Newman Projections Flashcards
Newman overview
- there is rotation about single bonds
- when looking down a given C-C bond, we can evaluate the amount of sterics present (penalizing/destabilizing energy introduced to the structure from the interaction of atoms/groups)
Sterics
- the relative energy associated with a given conformer or stereoisomer
- steric strain is the clashing of groups that are in close proximity ex. gauche interaction
Newman projections
used to represent compounds as viewed down a given C-C bond
circle = back carbon; goes away from your viewpoint aka the lines off the circle are the atoms/groups attached to the back carbon
front point = front carbon and at the forefront of your view; lines off the front point are atoms/groups attached to front carbon
when something exists in different steric states, it can exist in different __
conformations
steric repulsion between the electron clouds of atoms/groups raises a given conformation ____ in energy compared to a conformation with less steric interactions
higher
what conformation usually predominates and why
the staggered (anti) conformation because it is the most stable/lowest in energy - sigma donation (hyperconjugation) from a C-H bond will be donated inductively into the adjacent carbon's sigma orbital and this helps stabilize the staggered conformation
what is the highest energy conformation
eclipsed
newman projections will look different as drawn but they are the ___ molecule
SAME
staggered conformations
= atoms/groups are NOT eclipsing
- the angle between groups will be either 60, 120 or 80
3 distinct anti-relationships in a staggered conformation are:
Anti 1 - the groups in the plane of the page are anti to one another
Anti 2 - the solid wedge group is anti to the dashed wedged group on the adjacent carbon
Anti 3 - the dashed wedged group is anti to the solid wedged group on the adjacent carbon
Eclipsed conformations
- atoms/groups are eclipsing and their electron clouds are interacting (quite destabilizing)
- no anti-relationship exists in eclipsed conformations
- steric repulsion between the electron clouds of atoms/groups raises a given conformation higher in energy compared to a conformation with less steric interactions
The most stable eclipsed conformation will be the conformation with the ____ penalizing eclipsed interaction
least
The most stable staggered conformation is the conformation with the ___ penalizing gauche interactions
least
what is a gauche interaction
60 degrees apart aka next to each other in a staggered conformation
list out the “steric chart” from least steric penalty to most steric penalty
H < I < Br < Cl < OH < CH3 < CH2CH3 < CH(CH3)2 < C(CH3)3
halogen explanation: the larger the atom, the longer the bond and therefore the further away/removed from the steric interaction
