The molecular structure of 1,3,5,7‐cyclooctatetraene has been studied by a sector‐microphotometer technique using data extending to very much larger scattering angles than were obtained in earlier investigations. An application of the method of least squares to sector‐microphotometer data in electron diffraction worked out by one of us (KH) has led in three refinement stages to unusually precise values for the parameters. The following are the more interesting parameter values with standard errors. It should be noted these results do not include a possible error of up to 0.2% in the scale of the molecule because of uncertainties in the electron wavelength, nor do they include the effect of correlations among the observations on the standard errors, which we estimate might increase the standard errors by as much as the factor 2^{½}. Molecular symmetry $D2d,C=C=1.334\xb10.001\u2009A,C\u2013C=1.462\xb10.001\u2009A,C\u2013H=1.090\xb10.005\u2009A,\u2220C=C\u2013C=126.46\u2218\xb10.23\u2218,\u2220C=C\u2013H=118.3\u2218\xb15.9\u2218,aC=C(=\u3008\delta l2\u3009C=C/2)=(103\xb17)\xd710\u22125,aC\u2013C=(147\xb110)\xd710\u22125,aC1\xb7\xb7\xb7C3=(256\xb113)\xd710\u22125,\u2009aC1\xb7\xb7\xb7C4=(530\xb1100)\xd710\u22125,\u2009aC\u2013H=(327\xb136)\xd710\u22125,\u2009aC2\xb7\xb7\xb7H=(520\xb1110)\xd710\u22125,aC3\xb7\xb7\xb7H=(640\xb1180)\xd710\u22125$.

## REFERENCES

*k*. In general the calculated function could be made to fit the middle parts of the curves fairly well, but began to deviate in the direction of greater density over the inner and lesser density over the outer parts of the curves. The

*f*curves of

*r*values accurate to 0.001 A. The calculations were carried out with a desk calculating machine: due to the range of our data the punch‐card methods were inapplicable.

*n*is the number of parameters being adjusted; hence structures having more than four parameters (the $D2d$ model of cyclooctatetraene has a dozen or more important geometrical and vibration parameters) are seldom thoroughly investigated.

*Introduction to the Theory of Probability and Statistics*(John Wiley and Sons, Inc., New York, 1950), Chap. 12.

*s*value reached in Hedberg and Schomaker’s experiment was 33, in Karle’s 22.