Addendum Chapter 4
63
3. M. Birk, R.R. Freidl, E.A. Cohen, H.M. Pickett and S.P. Sander, J. Chem. Phys. 91,
6588 (1989).
4. N.C. Baird and K.F. Taylor, J. Chem. Phys., 72, 6529 (1980).
5. B.R. De and A.B. Sannigrahi, Int. J. Quantum Chem., 19, 485 (1981).
6. G. Mamantov, E.J. Vasini, M.C. Moulton, D.G. Vickroy and T. Maekawa, J. Chem.
Phys., 54, 3419 (1971).
7. J.R. Morton, K.F. Preston and S.J. Strach, J. Chem. Phys., 69, 1392 (1978).
8. T. Kiang and R.N. Zare, J. Amer. Chem. Soc., 102, 4024 (1980).
9. N.C. Baird, J. Chem. Educ., 54, 291 (1977).
10. N.C. Baird, Pure and Appl. Chem., 49, 223 (1977).
Addendum Chapter 4
1. Charge-shift Bonding
Covalent-ionic resonance (A•─•A ↔
(-) A׃ A
(+) ↔
(+) A ׃A
(-) ) pertains for the
electron-pair single bonds of H 2 and F 2 . For H 2 , but not
11 for F 2 , the covalent
structure alone is stable relative to the separated atoms (cf. Table 3-1 for H 2 ).
Charge-shift bonding
11 via covalent-ionic resonance is needed to bind F 2 relative
to the dissociation products F + F.
2. Quadruple Bonding
Quadruple bonding have been calculated to occur in C 2
12,13 and analogous eightvalence electron species CN
+
, BN and CB
- 13 . In Ref.
14 , it is deduced that an (S = 1
spin) triple bonding might occur in B 2 , in preference to the single bond that is
associated with the molecular orbital configuration in Table 4 1. To help describe
a quadruple bond for C 2 , it is noted that for the eight valence-shell electrons, we
may write:
{(2s)
2 - (2s)
2 }{(p)
2 - (p)
2 }{( x
)
2 - (
*
x
)
2 }{( y
)
2 - (
*
y
)
2 }
(1)
{2s a .2s b + 2s b .2s a }{ za . zb + zb . za }{ xa . xb + xb . xa }{ ya . yb + yb . ya }
(2)
Each of these equations gives a (non-variational) linear combination of 16
Slater determinants. Only one of the 16 MO configurations involves four doublyoccupied bonding MOs. There is also one MO configuration in which the four
antibonding MOs are doubly-occupied.
To allow for 2s-2pmixing, with the 2p z AOs oriented so that the AO overlap
integral < za | zb > is greater than zero, the 2s and z AOs are replaced by the
hybrid AOs of Eqn. (3),
63
3. M. Birk, R.R. Freidl, E.A. Cohen, H.M. Pickett and S.P. Sander, J. Chem. Phys. 91,
6588 (1989).
4. N.C. Baird and K.F. Taylor, J. Chem. Phys., 72, 6529 (1980).
5. B.R. De and A.B. Sannigrahi, Int. J. Quantum Chem., 19, 485 (1981).
6. G. Mamantov, E.J. Vasini, M.C. Moulton, D.G. Vickroy and T. Maekawa, J. Chem.
Phys., 54, 3419 (1971).
7. J.R. Morton, K.F. Preston and S.J. Strach, J. Chem. Phys., 69, 1392 (1978).
8. T. Kiang and R.N. Zare, J. Amer. Chem. Soc., 102, 4024 (1980).
9. N.C. Baird, J. Chem. Educ., 54, 291 (1977).
10. N.C. Baird, Pure and Appl. Chem., 49, 223 (1977).
Addendum Chapter 4
1. Charge-shift Bonding
Covalent-ionic resonance (A•─•A ↔
(-) A׃ A
(+) ↔
(+) A ׃A
(-) ) pertains for the
electron-pair single bonds of H 2 and F 2 . For H 2 , but not
11 for F 2 , the covalent
structure alone is stable relative to the separated atoms (cf. Table 3-1 for H 2 ).
Charge-shift bonding
11 via covalent-ionic resonance is needed to bind F 2 relative
to the dissociation products F + F.
2. Quadruple Bonding
Quadruple bonding have been calculated to occur in C 2
12,13 and analogous eightvalence electron species CN
+
, BN and CB
- 13 . In Ref.
14 , it is deduced that an (S = 1
spin) triple bonding might occur in B 2 , in preference to the single bond that is
associated with the molecular orbital configuration in Table 4 1. To help describe
a quadruple bond for C 2 , it is noted that for the eight valence-shell electrons, we
may write:
{(2s)
2 - (2s)
2 }{(p)
2 - (p)
2 }{( x
)
2 - (
*
x
)
2 }{( y
)
2 - (
*
y
)
2 }
(1)
{2s a .2s b + 2s b .2s a }{ za . zb + zb . za }{ xa . xb + xb . xa }{ ya . yb + yb . ya }
(2)
Each of these equations gives a (non-variational) linear combination of 16
Slater determinants. Only one of the 16 MO configurations involves four doublyoccupied bonding MOs. There is also one MO configuration in which the four
antibonding MOs are doubly-occupied.
To allow for 2s-2pmixing, with the 2p z AOs oriented so that the AO overlap
integral < za | zb > is greater than zero, the 2s and z AOs are replaced by the
hybrid AOs of Eqn. (3),