Previously, Haddon defined the p-orbital axis vector
(POAV) in order to measure the direction of the p-orbital at
each carbon atom in nonplanar alkenes (Figure 5). The p orbital
is assumed to make equal angles to the three σ bonds
in pyramidalized alkenes (10). In this work, the POAV was
located at each carbon atom of the double bond and then
used to measure the POAV torsion angle in order to quantify
the p-orbital misalignment angle (φ). φ values are included
in Figure 3 for the three illustrated dihedral angles of
150, 120, and 90 in twisted trans-2-butene. These misalignment
angles are slightly less than half the measured
CCCC dihedral angle differences from ideality. For example,
at a C1C2C3C4 dihedral angle of 150° without
pyramidalization, φ should be 30; the calculated
misalignment angle, however, is only 14.2. This retention
of p-orbital overlap (and hence, π-bond strength) as a result
of pyramidalization has been substantiated in earlier works
(10).
Previously, Haddon defined the p-orbital axis vector
(POAV) in order to measure the direction of the p-orbital at
each carbon atom in nonplanar alkenes (Figure 5). The p orbital
is assumed to make equal angles to the three σ bonds
in pyramidalized alkenes (10). In this work, the POAV was
located at each carbon atom of the double bond and then
used to measure the POAV torsion angle in order to quantify
the p-orbital misalignment angle (φ). φ values are included
in Figure 3 for the three illustrated dihedral angles of
150, 120, and 90 in twisted trans-2-butene. These misalignment
angles are slightly less than half the measured
CCCC dihedral angle differences from ideality. For example,
at a C1C2C3C4 dihedral angle of 150° without
pyramidalization, φ should be 30; the calculated
misalignment angle, however, is only 14.2. This retention
of p-orbital overlap (and hence, π-bond strength) as a result
of pyramidalization has been substantiated in earlier works
(10).
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