3691
activation4 and positive “r” hydration parameters’ previously observed, it appears t o be a bimolecular (A-2) process. In addition a unimolecular reaction involving methyl-oxygen cleavage would give the unlikely methyl carbonium ion. What is apparently occurring is an sN2 type of displacement on the methyl carbon of the protonated imidate, with a neutral amide as the leaving group. An analogous reaction has been
9,
1.500
0
Ph-C-N, 11
/
-+
H26-CH3
+ Ph-C-NC=O center. Cleavage of acetylacetone and condensation at the imine center of the starting complex was also indicated. A three-dimensional X-ray diffraction study of the dithionate salt has established that the complex cation has the structure shown in Figure 1. The crystals were monoclinic, space group Pzl/c, with a = 7.576 (4), b = 18.209 (7), c = 14.068 (6) A, /3 = 125.25 (2)”, and Z = 4. Reflection data were collected on a Picker FACS-I four-circle diffractometer using graphite-crystal monochromated Cu Kar radiation [ 1479 unique reflections with I/a(l) 2 3.01. Data have been corrected for absorption effects. Block-diagonal least-squares refineCommunications to the Editor
3692 Scheme I 0
The process generates a novel amino acid tridentate complex and an asymmetric center at the C atom where condensation occurs. Reactions of this type have value in their capacity to expand synthetic expertise in chelate chemistry and especially for the prospects they give in synthesizing multidentate complexes.
0
II I
CH CCHCCH, f NU
I
?+
B. T. Golding, J. MacB. Harrowfield, G . B. Robertson A. M. Sargeson,* P. 0. Whimp Research Scliool of ChemiJtry, Australiati National Unicersity Canberra, A.C.T., Airstralia 2600 Receiced February 4, I974
c
c
Optical Activity Associated with Isolated Olefinic Bonds. II. Experimental Evidence for the Role of a-Bond Torsion in Circular Dichroism Couplets and the Question of the us + rx* Contribution' Sir :
CH
In earlier studies of olefin circular dichroism we proposed the allylic bond polarization (ABP) model to account for the sign of the low energy portion of the couplet observed for most endocyclic olefins.'** In this we followed the suggestion of Scott and Wrixon3 ascribing the couplet to a,,* + rX -t ax* with ax-+ ax* representing the low energy portion. Levin and Hoffmann recently reported calculations of a -+ a * rotatory strengths of model olefins,4 suggesting that a-bond torsion sense is the dominant factor in the C D of twisted olefins. We now wish to present new data which constitutes: (1) support for the ry* ax -+ ax* assignment for cyclohexene C D couplets, (2) the first experimental evidence estab,lishing the characteristics of torsion induced olefin CD, and (3) the first observations suggesting an additional CD active transition in the region of the uv dominant a -t a * transitions. We consider this new band to be the (T, +. ax* transition previously placed in this energy span by various calculations.; The assignment of the C D couplet to the two a a*
-
-
(1) For part I see N. H. Andersen, C. R. Costin, D. D. Syrdal, and D. P. Svedberg, J . Amer. Chem. SOC.,95, 2049 (1973). (2) The ABP model1 and the Scott-Wrixon dissignate octant rule3are closely related. In the ABP model attention is focused on the chiral relationship of the more polarizable allyl bonds and the A orbital rather than the carbon framework as a whole. See W. I.9 On this basis we conclude that the rX 3s transition is not a major contributor to either band of the CD couplets observed. (7) A. W. Burgstahler, R. C. Barkhurst, and J. R. Gawronski in "Modern Methods of Steroid Analysis," E. Heftmann, Ed., Academic Press, New York, N. Y., 1973. The authors acknowledge the receipt of this manuscript prior to publication. (8) A. E. Drake and S. F. Mason, J . Chem. SOC.,Chem. Commuti., 253 (1973). (9) N. H . Andersen and Y . Ohta, submitted for publication.
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-f
-
Journal of t h e American Chemical S o c i e t y
/ 9 6 : l l 1 Muy 29, 1974
