantt.
* Avogadrofs number.
total grams of solvent and solute
m$ = number of molecular weights of solutes d
= density of solution,
and all other symbols have the same? meaning as in Equations (1 ) and (2 ). EXPERIMENTAL Materials:;--The preparation of pure benzene for this work has been described by Brown^. 5^
After being used in a
Brown, P. E. , Doctoral Thesis, Purdue University, 1949.
determination the benzene was reclaimed by fractional dis tillation.
The 79*9-80.2° fraction was rectified (80 .0°)
and the product was distilled and stored over sodium.
physical constants of this reclaimed benzene agreed very well with the values reported by Rossini^. 6.
Rossini, F. D., Bur. Standards J. Research, 36, 129
(1946). The physical constants and the sources of the compounds studied are given in Table I.
The observed and calculated
molar refractivities as well as the difference between observed and calculated values are given in Table II for all compounds studied. Apparatus and Procedure.— A heterodyne beat method was used to measure the dielectric constant of the dilute benzene solutions.
The constant oscillator was crystal
controlled to a frequency of 100 K.C.
The apparatus and
procedure have been described by Brown^; RESULTS The values for Pg oo and Pe for the Hedestrand equation, and E and 1/0 for the G-uggenheim equation are given in Table III for all compounds studied.
The results of the
determinations of the dipole moments for forty compounds are listed in Table IV, with equation result and sult.
(H) for the Hedestrand
(G-) for the G-uggenheim equation re
Literature values for the dipole moments of these
compounds are included, if such are available.
lated values of the dipole moments by vector addition are also listed, using information and methods given by Weissberger^, Sidgwick^, and Brown^; 7*
The higher ether groups
Weissberger, A . , editor, "Physical Methods of Organic Chemistry", Volume I, Part II, Chapter XXIV, "Dipole
TABUS I PHYSICAL CONSTANTS
Nitroethane 1-Nitropropane 2-Nitropropane 1 ,1-Dinltroethane Trimethylphenyls ilane
1.0390 0.9954 0.9814 1.3528 0.8637
1.3888 1.3992 1.3920 1.4317 1.4881
a a a b c
Trimethylbenzyla ilane Triethylphenylsilane 2-Nitrophenyltrimethylsi1ane Fluorobenzene 4-Fluo rotoluene
0.8612 0.8859 1.0667 1.0183 0.9918
1.4906 1.4990 1.5293 1.4629 1.4664
c c a a
4-Chlorotrifluoromethylbenzene 2-Chlorotrifluoromethylbenzene 3 ,4-Diohlorotrifluoromethylbenzene 2rBr_omo-5-ohlorotrifluoromethyl benzene 2-Chloro-5-bromotrifluoromethyl benzene
1.3325 1.3620 1.4729
1.4442 1.4537 1.4719
d d d
H U1 O S
5-Bromo-2,4-dichlorotrlfluoromethylben zene 3-Bromo-4,5-dichlorotrifluoro methylbenzene 5-Chloro-l, 3-bis(trifluoro> methyl )benzene 4-Chloro-l,3-bis(trifluoro methyl )benzene 4 ,5-Dichloro-l,2-bis(trifluoro methyl )benzene 4,5-Dichloro-l,3-bis(trifluoro methyl )benzene 4,5,6-Trichloro-l,3-bis(trifluoro methyl )benzene 2,3,5-Trichloro-l,4-bis(trifluoro methyl )benzene 3-Chloropentafluoretidaylbenzene 5-Ghloro-l,3-bis(pentafluoro ethyl) benzene
(Continued next page)
TABLE I (Cont.) ”d 5 2,5-Diotiloro-4-tri fluoromethylpentafluoroethylbenzene 4-Methoxyt r1fluo rome thyIbenzene 4-Ethoxytrif luoromethylbenzene 4-1sopropoxytrifluoromethylbenzene 2-Iaopropoxytrifluoromethylbenzene 2-Methoxy-l,4-bia(trifluoro methyl) benzene 2-Methoxy-l,3-bis(trifluoro methyl )benzene 5-Methoxy-l,3-bis(trifluoro methyl) benzene 5-Ethoxy-l,3-bis(trifluoro methyl) benzene 5-Butoxy-l,3-bis(trifluoro methyl )benzene 4-Methoxy-l,3-bis(trifluoromethyl)benzene 4-Ethoxy-l,3-bis(trifluoromethyl)benzene 4-Propoxy-l,3-bis(trifluoromethyl )benzene 4-Isopropoxy-l,3-bis(trifluoro methyl )benzene 4-Phenoxy-l,3-bis(trifluoro methyl )benzene
1.6484 1.2339 1.1837 1.1440 1.1546
1.4251 1.4441 1.4430 1.4437 1.4952
d d d
Prepared in this laboratory by Grilliland, W. L.
Prepared in this laboratory by Benkeser, R* A., and Brumfield, P.
Prepared in this laboratory by McBee, E. T., et al.
TABLE II MOLAR REFRACTIVTTIES AT 25°
«D obs. , 00.
Hit roethane 1-Nitropropane 2-Nitropropane 1 ,1-Dinitroethane Trimethylphenyls ilane
17.08 21. 66 21.62 23.01 50.13
17.06 21.67 21.67
t-0.02 -0.01 -O.O5 4-0.33 -0.02
Trimethylbenzylsilane TriethyIpheny1silane 2-Nitrophenyltrimethylsilane Fluorobenzene 4-Fluorotoluene
55-21 63.75 56.48 25.92 30.78
55-39 64.00 56.35 26.10 30.72
-0.18 -0.25" +0.13 -0.18 4-0.06
4-Chlorot ri fluoromethylbenzene 2-Chlorotrifluoromethylbenzene 3 ,4-Dichlorotrif luoromethyl benzene 2-3romo-5-ohlorotrifluoro methylbenzene 2-Chloro-5-bromotrifluoromethyIbenzene
4-0. 63 4-0.50
5-Bromo-2,4-dichlorotrifluoro methylbenzene 3~Bromo-4,5-diohlorotrifluoro methylbenzene 5-Ghloro-l,3-bis(trifluoro methyl) benzene 4-Chloro-l,3-bis(trifluoromethyl) benzene 4,5-Dichloro-l,2-bis(trifluoro methyl )benzene 4,5-Dichloro-l,3-bis(trifluoro methyl )benzene 4,5,6-Trlchloro-l,3-bis(trifluoro methyl )benzene 2 »3,5-Trichloro-l ,4-bis (trifluoro methyl )benzene 3-Chloropentafluoroethylbenzene 5-0hloro-l,3-bis(pentafluoro ethyl )benzene
(Continued next page)
TABLE II (Cont.)
2-Methoxy-l,4-bis(trifluoro methyl )benzene 2-Methoxy-l,3-bis(trifluoro methyl )benzene 5-Methoxy-l,3-bis(trifluoro methyl )benzene 5-Ethoxy-l,3-bis(trifluoro methyl )benzene 5-Butoxy-l,3-bis(trifluoro methyl )benzene 4-Methoxy-l,3-bis(trifluoro methyl )benzene 4-Ethoxy-l,3-bis(trifluoro methyl )benzene 4-Propoxy-l,3-bis(trifluoro methyl )benzene 4-Isopropoxy-l,3-bis(trifluoro methyl )benzene 4-Phenoxy-l,3-bis(trifluoro methyl )benzene :
rD calcd. CO.
4 RD(o -c )
51.67 37.93 42.59
48.97 36.77 41.39
O CM CM +
2,5-Dichloro-4-tr±fluoromethylpentafluoroethyIbenzene 4-MetboxytrlfluoromethyIbenzene 4-Ethoxytrlf luoromethylbenzene 4-Isopropoxytrifluoromethyl benzene 2-Isopropoxytrlfluoromethyl benzene
% obs* GO .
TABLE III EXPERIMENTAL DATA FOR THE HEDESTRAND AND GUGGENHEIM EQUATIONS ?2oo
Nitro ethane 1-Nit ropropane 2-Nitropropane 1 ,1-Dinltroethane T rimethylphenyl s11 ane
238.19 250.25 268.33 303*84 56.54
17.08 21.66 21.62 23.01 50.13
Trimethylbenzyls ilane Triethylphenylsilane 2-NitrophenyltrimethyIsilane Fluorobenzene 4-Fluorotoluene
68.20 71.88 331.94 71.87 98.21
55.21 63.75 56.48 25-92 30.78
5617 5763 5816
4-0hlorotrif luoromethylbenzene 2-Chlorotrifluoromethylbenzene 3 .4-Diohlorotrif luoromethyl benzene 2-Bromo-5-chlorotrifluoro methylbenzene 2-0hloro-5-bromotrifluoro methylbenzene
5-Bromo-2,4-dichlorotrifluoromethylbenzene 3-Bromo-4,5-dichlorotri fluoromethyIbenzene 5-Chloro-l,3-bis(trifluoro methyl )benzene 4-Chloro-l,3-bis(trifluoro methyl )benzene 4.5-Diohloro-l,2-bis(trifluoro methyl )benzene 4.5-Diohloro-l,3-bis(trifluoro methyl )benzene 4,5,6-Trichloro-l,3-bis(trifluoromethyl )benzene 2,3>5-Triohloro-l,4-bis(trifluoro methyl )benzene 3-GhloropentafluoroethyIbenzene 5-0hloro-l,3-bis (pentafluoro ethyl )benzene
(Continued next page)
TABLE III (Cont.) p2 2 jS-Dichloro-^-trifluorometliylpentafluoroethylbenzene 4-Methoxytri fluo rome ttiylbenzene 4-Ethoxyt rl fluoromethyl benzene 4-Isopropoxytrlfluoromethyl benzene 2-Isopropoxytrlfluoromethyl benzene 2-Methoxy-l,4-bis(trifluoro methyl )benzene 2-Methoxy-l,3-bis(trifluoro methyl )benzene 5-Methoxy-l,3-bis(trifluoro methyl )benzene 5-Ethoxy-l,3-bis(trifluoro methyl )benzene 5-Butoxy-l,3-bis(trifluoro methyl )benzene 4-Methoxy-l,3-bis(trifluoro methyl )benzene 4-Ethoxy-l,3-bis(trifluoro methyl )benzene 4-Propoxy-l,3-bis(trifluoro methyl )benzene 4-Isopropoxy-l,3-bis(trifluoro methyl )benzene 4-Phenoxy-l,3-bis(trifluoro methyl )benzene
TABLE IV DIPOLE MOMENTS IN BENZENE SOLUTION Moments x 10 18 Calcd. >(H) /&(&) Literature Nitroethane 2-Nitropropane 1 Nit ropropane
a c b c
h i 1 i
3.29 3.47 3.35
1,1-Dinitroethane T rimethylphenyl silane
0.44 d h
Trimethylbenzylsilane T ri ethyIpheny1 s1lane 2-Nit rophenylt rimethyls ilane Fluorobenzene 4-Fluorotoluene
0.73 O .56 3.68
0.98 e h
0.80 0.63 3.67 1.50 1.82
5-Bromo-2,4-dichlorotrifluoro methylbenzene 1.09 3-Bromo-4>5-diehlorotrifluoro methylbenzene 0.55 5-0hloro-l,3-bis(trifluoro methyl )benzene 0.99 4-Chloro-l,3-bis(trifluoro methyl )benzene 2.23 4,5-Di ohloro-l,2-bis(tri fluorc>methyl )benzene 1.72 4,5-Diohloro-l,3-bis(trifluorc>methyl)benzene 1.62 4,5,6-Trichloro-l,3-bis(trifluoromethyl )benzene 0.56 2,3,5-Trichloro-l,4-bis(trifluoromethyl)benzene 1.55 3-Ghloropentafluoroethylbenzene 2.31 5-0hloro-l,3-bis(pentafluoro ethyl )benzene 1.10
1.47 f h 2.01 6 i 1.15 f h
1.29 f h
r •o H O
4-Ghlorotrifluoromethylbenzene 2-Ghlorotrifluoromethyl benzene 3 ,4-Diohlorotrifluoromethyl benzene 2-Bromo-5-ohlorotrifluoro methylbenzene 2-0hloro-5-bromotrifluoro methylbenzene
3.19 3.73 3.57 3-70
2.10 1.51 f h
(Continued next page)
TABLE IV (Cont. ) Moment s x 1018 Calcd. /ul(H) /a*(G) Literature 2 ,5-Diohloro-4-trlfluoro methylpentafluoroethyl benzene 4-Methoxytrif luoromethyl benzene 4-Ethoxytrif luoromethyl benzene 4-1sopropoxytri fluoromethylbenzene 2-1sopropoxyt rifluoromethyl benzene 2-Methoxy-l,4-bis(trifluoro methyl )benzene 2-Methoxy-l,3-bis(trifluoro.v methyl^ be nz ene 5-Methoxy-l,3-bis(trifluoro methyl )benzene 5-Ethoxy-l,3-bis(trifluoro methyl )benzene 5-Butoxy-l,3-bis(trifluoro methyl )benzene
4-Methoxy-l,3-bis(trifluoro methyl )benzene 3.14 4-Ethoxy-l,3-bis(trifluoro methyl )benzene 2.99 4-Propoxy-l,3-bis(trifluoro methyl )benzene 2.99 4-Isopropoxy-l,3-bis(trifluoro methyl; benzene 2.99 4-Phenoxy-l ,3-bis (trifluoro methyl) benzene 3.09 (a)
Hunter, E. G. E. and Partington, J. R. , J. Chem. Boo.
z - 1232» 312.
(d) (e) (f) (g) (h) (i)
droves, L. G-. and Sugden, S., J. Chem. Boo. > 1957. 158. Wiswall, R. H. , Jr. and Smyth, 0. P. , J. Ghem. Phys. 2, 356 (1941). Roberts, MoElhill and Armstrong, ref. 9Malatesta and Pizzotti, ref. 10. Frieser, Hobbs and dross, ref. 11 Moore and Hobbs, ref. 12 Solution method das method
Moments” by 0. P. Smyth, Interspience Publishers, Inc. , New York, 1949• 8.
Sidgwick, N. W., Trans. Farad. Soc., JO, Appendix 1 (1934).
(ethoxy, etc.) were assumed to exhibit the same angle to the plane of the benzene ring as that for the methoxy group?. Aliphatic Nitro Compounds.— The dipole moments for nitroethane and 1-nitropropane are in satisfactory agreement with values reported in the literature for solution methods. The observed moment for 2-nitroethane is slightly higher than the observed moment for the above two compounds.
observed moment for 1 ,1-dinit roethane almost equals the cal culated moment for the compound* Organic Silicon Compounds.— The observed dipole moment for trimethylphenylsilane is 0 .56 x 10"18 esu. and agrees very well with the value of 0.44 x 10“**-8 esu. reported by Roberts, MoElhill and Armstrong^. 9#
The observed moment for
Roberts, J. D., McElhill, E. A. and Armstrong, R. , J. Am. Chem. Soc., %1, 2923 (1949).
trimethylbenzylsilane is 0.80 x lO~^8 esu. which is compara tively close to the moment for the above compound.
The —18 observed moment for triethylphenylsilane is 0 .63 x 10” esu. in fair agreement with the value of 0;98 x 10”18 esu.
reported by Malatesta and Pizzotti"^.
The observed moment
Malatesta, L. and Pizzotti, R. , Gazz. chim. ital. , %2 491 (1942); %3, 143 (1943).
for 2-nitrophenyltrimethylsilane is 3# 67 x lO~^8 esu. which gives an estimated moment of 0.73 x lO”^^ esu. toward the benzene ring for the trimethylsilicon group.
In view of the
mutual inductance which probably exists between the two groups (ortho effect) the actual group moment is thought to be less than this.
The direction of the trimethylsilicon
group supports the conclusion of Roberts, McElhill and Arm9 strong that this group is electron releasing as opposed to the idea of Malatesta^ that the moment for the triethylsilicon group is directed away from the benzene ring.
evidence is inconclusive with respect to [email protected] conclusion of Roberts, McElhill and Armstrong^ that there is very little resonance in benzene compounds containing the trimethyl silicon group. Fluorine Derivatives of Benzene.— The observed moment for fluorobenzene is 1.50 x 1CT18 esu. in good agreement with the value of 1.47 x 10”
eeu. reported by Preiser, Hobbs
and Gross^- as well as with other values reported in the 11.
Preiser, H . , Hobbs, M. E. and Gross, P. M., J. Am. Chem. Soc., II, 111 (1949).
The observed moment for 4-fluorotoluene is 1.82
x 10"18 esu. , in fair agreement with the value of 2.01 x 10“^8
esu. determined by Moore and Hobbs 12.
using a gas method.
Moore, E. M. and Hobbs, M. E. , ibid. , 71, 411 (1949). Halogen Derivatives of Benzene with One or Two Tri-
fluoromethvl Prouns.— Many of these compounds have two or more substituted groups ortho to each other on the benzene ring.
The mutual inductance between these groups leads to
an observed dipole moment which is lower than the calculated moment.
The compounds in which this mutual inductance
effect is absent have observed moments which are greater than the corresponding calculated moments.
This type of
behavior, in which the observed moment is greater than the calculated moment, is usually attributed to resonance in the compound?. Pentafluoroethyl Derivatives of Benzene.— The observed dipole moments for these three compounds and one compound reported by Brown^ were analyzed by vector addition and by comparison with the dipole moments of corresponding trifluoromethyl compounds, when available.
The estimated group
moment on benzene for the pentafluoroethyl group is 2.65 ' x 10"18 esu. , i. e. , 0.11 x 10”18 esu. higher than the group moment for the trifluoromethyl group on benzene. Ether Derivatives of Benzene with One or Two Trlfluoromethyl Groups.— In calculating the moments for these compounds it was necessary to assume that the trifluoromethyl group is very strongly electron attracting, and consequently the effective moment of the ether group is assumed to be In the
direction which will give the maximum calculated moment for the compound.
In spite o* this latter assumption the oh-
served moments for all these compounds except two are con siderably higher than the calculated values, the discrepancy in three cases being 0.97 x 10-18 ©su. or greater. The value of the group moments in determining the cal culated dipole moments, for Table IV, are given in Table V. The accuracy of both the He de strand and the Guggenheim methods of calculating dipole moments seems to be very good with moments above 1.00 x 10”^
Both methods are sub
ject to relatively high percentage errors for compounds having small or zero moments.
The results obtained by the
two methods agree well with each other. In the Guggenheim equation only E and G are unknown for a solute in a specified solvent.
The value of G can be
determined to four significant figures regardless of the value of the dipole moment.
For compounds having a small
dipole moment E represents the difference between two relative ly large terms which are almost equal.
values for benzene at 25° into the Guggenheim equation and considering errors in E only, we have : A A* = 0.0900( 6 3 )
and, since the square root of E appears in the denominator of the error expression, the relative error becomes larger with decreased values of E.
GROUP MOMENTS FOR CALCULATED DIPOLE MOMENTS Remarks
-00H 3 -
At 55° to the plane of the benzene ring
At 55° to the plane of the benzene ring
At 55° to the plane of the benzene ring
(053 )36 !-
Toward the benzene ring
Toward the benzene ring
Toward the benzene ring
As reported in this paper.
Weissberger, ref. 7 *
Brown, ref. 5 ;
Sidgwick, ref. 8 .
In the Hedestrand method of calculation the equation 1/2
(Pg08 - Fe)T
involves the difference between two large terms which are almost equal, Pg 0 0 a-nd Pe. A small error in either of these leads to a large error in
since at 25°C.
and the square root of (P200 - Pe) appears in the denominator of the error expression. The specified accuracy of the variable precision capacitor (General Radio 722-M) is ± 0.4 mmf.
Tests indicate that
the error in a given reading is ± 0.02 mmf. for the portion of the scale employed.
Since the difference between two
readings on the measuring cell and the difference between two readings on a comparison capacitor are used, the actual error is about 0.08 mmf.
This error is insignificant if
D/fg-is large (the dipole moment is large) but increases in importance as ÛD/f 2^decreases. One of the authors, Albert L. Myers, wishes to thank the Purdue Research Foundation for financial assistance in the form of a research fellowship. SUMMARY The dipole moments of four aliphatic nitro compounds, four organic silicon compounds, and thirty-two fluorine-
containing organic compounds were determined using a solution method and a heterodyne beat frequency oscillator.
Hedestrand equation was used to evaluate P200 * The LorentzLorenz equation was used to calculate the electronic polariza tion and the atomic polarization was assumed to be negligible* The dipole moments of twenty-eight of these compounds were calculated using an equation derived by Guggenheim. The results of the two methods of calculation were consistent with each other.
DETERMINATION OF DIPOLE MOMENTS OF SELECTED ORGANIC COMPOUNDS
INTRODUCTION Since the original paper by Debye (4) , a considerable amount of theoretical and experimental work has been done on the determination of dipole moments and their use in the study of molecular structure. The dipole moment of a sub stance is usually determined by measuring its dielectric properties in the gaseous phase or the dielectric and optical properties of a dilute solution of the substance in a non polar solvent. The behavior of the dielectric constant follows the equation of Debye (5); (I) p
- D ~ l D + 2
= 4irNa0 %
4-n-N/t 2 9kT
s total polarization
■ dielectric constant
s molecular weight
a Avogadro*s number
aQ « distortion polarizibility ytA m dipole moment k
a Boltzmann constant
s absolute temperature
This equation may also be written in the form
p . pe . pa„ . p0 . pe . pa- + 9kT
where Pe = electronic polarization Pa - atomic polarization P 0 = orientation polarization. If the value of the total polarization is determined at various temperatures, then we have (III)
P = a + b/T
a - Fe 4. Pa s
N aQ 3
b . uiMfc.2. The dipole moment of the substance under investigation can be calculated from the slope of the line obtained by plotting total polarization against the reciprocal of the absolute temperature•
There are limitations to using this approach
which will be discussed later. The equations which are given above work best when the molecules of the substance being investigated are far enough apart that they exert no appreciableeffect
This is the situation in gases and the dipolemoment
from the study of a substance in the gaseous phase is con sidered to be exact.
The dielectric constant and pressure
of the gas are determined for at least three temperatures over a range of 100°.
The total polarization at each tem
perature is calculated by Equation I and a plot is made of
polarization against the reciprocal of the absolute temper ature .
The slope of the line is determined and used in
Equation III to determine the dipole moment♦
mental difficulties of this method are relatively great.
dielectric constant must be determined with a high degree of precision (error
The pressures used should
be as low as possible to minimize the error introduced by deviations from the ideal gas laws.
The range of temperature
used will cause an expansion of the dielectric constant measuring cell and will change its capacity. If a substance whose dipole moment is to be investigated is dissolved in a nonpolar solvent then we can approach the situation prevailing in a gas since the solvent molecules separate the molecules of the solute to such an extent that the solute molecules exert practically no attractive force on one another.
In view of the experimental difficulty of
working with gases most of the determinations of dipole moments have been made in solution.
A pure liquid cannot
be used satisfactorily since the attractive forces between the molecules of a polar substance lead to a value for the total polarization which is lower than that found in dilute solution or in the gaseous phase (18). The method of plotting total polarization against temper ature, which is used for gases, is not particularly useful for solutions.
There is some interaction, usually inductive,
between the solvent and the solute which changes the dipole moment for any single temperature by a few per cent from the
correct value for ttie gas (6, 12, 18, 23) •
The amount of
Interaction changes with temperature, due to thermal agita tion of the liquid, and thus a serious error may be intro duced into the value for the slope of the plot of total polarization against temperature (b in Equation III).
for solutions the dipole moment is usually calculated from observations at a single temperature. The total polarization of a solution will be a function of the polarizations of the solute and the solvent.
equation for the relationship is (IV)
PX2 = D - 1 D + 2
Mlfl * M2fa a
_ plfl 4.P2f2
-■ total polarization of the solution D
= dielectric constant of the solution
■ molecular weight of the solvent
r molecular weight of the solute
- mole fraction of the solvent
s mole fraction of the solute
- density of the solution s polarization of the solvent
s polarization of thesolute
If the mole fraction of the solute is kept small (fq < 0.05) then the polarization of the solvent can be assumed to be constant. ^Ihe polarization of the solute may be constant, but ordinarily decreases with increasing concentration of the solute if the substance has a permanent dipole moment*
Thus an attempt is made to determine the polarization of the solute in the infinitely dilute solution by graphical or mathematical methods-
Graphical extrapolation is fre
quently difficult since the plot of polarization against concentration is usually curvedHede strand (ll) has shown that the extrapolation to zero concentration may be made mathematically if the di electric constant and density exhibit a linear dependence on the concentration.
Under these circumstances
D = Di (1 + kifg) cl » where
(X + kgfp ) and kg are constants = dielectric constant of solvent
d% = density of solvent This linearity usually exists (11, 19) and the Hedestrand equation has been used in the present investigation.
mathematical extrapolation is much more accurate than a graphical extrapolation. The total polarization of the solute in the infinitely dilute solution (Pgbo) is determined by the Hedestrand equation which is a limiting form of the Debye equation. The following derivation yields the Hedestrand equation in the form employed in this investigation. From Equation IV we can write the following expression for Pg
^2° — D — 1
D + 2
4" D - 1
’D * 2
- D% - 1 + 2
Rearranging and collecting terms Fp ~ D — 1
Mg '■ *■
D 4» 2
D - 1 D 4- 2
- Pi - 1 1_1 D% + 2 dx l
According to Hedestrand we may write for D, D - Dx (1 t ^ ,1*2)
and for d
d = d% (1 * "tpfg). Substituting for D and d, in the final term of the above expression % £ i n?id ♦ fgd [ D i d
»g = D - 1 % D 4- 2 d
- 1 2
(Dj - 1)(1 D-^ 4» 2
Rearranging and expanding P2 a 5zi D«-2
flMl n P i ^ D i f g - l ) (Di4-2) - (P1-l)(D1«-^>P1fg*2) d L fa CDi(i*%fa) *23 (Di-2)
ft.. (Pi-D [b%d+-4,f2) * # 1 XDÎd^fgTTTTn^^IaT" J
p2 = D-l D+2
^ fiM! d
3^Di --^JPi-1) [Did*4,f2) [pi(l*l,f2) * 2^
(Pi * 2)
w ï i © n fg--
O , fjL
, 940 cycles per second four fre quencies are produced:
100,000 cycles per second, 99»940
cycles per second, 199 >940 cycles per second and 60 cycles per second.
By the proper choice of circuit constants the
60 cycle beat can be amplified and compared with a standard 60 cycle frequency in a number of ways.
Figure 1(c) is a block diagram of a heterodyne beat apparatus.
0 % is a crystal controlled vacuum tube oscillator
operating at 100,000 cycles per second.
Q-g is a variable
oscillator which includes 100,000 cycles per second in its range.
0 is the measuring cell and Gs is a calibrated
M is the mixer where the outputs of the
two oscillators are mixed together.
A is an amplifier which
is connected to the indicating device (phones, oscillograph or other) for determining when the desired frequency is reached in the variable oscillator.
The tuning of G-g' can
be made very sharp for a 60 cycle difference between the two oscillators when an oscillograph is used as an indicating device and ordinary 60 cycle alternating current is used as
The difference between the readings on the
calibrated variable capacitor when the Measuring cell is empty and when it isfilled with sample plus a knowledge of the air capacitance of the cell are sufficient data for the calculation of the dielectric constant of the material in the cell. The heterodyne beat method is considered to be the most accurate of those used to measure the dielectric constant. The present investigation utilized this method in all work done.
As is indicated above, this method is not satisfactory
for solutions having an appreciable conductance.
measurements are reported for benzene solutions, low conduc tances are expected and the conductance effect is not con sidered important. EXPERIMENTAL Apparatus.— The apparatus used in this investigation was constructed and described by Paul E. Brown (2).
ing is a condensation of his description with minor changes where necessary to bring it up to date. The dielectric constant measuring cell has a cylindrical plate assembly consisting of three concentric cylindrical plateda.
The support for the plate assembly consists of a
length of 22 mm. Pyrex tubing sealed to a 34/45"Pyrex ground glass joint (ring seal, tubing extending through the joint). Two tungsten wires are sealed through the wall of the tubing to provide support and electrical connections for the plate
assembly (Figure 2):.
Copper wires soldered to the tungsten
wires inside the 22 mm. tubing provide external leads.
test tube bottom on the 22 mm. tubing completes the plate: assembly. The plate assembly container consists of a 34/45 Pyrex ground glass outer joint sealed to a length of 35 mm. Pyrex glass tubing. tubing.
A test tube bottom is blown on the 35 mm.
The length of this container is just sufficient to
admit the plate assembly and permit the 34/45 Pyrex ground glass joints to seat properly (Figure 2).
A length of 7 mm.
capillary tubing sealed to the bottom of the container joins the container and the mixing chamber (Figure 3) •
A side arm
of 8 mm. Pyrex tubing is sealed near the top of the container. Sheet nickel 0.47 mm. in thickness was used to ma&e three concentric cylinders having an average area of 61.2 sq. cm. The seams of the cylinders were "spot11 soldered with silver solder.
The inner and outer cylinders are 9 cm. in length,
while the middle cylinder is 8 cm. long.
The inner cylinder
and middle cylinder are spaced using six small pieces of Teflon as spacers.
The spacers are slightly more than 0.6
mm. in thickness and three spacers are placed at each end of the cylinders.
The inner and outer cylinders are joined by
two "U" shaped stirrups soldered at each end of the cylinders. These stirrups provide mechanical support and electrical connection between inner and outer cylinders.
soldered to the middle and outer cylinders are soldered to the tungsten leads in the wall of the 22 mm. Pyrex tubing.
z o CD
CO CO LU CL
cr m m o x 1 ° CD X
The inside of the 22 mm. tubing is packed with glass wool to prevent vibration of the copper wires leading from the tungsten wires to the top of the entire assembly. The plate assembly container and solution mixing cham ber are shown in Figure 3-
The mixing bulb is connected to
the bottom of the container by a length of 7 mm. Pyrex capillary tubing.
The 50 ml. mixing chamber is fitted at
the top with a 10/30 ground glass joint for insertion and \ removal of sample. A length of 8 mm. Pyrex glass tubing connects the top of the mixing bulb to 3^ a two-way stop cock.
Another two-way stopcock, Sg, is connected to the
plate assembly container just above the top of the plates by a length of 8
are connected as
shown and the two connections leading from
them are fitted with ball check-valves.
The two stopcocks
are connected to the "T" connection as shown and this con nection is joined to a 10 ml. hypodermic syringe.
piston of the syringe in and out serves to transfer the solu tion from the mixing bulb to the cell container and vice versa, depending upon the position of the two stopcocks. Si and Sg. The cell assembly container is encased in a metal water jacket extending
up to the bottom of the mixing bulb.
inlet and outlet
tubes are soldered in the side of the water
jacket near the bottom and the top of the jacket respective ly.
Water from a temperature-controlled water bath is si
phoned into the water jacket and the overflow through the
water jacket outlet is recycled to the water bath by a pump* Temperature control in the water bath is maintained by meansof a mercury thermoregulator which operates an electronic relay (110-volt, ÂG, gas tube operated).
A 100 watt lamp '
bulb is employed as a heater and a cooling coil is connected to the cold water tap of the laboratory water supply.
bath thus assembled will hold the temperature (in the 20-30° range) to within * 0.02°. The block diagram and chassis layout for the Heterodyne Beat Frequency Oscillator are shown in Figure 4.
Kc. Crystal Oscillator is the stable non-tunable oscillator. The Variable Oscillator is a modified Hartley circuit.
frequency is determined by the measuring cell and G-. R. 722-M, or by Gr. R. 848-BM and G-. R. 722-M depending on the position of the switch.
So the Variable Oscillator is always tuned
to 99>940 cycles per second when measurements are being taken.
The output from the Crystal Oscillator and the out
put from the Variable Oscillator are both fed to the grid of the Mixer stage.
In the Mixer stage "mixing" of the two
frequencies occurs and the resulting 60 cycle beat note is fed to the Amplifier stage.
From the Amplifier the 60 cycle
signal is fed to the vertical amplifier of the cathode ray oscillograph.
The cathode ray oscillograph is powered by
110-volt, 60 cycle current.
The horizontal amplifier of the
oscillograph is connected to the oscillograph test signal post.
This supplies 60 cycle voltage to the horizontal
amplifier and permits a comparison by Lis sajou pattern of the
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