mod 4 ch 4 Flashcards
define angle strain
the strain induced in a molecule when bond angles are forced to deviate from the ideal 109 tetrahedral value
define tortional strain
the strain induced by the eclipsing of bonds
what is the problem with cyclopropane conformation
it cannot do anything to relieve the angle and tortional strain its experiencing
what is the problem with cyclobutane conformation and how does it fix this
- its has less angle strain than cyclopropane (90) but it has more tortional strain due to 8 eclipsing C-H bonds
- it relieves this strain by ring puckering
what is the problem with cyclopentane conformation and how does it fix this
- its has almost no angle strain (108) but it has more tortional strain due to 10 eclipsing C-H bonds
- it relieves this strain by ring puckering
what are the ring puckering conformations of cyclohexane from the most strained to the least
most strained - half chair
boat
twist boat
least strained - chair
why is the chair conformation of cyclohexane the most stable
it has no angle or tortional strain
what occurs in a ring flip
- all carbons shift one position clockwise
- axial bonds become equatorial bonds and equatorial bonds become axial bonds
- bonds that were pointing up are still pointing up
- bonds that were pointing down are still pointing down
when choosing which chair conformation is the most stable…
it is always the one with the largest group in the equatorial position
what are the two kinds of steric strain in chair conformations? define them.
- 1,3-diaxial interaction - strain between two big groups axially or between a big group and a hydrogen
- gauche - between two big groups on adjacent carbons either both equatorial or axial/equatorial
when drawing chair conformations from reg conformations
wedge is _____ and dash is _____
wedge is UP and dash is DOWN
