Chapter 2- Isomers Flashcards
constitutional isomer
same molecular formula, but different structures
structural isomers
aka. constitutional isomers. only share molecular formula (same molecular weights)
- different chemical and physical properties due to different connectivity
physical properties
no change in composition of matter (ex: melting point, boiling point, solubility, odor, color, and density)
chemical properties
reactivity of the molecule with other molecules and result in changes in chemical composition. (generally dictated by functional groups)
stereoisomers
share same connectivity as each other, but their arrangement in space is different.
conformational isomers
differ in rotation around single bonds
configurational isomers
can be interconverted only by breaking and reforming bonds
2 categories (both optical isomers)
- enantiomers
- diastereomers
angle strain
torsional strain
nonbonded (steric strain)
AS- bond angles deviate from ideal values by being stretched or compressed
TS- results when cyclic molecules must assume conformations that have eclipsed or gauche interactions
NBS- van der Waals replusion, results when nonadjacent atoms or groups compete for the same space.
5 different cyclohexane conformations
puckered envelope chair* - most stable boat* twist-boat*
chair flip
when chair conformation flips and all axial become equatorial and vice versa. but all wedges remain wedges and all dashed lines stay dashed.
chirality
an object is considered CHIRAL if its mirror image cannot be superimposed on the original object. object lacks an internal plane of symmetry. (ex: hands)
ACHIRAL objects can be superimposed on their mirror images.
enantiomers
type of configurational isomer. nonsuperimposable mirror images.
- nearly identical physical and chemical properties
- rotate plane-polarized light in opposite directions and react differently in chiral environments.
diastereomers
type of configurational isomer. chiral molecules that share the same connectivity but are NOT mirror images of each other. (b/c they differ at some of their multiple chiral centers). also rotate plane-polarized light.
what does it mean to be optically active?
having the ability to rotate plan-polarized light. MUST have chiral center and lack a plane of symmetry
optical activity- refers to rotation of plane-polarized light by a chiral molecule.
d- or + to refer to clockwise rotation of polarized light
l- or - to refer to counter-clockwise rotation of polarized light
racemic mixture
solution with both + and - enantiomers in equal concentration. displays no optical activity.
