Abstract.
Preferred signs of the dipole moment derivatives of the diacetylene have been determined by using G-sum rule graph and molecular orbital calculations. Atomic polar tensors and effective charges of the diacetylene are reported. The hydrogen effective charge calculated from the atomic polar tensor (x_H = 0.369e) is in excellent agreement with that obtained from G-sum rule graph (x_H = 0.371e). MNDO calculations on the H(CºC)_nH (n = 1, 2, 3, 4 and 5) series indicate that the hdyrogen effective charge increases with increasing number of CºC units. This is due to the magnitude of the dp_z /dz_H polar tensor element, as a consequence of the increasing charge flux along the series. Finally, this element seems to be a good indicator of t he instrinsic acidity of acetylenic protons.
 

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