Vol. 85
COMMIJNICATIONS TO THE EDITOR
404fj
path of the internal conversion process. Since the favored conformation of I ,3-butadiene a t room t r r r perature is trans and since the singlet excited state is too short-lixred to permit rotations, the bicyclobutane can wine only from the trans molt=cules and the cyclobutene only from the czs molecules Thus we can write ,A&!.+~-
excited singlet
(CHz=CH= CH=CHa),
The predominance of cyclobutene over bicyclobutane in the products, in spite of the excess of the trans form of 1,3-butadiene in the reactants, may be due to the greater lability of the highly strained bicyclic compound. The present method offers a convenient synthesis of bicyclobutane. The efficiency of the process is improved by saturating a 1% solution of 1,3-butadiene in ether with cuprous chloride before photolysis.' On irradiation with 2537-A. light from a circular light sourceR for 4 days, 90yo of the butadiene had disappeared. The conversion to cyclobutene was 30y0 while the conversion to bicyclobutane was 5 to 6yG. The Cq fraction was separated from the solvent by fractional distillation and each component isomer was further separated by gas chromatography. The conversion to bicyclobutane in the only step of this method is about a third of that of the final photochemical step in the earlier r ~ i e t h o d . ~The , ~ present method may also be adaptable to the synthesis of certain derivatives of bicyclobutane.
three-dimensional Weissenberg photographic techniques, 1200 independent hkl intensity measurements were made with Mo K a radition. The correct interpretation of the three-dimensional Patterson function gave the positions of the Cu, 4 C1, and A1 atoms. The carbon atoms were located by three-dimensional Fourier methods. Full matrix anisotropic least-squares refinement was carried out to a final reliabilitv index, IZ1 = 21 IFo - F, 1 21 IF, , of 0.1;N.3 A final threedimensional difference map did not indicate any unusual features. The crystal structure is made up of infinite zigzagging sheets composed of tetrahedral Cu(1) and AIClq-. These sheets extend indefinitely normal *
. . CU
Cd& .
..
I
I
CIS
. . .. . . cu
cu
C~HG
to the ab plane and the interaction between sheets, in terms of interatomic distances, is only of van der Waals type. The Cu(1) ion is bonded to C1 atoms of three different -41C11- tetrahedr? with Cu-Cl bond ( 7 ) R. S r i n i v a s a n , J . . A m Chrni S o c , 86, 3048 (1963) (8) K S r i n i v a s a n , ibtd , 83, 4823 (1961) T h i s l i g h t source i s c o m m e r c i a l l y lengths of 2.36, 2.40, and 2.56 A. (distance expecJed available f r o m l h e S o u t h e r n K e w E n g l a n d Ultraviolet C o . , M i d d l e t o w n , from sum of normal covalent radii would be 2.34 A,). Cunn The benzene ring with Cu to center of nearest C-C ( ! I ) T h e conversion in ref 6 was calculated f r o m t h e s t a t e m e n t s t h a t t h e bond distance of 2.13 completes the coordination decomposition of t h e diazo c o m p o u n d t o yield nitrogen a n d CdHe was q u a n t i t a t i v e a n d t h a t t h e r a t i o of 1 , S - b u t a d i e n e t o bicyclobutane w a s .?: 1 T h e about the Cu(1) ion making i t four coordinate. The o v e r all yield f r u m allylacetic acid a p p e a r s t o be 2 6Tp geometry of the complex, bond lengths, bond angles, R. SRINIVASANand errors can be seen in Fig. 1. THOMAS J . LVATSON RESEARCHCENTER I S T E K S A T I O N A L BLTSINESS MACHINES CORP. In contrast to the C6H6. &&lo4 structure' where Y O R K T O l V N HEIGHTS, NElV \-OKK each Ag atom is bonded to two benzene rings forming RECEIVEDOCTOBER 21, 1963 an infinite chain of the type -C&-Ag-C&&-.%g.-. C6H6-,the c u ( I ) ion in C6H6.CU.klC14 is bonded uniquely to only one aromatic ring. In fact, in this case the Crysta1,and Molecular Structure of Metal Ion-Aromatic benzene rings are back to back with normal interComplexes. I. The Cuprous Ion-Benzene Complex, molecular distances. C&6' cLd1c1q The charge-transfer rationale5 for the nonexistence of the c6 symmetry Xg+.C& complex (Ag+ equiSir: distant from six carbon atoms) is t h a t the 5s acceptor We are carrying out a systematic investigation of orbital for A g + is not of the correct symmetry species chemistry, absorption spectra, and crystal structure to interact with the benzene e, molecular orbital under analyses of complexes of the type C& hf+''(Jllcld)x, cg symmetry. Further, the use of excited states of where Mi-" is a metal ion. We wish to report the Agf of the correct symmetry would involve 4 e.v. of results of a crystal structure determination of the excitation energy. The first of the above arguments C&. CuX1Cl4 complex. I This compound was prewould hold for a Cu(I).C6H6complex as well, but pared in an evacuated system from dry benzene and Cu(0) has a relatively low lying *D state, 1.5 e.v. anhydrous, resublimed cuprous and aluminum chlo above the ground state, and a CGcomplex might be rides. 2 Sing-lc crystals of the complex suitable for possible in this case. The results of the structure desingle-crystal X-ray diffraction were grown by removal termination show that this is not the case, and further, of benzene and transferred into thin-walled glass capilany theory t h a t neglects the role of the AlC14- entity laries which were subsequently sealed. is far too nai've. Solid C6H6 cu.qlc1, was found to crystallize with The AlC1'- ions presumably function as electron -1 formula units per unit cell in the monoclinic crystal donors as well as the aromatic ring to the Cu(1). system: ynit cell constants, n = 8.59, b = 21.511, The Al--Cl bond lengths are 2.13, 2.14, 2.15, and 2.07 (. z- (i.07 A , , p = ! K3'; space group Pel/n. By standard
a.
( II li I . Anima a n d R T u r n e r . A b s t r a c t s . 141th S a t i o n a l Meeting of t h e Anieric.tn ('hemica! Society. I os Angeles, Calif , A p r i l , 1 9 6 3 paper 30, P
12 I< (21 P r e p a r a t i o n , chemical, a n d physical properties will be reported in de-
tail a t a later d a t e
(3) [.east-squares calculations were performed with t h e Busing a n d Lev). O K I ~ 1 , S P r o g r a m a n d errors were calculated with t h e Busing a n d I x v y OKI'PE P r o g r a m on t h e I B M 7090 ( 4 ) H G S m i t h a n d R 13 R u n d l e , J . A m Chem. Sac., 8 0 , 5075 (1958) (5) R . S . Millliken, * b i d . , 64, 811 (1952).
Dec. 20, 1963
4047
COMMUNICATIONS TO THE EDITOR
2.39&0.006
;I
A.with the shortest AI-C1
associated with the non-Cu coordinated C1 atom. The A1-C1 distances observed in Co(A1C14)26varied from 2.11 t o 2.19 but here none of the C1 atoms could be considered as being coordinated to only an aluminum atom. Not only is the Cu(1) ion not placed on the benzene sixfold axis, but it is also not equidistant from the two nearest adjacent carbon atoms, 2.30 and 2.15 (distance expected from sum of covalent radii is 2.12 A.), A somewhat similar situation exists in C6H6. AgC104 (Ag-C, 2.49 and 2.63 but in this case the unequal metal to carbon distances manifest themselves in what appears to be a statistical disorder. The distortion of the benzene ring is toward a cyclohexatriene system with one of the short C-C bonds nearest the Cu(1). Although this ring distortion is just over the edge of statistical significance, it is worth noting that for C6H6.AgClO4 the C-C bonds closest to the metal ion were 1.354 and the others were 1.427 in length. In both these cases this bond shortening is opposite to what one might predict from simple MO or valence bond theory, and polarization forces may be the dominant factor in the bonding. To a first approximation the Cu(1) could be considered as tetrahedral with three chlorine and one benzene acting a s electron donors.
A.,
A.
Acknowledgment.-We wish t o acknowledge financial support from the National Science Foundation (G-15566). DEPARTMENT OF CHEMISTRY UNIVERSITY O F PITTSBURGH PITTSBURGH, PENNSYLVANIA 15213 RECEIVED OCTOBER3, 1963
The Polymerization of Bovine Pancreas Carboxypeptidase A'
A.),
a.
(6) J I Ibers. A d o C r y s f , 16,967 (1962)
A.
R . W. TURXER E. L. A M M A
Sir: Only two proteolytic enzymes, chymotrypsin2 and mercuripapain3 are known to form a rapidly equilibrating, polymerizing system in which double boundary formation, due to the presence of polymers higher than the dimer,4J can be observed in sedimentation experiments. This phenomenon has been observed only in low ionic strength buffers (,I1 = 0.09to 0 . 1 ) 2 , 3 , 6 ( 1 ) This work was carried o u t under N I H Grant Kumber HE07297
(2) V. Massey, W. F. Harrington, and R S Hartley, Discussi3ns F a r a d a y sot., ao, 24 ( I Q ~ . (3) E.I , . Smith, J . R . Kimmel, and D M Brown, J . R i d C h e i n . . 207, 533 (1954) ( 4 ) G . A . Gilbert, Discussions F a r a d a y Soc , 20, 68 (195.5). (5) G. A . Gilbert, P r o c R o y . SDC (Imndon), A260, 377 (1959) (6) I*. W. Nichol and J . I , , Bethune, .ValaI'e, 198, 880 (1963).
