Organic Chemistry Chapter 4: Isomers I

Conformer

A nonsuperimpossable molecule that have the same connectivity but differ by roation about single bond

Rotational Conformation

The distinct angle of rotation about a single bond

Newman Projection

2D representation of a molecule viewed down the bond of interest

Dihedral Angle 

The angle between a bond on the front atom and a bond on rear atom of a newman projection, each angle of rotation defines a particular dihedral angle 

Eclipsed Conformation

A rotational geometry in which bonds to fronnt atom in a newman projection eclipse the bonds to the rear atom

Staggered conformation

A geometry in which each single bond on front carbon atom in newman projection bisects a pair of single bonds on the rear atom

Torsional strain

An increase in energy that appears in eclipsed conformation

Rotational Energy Barrier:

The amount of aenergy needed to convert one conformer into another by rotation about a specific bond

Steric Strian 

An increase energy that results from electron repulsion between atoms or groups of atoms that are not directly bonded together but occupy same space

Anti conformation

bulky groups that are 180 degree apart in newman projection

Gauche conformation

Bulk groups that are 60 degree apart in newman projection

All-Anti (Zigzag) Conformation

Lowest energy conformation of an alkyl chai, has anti conformation at each c-c bond

Isomer

A molecular species that has the same formula as another molecular species but is different in some way 

How does guache and anit affect energy

gauche raises energy, anti doesn’t

Why is eclisped energy higher

the bonds are overlapping

How does steric strain increase 

with size of groups increasing

Ring Strain

The increase in energy due to geometric constraints of the bonds and substituents invovled in a ring 

Angle Strain 

An increase in energy that arises when actual bond angles differ significantly from ideal bond angles

Chair Conformation

A cyclohexane geometry in which all bond angles of the ring are 111 degree and all C-C staggered

Envelope conformation

The lowest energy geometry of cyclopentane, four of its five carbon atoms are essentially in one plane where the fifth is outside the plane