Effects of π bond type, backbone size, and halogen on structural and spectroscopic properties of hydrogen-bonded complexes of the X[BOND]H … π type between alkenes or alkynes and haloacids (HF and HCl)



The effects of CC bond type (double or triple), substituent (H or methyl), and halogen (F and Cl) on three properties of hydrogen-bonded complexes formed between unsaturated hydrocarbons and HX (X[TRIPLE BOND]F, Cl) are studied. The properties comprise hydrogen bond distances (RH), stabilization energies (SE), and frequency shifts (Δν). A 23 factorial design technique, along with ab initio (HF and MP2) and DFT (B3LYP and PBE1PBE) calculations, has been employed. All three responses are mainly affected by the halogen, and when it is changed from F to Cl, RH tends to increase, while SE tends to decrease. Surprisingly, the type of substituent is more important than the type of CC bond, for all three responses. Both effects tend to decrease RH. Significant interaction effects are obtained for the type of CC bond along with the type of substituent, and for the type of substituent along with the type of halogen. Both interaction effects are smaller than the main effects and also tend to decrease RH. The greatest SE values are obtained with PBE1 functional (BSSE + ZPE corrected values). Again, the next more important effect is due to the type of substituent, and the replacement of H by CH3 group tends to increase SE. The effect due to the CC bond type is not significant, at all computational levels. The only interaction effect that is significant for SE (corrected) and Δν is between factors 1 (CC bond type) and 2 (substituent), but only at HF and B3LYP levels, and it tends to increase both properties. As the halogen changes from F to Cl, Δν tends to decrease. In contrast, changing the substituent from H to CH3 leads to greater values of Δν. The effect of CC bond type is not significant at HF level, and when it is changed from double to triple Δν is decreased, at B3LYP and PBE1 levels. A suggestion as to how the results may point toward a better experimental detection of similar (π-type) complexes is also given. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006