Conformational Analysis Flashcards
(24 cards)
conformations
different spatial arrangements of a molecules that are generated by rotation about single bonds
- torsional strain
destabilization that results from eclipsed bonds
van der Waals strain
destabilization that results from the atoms being too close
most stable conformation:
staggered/anti
least stable conformation:
eclipsed/syn
angle/ring strain
strain that results from distortion of bond angles from the normal value of 109.5 degrees
least and most stable cycloalkane
least stable: cyclopropane
most stable: cyclohexane
strains present in cyclopropane
torsional strain and angle strain
strains present in cyclobutane
usually exists in puckered conformation: reduced torsional strain, angle strain
conformations available for cyclopentane
envelope conformation and half chair conformation
strains present in conformations for cyclopentane
more reduced torsional strain, angle strain
are cycloalkanes planar?
NO
most extreme conformations in cyclohexane
chair (MOST STABLE, no torsional strain, ring strain and 1,3-diaxial repulsions) and boat (flagpole interactions, eclipsing torsional strain, ring strain)
what types of positions are atoms are bonded in chair conformation?
axial and equatorial
flagpole interactions are a subclass of:
van der Waals strain
ring flipping of cyclohexane causes:
axial bonds becoming equatorial and vice versa
the most stable conformations is chair with the largest substituent bonded:
in equatorial position (reduces crowding and 1,3-diaxial repulsion, as well as gauche interaction with the ring)
if there is no large substituent on chair cyclohexane (hydrogens only), the ratio of conformations exists in:
50/50
for tert-butyl substituent, it is fixed so that:
it is in equatorial position (very big/bulky)
the more sterically demanding/bulky the substituent,
the more it prefers the equatorial position
cis/trans refers to:
configuration
axial/equatorial refers to:
conformation
the more stable configuration (cis/trans) of disubstituted cyclohexanes depends on:
the conformations available, favours both equatorial axis
to determine which material reacts fastest by an elimination mechanism:
determine which molecule spends more time in its reactive conformation (consider halogen regioselectivity for periplanar hydrogens)
