Electronic effects in X(CH2)nY homologous series by NMR and quantum chemistry

The 79,81Br NQR spectra of compounds of the Br(CH2) n COOH (n = 1-5) and Br(CH2) n COOSi·(CH3)3 (n = 1, 2, 4, 5) homologous series were measured at 77 K. The NQR frequencies of compounds of the first series as n increases to 3 and then oscillate. The 35Cl NQR frequencies of Cl(CH2) n Cl series molecules, estimated from the Cl3p populations resulting from RHF/6-31G(d) calculations, steadily decrease as n increases from 1 to 10. No oscillation of calculated 35Cl frequencies was revealed for compounds of the latter series (by contrast to experimental observations). The calculation results give no way to deducing the mechanism of the oscillation effect.