Steric aspects in the fungicidal activity of O,O-bisaryl isopropyl phosphonates
1994
Nidiry, E.S.J. | Roy, N.K.
A comparative study of various steric parameters for O,O-bisaryl isopropyl phosphonate fungi-toxicants showed that a steric effect of substituents at the para position of the phenyl ring is best represented by molar refractivity, which shows that a bulk tolerance problem rather than a directional steric effect is involved. The relationship between fungitoxicity and molar refractivity of the para substituent is parabolic in nature. The steric effect of substituents at the meta position of the phenyl ring, which played a comparatively minor but statistically significant role in determining fungitoxicity to two fungi, is better represented by Taft's steric parameter or sterimol parameter for maximum width, which shows that this steric effect is directional in nature. The fitting of O,O-bisaryl isopropyl phosphonates through the para position of the phenyl ring into the cleft of the bioreceptor appears to be the crucial step in the mode of action.
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