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
