12
1
General Principles
⊡ Figure 9
Part of the pseudorotational itinerary of cyclopentane
Substituents cause parts of the pseudorotational itinerary to become more populated to avoid
eclipsing and 1,3-diaxial interactions. In the envelope conformation, the ring atom out of the
plane has pseudoequatorial (12) and pseudoaxial positions (13) as do the atoms next to it that
partially avoid eclipsing interactions. Substituents on the remaining two atoms are eclipsed.
In the twist conformation, the atom on the C 2 axis has two identical isoclinal positions that
also partially avoid eclipsing interactions (14). Thus, the barrier to pseudorotation for methylcyclopentane, which corresponds to having the methyl group in the least stable site, is larger,
14.2 kJ mol −1 [88].
Microwave [90,91,92] and far-IR [93,94] spectra indicate that the barrier to pseudorotation
in tetrahydrofuran is small (0.8 to 2.0 kJ mol −1 ). Modeling the potential energy surface has
1
General Principles
⊡ Figure 9
Part of the pseudorotational itinerary of cyclopentane
Substituents cause parts of the pseudorotational itinerary to become more populated to avoid
eclipsing and 1,3-diaxial interactions. In the envelope conformation, the ring atom out of the
plane has pseudoequatorial (12) and pseudoaxial positions (13) as do the atoms next to it that
partially avoid eclipsing interactions. Substituents on the remaining two atoms are eclipsed.
In the twist conformation, the atom on the C 2 axis has two identical isoclinal positions that
also partially avoid eclipsing interactions (14). Thus, the barrier to pseudorotation for methylcyclopentane, which corresponds to having the methyl group in the least stable site, is larger,
14.2 kJ mol −1 [88].
Microwave [90,91,92] and far-IR [93,94] spectra indicate that the barrier to pseudorotation
in tetrahydrofuran is small (0.8 to 2.0 kJ mol −1 ). Modeling the potential energy surface has