RHF and MP2 ab initio molecular orbital calculations using the 4-31G** and 6-311G** basis sets have been employed to obtain Green's function matrix elements (G(D,A)) and intermolecular charge transfers (DeltaQ(corr)) of the CnNH (...) CnNH and CnNH (...) NCnH (n = I and 3) hydrogen bonded complexes. Our calculations reveal that these two parameters are linearly correlated. Their values increase by effect of the addition of a C-2 group to the proton donor and/or acceptor and when the hydrogen bonding is formed by the NH (...) C skeleton in comparison to the NH (...) N one. Our calculations have also revealed that the corresponding increments in G(D,A) and DeltaQ(corr) due to change from NCH (...) NCH to CNH (...) NCH or from NCH CNH to CNH CNH are very similar. Finally, both G(D,A) and AQ(corr) show the same behavior when the hydrogen bonding distance is progressively increased from the equilibrium position until 4.5 Angstrom, forming two exponential curves practically superposed. Correlations between DeltaE and DeltaQ(corr) as well as DeltaE and G(D,A) are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.