Chapter 3 (conformations and cis-trans stereoisomers) Flashcards
the shape of a molecule with respect to bond rotations and other “easy” processes is called it’s
conformation
staggered conformation
each C-H bond bisects an H-C-H, and is preferred for reactions
eclipsed conformation
each C-H bond is aligned with an adjacent C-H bond
torsion or dihedral angle
the angle between two bonds in a conformation
types:
- eclipsed = 0°
- gauche = 60°
- anti = 180°
eclipsed conformers are ____ stable, whereas staggered conformers are ____ stable
least, most
the vast majority of molecules are in a ____ conformation at any given time
staggered
for conformers of large alkanes, in general, the ___-_____ conformer is most stable
all-anti
the most stable cycloalkanes should have internal bond angles near
109.5°
cyclopropane possesses severe ___ ____ and stuffers from _____ ____ because of its internal C-C-C bond angle of only 60°
angle strain; torsional strain
in cyclohexanes, to achieve 109.5° bond angle and minimize torsional strain, it adopts a ____ conformation, where all adjacent C-H bonds are staggered
chair
the chair conformer is the ____ stable for cyclohexane, but the boat (eclipsing C-H bonds) and skew-boat are considerably higher in energy than the chair conformer
most
in cyclohexane chairs, axial hydrogens are ____ to one another
anti
in cyclohexane chairs, equatorial hydrogens are ____ to one another
gauche
“right-leaning” and “left-leaning” chair conformers can inter invert rapidly via ____ _____ or chair flip
ring inversion, where the axial groups become equatorial and vice versa, but substituents remain the same
in mono substituted cyclohexanes, the substituted group in the ____ conformation is preferred (more stable) because the van der Waals strain between hydrogens is negligible
equatorial
stereoisomers
have the same formula and connectivity, but different positions of groups in space (cis isomer, trans isomer)
trans isomer is ___ stable compared to the cis
more, because cis isomer contains destabilizing van der Waals interactions
the ___, ________ conformer is most stable for disubstituted cyclohexane conformers
trans, diequatorial
in disubstituted cyclohexanes with two different substituents, the more stable chair is the one with the larger group _______
equatorial
polycyclic ring systems
contain 2+ rings, are classified according to the number or rings, and are equal to the minimum number of bond disconnections necessary to generate a completely acyclic structure
spiro polycyclic ring classification
two rings share 1 carbon in common
bridged polycyclic ring classification
two rings share 3+ carbons in common
fused polycyclic ring classification
two rings share 2 carbons in common
heterocycles
rings containing 1+ heteroatoms
