lecture 9/10/11

where are large groups on chair form and why

equatorial because 1-3 diaxial interactions from big groups destabilize chair

how to use A-values

every 1.36 kcal/mol gives a 10x preference

sterochemistry configuration

is permanent aspects of spatial arrangement

constitutional isomers

same number and type of atoms but different bonding sequence

conformational isomers

related by a single bond rotational (ex staggered vs eclipsed)

configurational isomers

“permanent isomers” formed by breaking bonds

examples of configurational isomers

enautiomers, diastereomers, cis/trans, E/Z

achiral

having superimposable mirror images

elements of achiral molecules

occurs when either:

1. internal plane of symmetry

2. an inversion center (identical groups located equidistant from the center point)

chirality

lacking an internal symmetry element, cannot be perfectly superimposed

enautiomers occur when

stereocenter (an atom or point bearing groups such that interchanging any 2 result in a stereoisomer which is also called a configurational isomer)

what two centers are the same

stereocenter and chiral center

configurational isomer is the same as

stereoisomer

chiral center

an atom with 4 different groups

r vs s

stereocenters come in pairs and are ranked where R is priority

rules for r vs s

1. higher atomic number gets priority

2. first point of difference (in a tie, continue 2,3 bonds away until tie is broken

3. double bonds/triple bonds take priority because each bond counts as connected to another carbon

4. in a tie between isotopes, heavier wins

5. Z alkenes win over E

to assign R and S values

lowest priority group away from you and then R is clockwise and S is counterclockwise