NOTES
2876
2 75
255 Y 0
235
kJ!
c
215
al
a
E
!
195
I75 ,001 ,002 ,003
0
155 0
0.2
0.4
Mole
Fig. 3.-Solid--liquid
Fraction
0.6
0.8
1.0
p-Dioxane
phase diagram of p-dioxane-isopropyl chloride.
The eutectic and meritectic in the dioxane-methylene chloride system occur a t mole fractions of 0.029 and 0.258 and temperatures of 176.77 and 2O5.6O0K., respectively. The eutectic in the dioxane-isopropyl chloride system is a t 0.002 mole fraction dioxane and 155.88'K. A solid-phase transition occurring a t 272.8 A 0.3'K. was observed in all three systems and in pure dioxane. Because the conversion is slow, it ITas difficult to establish temperature equilibrium with time-temperature methods, making the uncertainty larger for this value than for the other measurements made in this study. Phase diagrams for dioxane-chloroform have been previously obtained by Kennard and McCusker5 and Rastogi and Girdhar.6 At temperatures above the upper eutectic, our data are in fairly good agreement with those of ref. 5 . At the lower temperatures, however, the temperature disagreement is considerable, our data being 4' higher at the lower eutectic. The general shapes of the two diagrams, however, agree fairly well. In describing their temperature measurements, Kennard and McCusker5 refer to an earlier paper in which they used a mercury-in-glass thermometer. Since approximately half of the measurements were made below the freezing point of mercury, however, some additional thermometer must also have been used. It is in this lower temperature range where the disagreement occurs. We discussed earlier in this paper the calibration of the thermometer that was used to obtain the data in Table I. (S) 8. A I . S. Kennard and P. A. IIcCuskor, J . Am. Chem. Soc., 70, 3375 (1948). (G) R. P. Rastogi and H. L. Giidhar, J . Chem. Eng. Data, 7, 176 (1962).
T'ol. 67
The discrepancies between the results of the present study and those of ref. 6 are even more pronounced in that the general shapes of the diagrams are quite different. The lower eutectic in the data of ref. 6 is displaced by 0.05 mole fraction unit to the right of where both ref. 5 and the present work locate it. Freezing points a t low mole fractions of dioxane are as much as 4 ' higher than this work and 8' higher than ref. 5 . Rastogi and GirdharBused a thermistor for a thermometer; they did not describe its calibration. A further difference among the results of the three studies on dioxane-chloroform is that Rastogi and Girdhare report an incongruently melting 1: 1 compound that was not found in the other two investigations. We took special care to obtain equilibrium in this region by alternate freezing and melting, slow cooling and slow warming, and maintaining the samples at the liquid nitrogen temperature for periods of 24 hr., but detected no evidence of a nieritectic halt. The upper eutectic was well defined all the way over to a mole fraction of 0.90 of dioxane. From this evidence me must conclude that if the 1: 1 compound does exist, either it must have a very low heat of formation or extensive supercooling prevented its formation in our apparatus. McGlashan and Rastogil quantitatively interpreted heat of mixing data for the dioxane-chloroform system in terms of H-bonding involving the hydrogen of CHC13 and the oxygens of dioxane. The three halogen compounds used in the present study also have the potential of H-bonding with dioxane. Of the three systems, all with halogenated molecules of somewhat similar geometry, only the dioxane-isopropyl chloride, the one in which the H-bond is predicted to be the weakest and which the freezing points show to be the most ideal, failed to form a compound. To this extent, the results reported in this paper are in qualitative agreement with the concept that H-bonding is the principal interaction in such systems. Since, however, CCl, also forms a compound with d i ~ x a n eit, ~is possible that even in CHCld and CH2C12,the bonding with dioxane could also involve the halogen directly. Acknowledgment.-The authors gratefully acknowledge the support given in this project by the National Science Foundation. PROTOK MAGNETIC RESQXANCE SPECTRA
OF DERIVATIVES OF p-PHEKYLISOBUTYROPHEXONE BY DER'NIS N.KEVILL~* AND SORMAN H. C R O M W E L L ~ ~ Auery Laboratory, Unisersity of Nebraska, Lincoln 8 , Nebraska Receined J u l y 26, 1966
The pertinent carbon atoms of p-phenylisobutyrophenone (I) have been classified as shown.
I
The p.m.r. spectra of derivatives formed by substi(1) (a) Chemistry Department, Northern Illinois University, DeRalb, Illinois; (b) t o nlioin communications concerning this paper sliould be addressed.
NOTES
Dec., 1963 tution of various groups on the a- and @-carbonatoms have been determined in methanol and carbon tetrachloride. Attention has been focused upon signals from @’and 7’-aromatic protons and upon signals from @methyl protons. (i) The two p’- and two 7’-protons formally coiistitute an A2B2 system. The system can, however, to a very close approximation be considered as two superimposed AB systems2 with a J A Bof 8 C.P.S. (ii) For substitution upon the or-carbon a signal corresponding to six equivalent methyl protons is observed. For substitution upon a @-carbon a signal corresponding to three methyl protons is observed, split by the a-proton with J A X = 7 C.P.S. Experimental The p.m.r. spectra were obtained with a Varian A-60 instrument using dilute carbon tetrachloride or methanol solutions containing a trace of tetramethylsilane ( 6 = 0.00) a internal reference. The compounds investigated were all analytical samples previously prepared in these Laboratories.314 The spectra of the protonated amines were obtained with the amines in the form of their hydrochlorides. The p-morpholino and p-piperidino derivatives are unstable oils, 3 and these p-amino ketones were prepared in situ b:y the addition of excess anhydrous sodium carbonate to methanolic solutions of the amine hydrochlorides.
Results The chemical shift (6) is expressed in parts per million displacement downfield from tetramethylsilane (6 = 0.00). The downfield changes in chemical shift (As) relative to the parent, p-phenyliso butyrophenone (I), are also expressed in parts per million (see Table I).
Discussion Wherever piossible, the p.m.r. spectra were determined in carbon tetrachloride so as to allow for facile comparison with other investigations. Since it mas desired to include measurements on amine hydrochlorides (insoluble in carbon tetrachloride), all compounds were also investigat,ed in methanol. The signals from methanol protons fall outside of the ranges in which the relevant solut,e signal positions occur. The chemical shift (6) usually varied only slightly with change of solvent froni carbon tetrachloride to methanol. The signal of the @-methyl protons of p-phenylisobutyrophenone (I) in carbon tetrachloride occurs at 1.226. This compares with a value for the methyl protons of propane of 0.90.6 Substitution of the aryl ketone group beta t o the methyl protons causes a change in cheinical shift of 0.326. I n carbon tetrachloride a-substituents -XHz, -OAc, and -Br result in changes in chemical shift (&) of the methyl protons of Ia very similar to, if not identical with, those reported by Jackman for substituents beta to methyl protons.6 An a-hydroxy group gives a change in chemical shift of 0.386 compared t o the predicted value of 0.2756. This anomalous shift is probably associated with the iiitramolecular hydrogen bonding known to exist in a-hydroxy ketones.’ h rupturing of (2) 1’. F. Cox, J . Am. Chem. Soc., 86,380 (1963). (3) N.11. Croniwell and P. H. Hess, %bid.,83, 1237 (1961). (4) D. N. Kevill and N. N.Cromwell, J . Org. Chem., i n pieas. ( 5 ) 1,. M. Jackman, “Applications of Nuclear Magnetic Resonance Specttoscopy In Organic Chemistry,” Peigamon Press, New Yolk, N. Y.,1959, p. 52. ( 6 ) Rcferenco 8, p. 53. (7) N. H. Croniwell and R. E. Barnbury, J . Ory. Chem., 26,997(1901).
2877 TABLE I
(Y-SUBSTITUTED DERIVATIVES OF p-PHENYLISOBTJTYROPHENONE
Ia Substituted group
X H
N
3
-Chemical
Change in cheinical shift, A s
1.2Za
shift, 8Y) (a) I n CCL-7.95 7.62
1.27
8.62
7.53
0.05
0.67
1.30
8.57
7.53
.OS
0.62
1.60 1.65 1.78 2.03
8.07 8.02 8.12 8.18
7.60 7.57 7.62 7.57
.38 .43 .56 .81
0.12 0.07 0.17 0.23
l.lSa
(b) I n CHaOH------8.00 7.70
..
..
1.30
8.65
7.68
0.12
0.66
1.35
8.60
7 68
.I7
.eo
-
.02
-
.03
P
---
P’
A@
A@’
A?‘
..
..
..
n
N S O LJ
OH OAc ON02
Br
*A f-7
N s O U
-0.09
-
-
.09 .02 ,05 00 .05
.
.. -0.02
OH
1.54
8.24
7.67
.36
.24
OAc
1.71
8.09
7.71
.53
.09
.01
ON02
1.80
8.15
7.75
.62
.I5
.05
1.88
8.04
7.81
.70
.04
*
1.89
8.06
7.81
.71
.06
.11
2.04
8.21
7.73
.86
.21
.Ol
H 3 i
+n
o
nN s
U
Br
11
&SUBSTITUTED DERIVATIVES OF ~PHENYLISOBUTYROPHENO~YE
lb Substituted group
X
-Chemicrtl shift, 6P 0’ Y‘
(a) I n CCh--7.95 7.62 7.93 7.59
Changein chemical shift, A9 A@ A0 ’ AY’
_ I
H Br
1.22‘ 1.29
7
..
..
..
0.07
-0.02
-0.03
..
.. 0.04
(b) I n CHaOH-------
I _ _ _ _ _
H G T O W
.lSb
8.00
7.70
..
.18
8.08
7.74
0.00
0.08
.19
8.08
7.77
.01
.08
.07
.29
8.05
7.77
.I1
.05
.07
.31
8.18
7.83
.13
.18
.I3
1.36
8.17
7.83
.16
.17
.13
C.P.S.
Signal corresponds to
a Split by a-proton, J A x = 7 six protons.
this hydrogen bondiiig may also accouiit for the small dccrease in AB for the a-hydroxy ketone in going from carbon tetrachloride to methanol; as olvent change
2878
Vol. 67
NOTES
which leads to a small increase in A@ for other I a compounds. The changes in chemical shift (A@’) of the @’-aromatic protons in I a compounds are unrelated to the corresponding A@-values. a-Substituents -0Ac
STABILITY CONSTANTS AND STRUCTURES OF SOME METAL COMPLEXES WITH Iil/lIDAZQLE DERIVATIVES’” BYA. CHAKRAYORTY A N D F. A. COTTON Department of Chemistry. Massachusetts Institute of Technology, Cambvidge 59, Massachusetts Received J u l y 88,1883
and H
-N
6
n 0
@U
possess large AB-values but, have only small A@’values. a-Substituents -OXO2 and -Br are iiiterniediate in character and have A@‘-valuesabout one quarter of their A@-values. At the other extreme, a-substituents
Recently the structure of the bis-(histidin0)-zinc(I1) molecule has been revealed by single crystal X-ray studies on (Z-CsH8N202)2 Zn * 2H202a and (dZ-CaH&aOz)zZn.5H20.2b I n these molecules, the histidino anions are coordinated primarily through the tertiary imidazole nitrogen and a-amino nitrogen forming stable sixmembered rings-the four nitrogens forming a distorted tetrahedral array about the zinc ion. The two carboxyl oxygens approach the zinc closely enough (2.8-2.9 A,) to be considered as loosely coordinated (I).
-*TJ
I1 I
and
JH2Y-
HN-NH
I11
have very small A@-valuesbut appreciable AB’-.c.alues, these large A@’-values being reduced aImost to zero upon protonation of the nitrogen. The a-hydroxy ketone shows further anomalous behavior in that with change of solvent, from carbon tetrachloride to methanol, the A@’-valueincreases from 0.12 to 0.246. In I b compounds, the @-substituents do not cause large changes in chemical shift of any of the three types of protons under consideration. @-Substituents of the + type -TU”R2 lead to quite appreciable A@’-values,larger than the Ab’-values for @-substituents of type -XRz. This constitutes a marked reversal of their relative effects when a-substituted. All @-substituted compounds investigated had changes in chemical shift of the y’-aromatic protons (Ay’) comparable to the changes in chemical shift of the @‘-aroniatic protons (A@’), and the Ay’-values were in all instances larger than the AT’-values obtained when the substituent was on the a-carbon. The changes in chemical shift of methyl protons within the substituted alkyl grouping can be predicted with good accuracy despite the group being contained within a fairly complex molecule. On the other hand, within the same molecule, the magnitude of long-range effects upon aromatic protons, several carbon atoms removed from the substituent, is dependent upon the molecular geometry rather than the number of separating carbon atoms. The magnitudes of the long-range effects bear no siniple relationship to the magnitudes of the changes in chemical shift of the methyl protons within the substituted alkyl grouping. Acknowledgment.-This work was supported in part by Grant No. 20,149 from the National Science Foundation.
m
HN-N
IV
In view of this result, it would be interesting to determine the trend of stability constants of the complexes of Zn(I1) with a series of ligands related to histidine, vix., histamine (11), @-(4-imidazolyl)-propionicacid (111, abbreviated henceforth as IPA), and imidazole (IT.’). Thus a decrease in stability in going from histidine to histamine (11) complexes might be correlated, a t least partially, with carboxyl coordination (I). A large decrease is anticipated in passing from complexes of I1 to thoqe of 111, due to the absence of the strongly coordinatiiig -NH2 group in I11 and the increased size of the chelate ring. Lastly, should there be a decrease in stability between complexes of I11 and those of IV, it might be presumed to reflect the measurable coordinating ability of carboxyl oxygen. With these points in mind, the present measurements of the stability constants of complexes of the four ligands mentioned above were undertaken. Apart from Zii(II), Cu(I1) and Ni(I1) systems were also studied to see if the same stability order is manifested, thereby indicating (but not proving) the occurrence of structural variations similar to those in the Zn(I1) case. It is to be recognized that the structure of bis-(histidino)-zinc(I1) molecule in aqueous solution may be different from what it is in the crystal, e.g., the weakly coordinating carboxyl oxygens might be displaced by mater molecules giving a more nearly regular octahedral structure. Experimental &Histidine and histamine were chromatographically pure samples. IPA was prepared from histidine hydrochloridea as white crystals, n1.p. 207” dec. (lit., 206-208” dec.). (1) (a) Financial s q p o r t for this work was provided by t h e Sational Institutes of Health. (2) (a) R. Kretzinger, F. A. Cotton, and E. F. Bryan, Acta Ciyst., 16, G5l (1953); (b) M. M. Harding and S. J. Cole, ibid., 16, 643 (1963).
