Calculations of induced moments in large molecules. The average polarisability and second hyperpolarisability of some polyacetylenes and a scale of polarisation for CH3, F, H and NH2. A comparative study

Abstract

The average polarisability, α, and second hyperpolarisability, γ, of H₂(C₂)_n, where n= 1–8, are reported. The dipole interaction theory has been invoked for the rationalisation of these results. The effective polarisabilities and hyperpolarisabilities of CH₃, F and NH₂ with respect to H have been investigated in some acetylene and diacetylene derivatives. The established order for the effective polarisabilities is F < H < NH₂ < CH₃, while F < H < CH₃ < NH₂ has been found for the effective second hyperpolarisabilities. The proposed relationships have been confirmed in a further series of molecules representative of substituted alkanes, alkenes and arenes. The computations have been performed by employing the CHF–PT–EB–CNDO method, the reliability of which is well established.