organic exam 2

meso compounds

-have chiral centers -overall molecule is achiral -have internal plane of symmetry -not optically active --> don't rotate plane polarized light -each chiral center rotates light in opposite directions so overall the rotations cancel out

# of configurational isomers=

2^n n=# of stereocenters

nonsuperimposable

when mirror images of organic molecules cannot be completely matched

chiral

A molecule or carbon atom bonded to four different groups and without a plane of symmetry; thus, it is not superimposable upon its mirror image and has an enantiomer. no double bonds

anti conformation

A type of staggered conformation in which the two largest groups are antiperiplanar to each other; the most energetically favorable conformation

sterioisomer

Compounds with the same structural formula but with a different arrangement of the atoms in space.

conformational isomers

Stereoisomers that differ by rotation about one or more single bonds, usually represented using Newman projections.

torsional strain

Strain associated with adjacent bonds getting too close

steric strain

Strain associated with atoms "bumping" into each other

angle strain

Strain associated with improper bond angles

Two molecules that have the same molecular formula and connectivity but are nonsuperimposable mirror images of each other are related by being labeled as __________.

enantiomers

half-chair conformation

The unstable conformation halfway between the chair conformation and the boat conformation. Part of the ring is flat in the half-chair conformation.

gauche conformation

a conformation with a 60 degree dihedral angle between the largest groups

twist boat conformation

a nonplanar conformation of a cyclohexane ring that is twisted from and slightly more stable than a boat conformation

ring strain

arise from angle strain, torsional strian and nonbonded strain; multiplying strain by each CH2 group

A molecule and its chair flip are related by being labeled as __________.

conformational isomers

An eclipsed and a staggered Newman projection are related by being labeled as __________.

conformational isomers

constitutional isomers

differ in the order of attachment of atoms

Two molecules are not mirror images of each other. However, rotating the single bonds of one of the molecules such that it becomes a nonsuperimposable mirror image of the other molecule creates __________.

enantiomers

superimposable

identical in all respects. the three-dimensional positions of all atoms coincide when the molecules are placed on top of each other.

Cyclobutane adopts a nonplanar structure called the puckered conformation. Why does cyclobutane adopt the puckered conformation rather than a planar structure?

less torsional strain

chair conformation

most stable conformation of cyclohexane

envelope conformation (cyclopentane)

nonplanar; strain is minimized

pseudorotation

occurs by partial rotations about the C-C bond

constitutional isomers

same molecular formula, different connectivity

dihedral angle

the angle created by two intersecting planes

Newman projection

the nearer atom is depicted as a point, the further atom is depicted as a circle