268
KURT hlOEDRITZER AND JOHN
R.
lnorga nz'c Claernistry
VAN WAZEK
calculations are summarized in Table IV. The total Calculation of the total number of geometrical isonumber of geometrical isomers of Nb2C12(C2H50)6- mers by considering the eight distinguishable ways to (C&"2, with the restrictions that (1) each niobium is distribute two pyridines on the eight nonbridging surrounded octahedrally by ligands, each niobium positions13 separately yields 123. This agrees with our preceding result is bonded to only one pyridine molecule, and ( 3 ) pyridine molecules cannot act as bridging ligands, is 70.
(13) T h e number eight was calculated from t h e cycle index for the D2h point group.
CONTRIBUTION FROM MONSANTO CHEMICAL COMPANY, CENTRAL RESEARCH DEPARTMENT, ST. LOUIS,MISSOURI
Scrambling of Methoxyl, Dimethylamino, and Chloro Groups on Silicon1 BY K U R T MOEDRITZER2
AND
JOHN Isphorus compound
kcal./ mole
P(OCHs)n(OCzH5)a $0.119 P( OCH,)( O C ~ H S ) 4-0 ~ 107
+0,052 - 3.82 P(OCzH5)2Clb -3.2 -4.72 P(OC2H,)C12 -3.2 -3.79 -7.8 P [N(C2H5)2]&IC -8 , 6 -9.1 P[X( C*Hb)a]C12 -9.0 -6.5 b Data from ref. 7. Data from ref. 8
In both the silicon and phosphorus cases, the rates of exchange are found to increase with the free energy of the exchange reaction. This is in agreement with the correlation of reaction rates which has been emphasized most recently by Hammond,12who states that "the most stable products are formed a t the most rapid rates from a series of similarly constituted reactants. " Acknowledgment.---We wish to thank hfessrs. Bruce E. Boggs and Richard A. K.uehne for the gas chromatography measurements. (11) C. A . Coulson, "Valence," 2nd Ed., Oxford, 1061, p . 221. (12) 6. S. Hammond, J . A m . Chenz. Soc., 77, 334 (1958). This correlation was first proposed b y Polanyi, see I,. P. H a m m e t t , "Physical Organic Chemistry," McGraw-Hill Book Co., New York, S . Y . , 1940.
