ring strain in cycloalkane (+memorize structure)

Ring strain in C3-4 rings mainly from

angle strain, torsional strain

ie Cyclopropane (3), Cyclobutane (4)

Cyclopropane (3)

• eclipsed

• 60 degrees

• angle strain +torsional strain

Cyclobutane (4)

• staggered (mostly ig?

• 90 degrees

• angle strain +torsional strain

Cyclopentane (5)

• half eclipsed (c1-c2), half staggered (c5-c4)

• 110 degrees

• torsional strain

Ring strain in C5 rings mainly from

torsional strain

ie Cyclopentane (5)

Ring strain in C7-12 rings mainly from

Transannular strain (type of steric strain): steric clash between groups on opposite sides of the ring reaching into the same interior space

• spacious interior

+little angle strain as bond angles approach 109.5 degrees

+many bonds are partially staggered = moderate torsional strain

ie cyclodecane (medium ring)

Cyclohexane

• no angle strain or torsional strain (no ring strain)

• chair formation

  • all sp3

  • Newman projections along any C-C bond in the chair show perfectly staggered substituents — zero torsional strain.

• 
  

brief overview

Small ring (C3–C5):

• torsional → high

• angle → high

• steric → moderate

Medium ring (C6–C12):

• torsional → moderate

• angular → low/moderate

• transannular → significant

Large ring (C13+):

• torsional → low

• angular → low

• steric → increasing (folding interactions)