Important things from Ch. 4 Flashcards
How do the properties of cycloalkanes differ from those of straight chain alkanes? Why?
Cycloalkanes have larger boiling points, melting points, and densities because they are more rigid in conformation with increased London dispersion forces
Why is it unfavorable to be planar?
All planar rings have high torsional strains
What is the A value?
Energy cost of being axial (unfavorable; table will be provided)
Ring strain is the strain associated with making a cyclic structure. It is a combination of which types of strain?
Bond-angle strain, torsional strain, and transannular strain
What is bond-angle 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
Bond-angle strain applies primarily to what?
Small rings
What is torsional strain?
Increase in energy due to eclipsing bonds; electron repulsion in eclipsing orbitals and unfavorable orbital overlap
What is transannular strain?
Strain from steric crowding of two groups across a ring (cannot be neighboring carbon substituents)
Transannular strain applies commonly to what?
Common or larger rings
List some properties of cyclopropane.
-planar conformation only
-high bond-angle strain (banana bonds)
-high torsional strain
List some properties of cyclobutane.
-exists as a puckered conformation to relieve a bit of torsional strain
-high-bond angle strain
-high torsional strain
List some properties of cyclopentane.
-exists as an envelope conformation
-low bond-angle strain
-low torsional strain (C-H bonds are staggered)
List some properties of cyclohexane.
-Exists as a chair conformation
-No bond-angle strain (chair has ideal bond angles of 109.5 degrees)
-No torsional strain (no eclipsing bonds)
Are substituted cyclohexanes strain free?
No, they have 1,3-diaxial interactions between axial groups on the same face of the ring
What is the planar bond angle of cyclopropane rings?
60 degrees
