Important things from Ch. 4

Cycloalkanes have larger boiling points, melting points, and densities because they are more rigid in conformation with increased London dispersion forces

All planar rings have high torsional strains

Energy cost of being axial (unfavorable; table will be provided)

Bond-angle strain, torsional strain, and transannular strain

Increase in energy associated with a bond angle that is decimated from the preferred angle of 109.5 degrees; orbitals distort (strain) to make rings w non-ideal bond angles

Small rings

Increase in energy due to eclipsing bonds; electron repulsion in eclipsing orbitals and unfavorable orbital overlap

Strain from steric crowding of two groups across a ring (cannot be neighboring carbon substituents)

Common or larger rings

-planar conformation only -high bond-angle strain (banana bonds) -high torsional strain

-exists as a puckered conformation to relieve a bit of torsional strain -high-bond angle strain -high torsional strain

-exists as an envelope conformation -low bond-angle strain -low torsional strain (C-H bonds are staggered)

-Exists as a chair conformation -No bond-angle strain (chair has ideal bond angles of 109.5 degrees) -No torsional strain (no eclipsing bonds)

No, they have 1,3-diaxial interactions between axial groups on the same face of the ring

60 degrees

90 degrees

108 degrees

120 degrees

129 degrees

28

26

6

0

6