The electron diffraction method of investigation has been used to determine the nature of the potential barrier restricting the rotation about the carbonhyphen;carbon single bond in ethylene chloride (CH2Clsngbnd;CH2Cl). Assuming that the shape of the barrier is given by a cosine function, the height of the barrier is between 5 kcal./mole and infinity. This potential barrier is compared with the barrier resulting from the exchange repulsions and the electrostatic repulsions of the two ends of the molecule. Eyring's method was used for calculating the exchange repulsions. The repulsions between the chlorine atoms must be calculated differently from the repulsions between hydrogen and chlorine atoms in order to obtain agreement between theory and experiment. Duplicate experiments were done at Princeton and at Pasadena.
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