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December 23, 2010


hugh cartwright

Your statement that dimethyl ether has zero dipole moment is incorrect. The C-O-C bond angles at the oxygen are not 180 as shown in your diagram, but close to 110 degrees. Since the oxygen is far more electronegative than carbon there exists a bond dipole at each C-O bond, and since the two C-O bonds are not colinear vector addition shows there's a residual molecular dipole. In this molecule that dipole is of the order of 1.3 Debye.

John Dunn

You're right. The di-methyl ether's dipole moment is not zero (my slip) but it is very small. The dipole moment of ethyl alcohol is much greater. Please see Asimov's Guide to Science by Isaac Asimov, ISBN 0-465-00472-5, Copyright 1972, pages 478 and 486.

The key point however is that the trait of dipole moment that give rise to dielectrophoresis under the influence of an applied high voltage.

John Dunn

I've edited the above essay to reflect your comments, Hugh. Perhaps a sanity check would be in order though.

Thank you.

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