150
Chapter 11 Pauling “3-Electron Bonds” and “Increased-Valence” Structures
longer than single bonds; this they are found to be; see Table 11-3. (We have
assumed that the two equatorial bonds of SF 4 , with lengths of 1.54 Å are singlebonds; the standard Lewis structures, namely
and
, show this to
be the case.) On the other hand, the reported bond-lengths for H 2 S 2 and
3 2 2
(CH ) S
indicate that these molecules have S-S single bonds, with the hydrogen and methyl
radicals unable to stabilize the Pauling “3-electron bonds” of S 2 .
From “increased-valence” structure (34) for F 2 SO, we would predict that the SF bonds should be longer than the single-bond length of 1.54 Å, and that the S-O
length should be similar to that of free SO. Although lengthening of the S-F bonds
is observed, the S-O bond-length of 1.41 Å is shorter than the 1.48 Å for free SO.
Possibly this shortening is due to a significant contribution of “increased-valence”
structure (35) to resonance with (34); in structure (35), the S-O bond-number +
bond-order (maximum value = 2.5) exceeds the value of 2 that occurs in (31).
Similarly, for FSO, “increased-valence” structure (36) will participate in
resonance with “increased-valence” structure (37), from which it may be deduced
that the S-F and S-O bond-lengths for this radical are respectively longer than a
single bond, and shorter than that of free SO. The experimental lengths of 1.602
and 1.452 Å are in accord with this deduction.
The above theory is also appropriate for Cl 2 SO, whose S-Cl and S-O bondlengths of 2.077 Å and 1.443 Å are respectively longer than the S-Cl single-bond
length of 2.014 Å for CH 3 SCl, and shorter than that for free SO.
For HSO, a valence-bond structure similar to (36), with H replacing F, accounts
simultaneously for the observations that the S-O length of 1.494 Å is similar to the
1.481 Å for free SO, and that the S-H length of 1.389 Å is longer than the singlebond length of 1.336 Å for H 2 S. However, on the basis of the discussion in
Section 11-4 for HO 2 , it would be expected that the H-S bond length for HSO
would be similar to those for HS and H 2 S, and that the S-O bond-length would be
appreciably longer than that of free SO.
Chapter 11 Pauling “3-Electron Bonds” and “Increased-Valence” Structures
longer than single bonds; this they are found to be; see Table 11-3. (We have
assumed that the two equatorial bonds of SF 4 , with lengths of 1.54 Å are singlebonds; the standard Lewis structures, namely
and
, show this to
be the case.) On the other hand, the reported bond-lengths for H 2 S 2 and
3 2 2
(CH ) S
indicate that these molecules have S-S single bonds, with the hydrogen and methyl
radicals unable to stabilize the Pauling “3-electron bonds” of S 2 .
From “increased-valence” structure (34) for F 2 SO, we would predict that the SF bonds should be longer than the single-bond length of 1.54 Å, and that the S-O
length should be similar to that of free SO. Although lengthening of the S-F bonds
is observed, the S-O bond-length of 1.41 Å is shorter than the 1.48 Å for free SO.
Possibly this shortening is due to a significant contribution of “increased-valence”
structure (35) to resonance with (34); in structure (35), the S-O bond-number +
bond-order (maximum value = 2.5) exceeds the value of 2 that occurs in (31).
Similarly, for FSO, “increased-valence” structure (36) will participate in
resonance with “increased-valence” structure (37), from which it may be deduced
that the S-F and S-O bond-lengths for this radical are respectively longer than a
single bond, and shorter than that of free SO. The experimental lengths of 1.602
and 1.452 Å are in accord with this deduction.
The above theory is also appropriate for Cl 2 SO, whose S-Cl and S-O bondlengths of 2.077 Å and 1.443 Å are respectively longer than the S-Cl single-bond
length of 2.014 Å for CH 3 SCl, and shorter than that for free SO.
For HSO, a valence-bond structure similar to (36), with H replacing F, accounts
simultaneously for the observations that the S-O length of 1.494 Å is similar to the
1.481 Å for free SO, and that the S-H length of 1.389 Å is longer than the singlebond length of 1.336 Å for H 2 S. However, on the basis of the discussion in
Section 11-4 for HO 2 , it would be expected that the H-S bond length for HSO
would be similar to those for HS and H 2 S, and that the S-O bond-length would be
appreciably longer than that of free SO.