Periodic trends in bond dissociation energies. A theoretical study.
Bond dissociation energies (BDEs) of all possible A-X single bonds involving the first- and second-row atoms, from Li to Cl, where the free valences are saturated by hydrogens, have been estimated through the use of the G3-theory and at the B3LYP/6-311+G(3df,2pd)//B3LYP/6-31G(2df,p) DFT level of theory. BDEs exhibit a periodical behavior. The A-X (A = Li, Be, B, Na, Mg, Al, and Si) BDEs show a steady increase along the first and the second row of the periodic table as a function of the atomic number Z(X). For A-X bonds involving electronegative atoms (A = C, N, O, F, P, S, and Cl) the bond energies achieve a maximum around Z(X) = 5. The same behavior is observed when BDEs are plotted against the electronegativity chi(X) of the atom X. Thus, for A-X bonds (A = Li, Be, B, Na, Mg, Al, Si), the BDEs for a fixed A increases, grosso modo, as the electronegativity differences between X and A increase, with some exceptions, which reflect the differences in the relaxation energies of the radicals produced upon the bond cleavage. A similar trend, albeit less pronounced, is found for single A-X bonds, where A = C, N, O, F, P, S, and Cl. However, there is an additional feature embodied in the enhancement of the strength of the A-boron bonds due to the ability of boron to act as a strong electron acceptor. The trends in bond lengths and charge densities at the bond critical points are in line with the aforementioned behavior.
Mó
Otilia
O
Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain.
Yáñez
Manuel
M
Eckert-Maksić
Mirjana
M
Maksić
Zvonimir B
ZB
Alkorta
Ibón
I
Elguero
José
J
D002627:Chemistry, Physical / Q000379:methods*; D004583:Electrons; D004602:Elements; D006859:Hydrogen / Q000737:chemistry; D008956:Models, Chemical; D008962:Models, Theoretical; D012984:Software; D013696:Temperature
D004602:Elements; D006859:Hydrogen