Organic Chemistry Ch 2. Isomers Flashcards
Structural isomers
Share only a molecular formula, have different chemical and physical properties
Confirmational isomers
Differ by rotation around a single sigma bond
Staggered confirmations
Have groups of 60° apart as seen in a Newman projection
Anti staggered molecules
The two largest groups are 180° apart
Gauche staggered molecules
The two largest groups are 60° apart
Eclipsed confirmations
Have groups directly in front of each other as seen in a Newman projection
Totally eclipsed confirmation
Two largest groups are directly in front of each other and strain is maximized
Angle strain
Created by stretching or compressing angles from their normal size, creates a strain in cyclic molecules
Torsional strain
Created from the clips and confirmations, also creates a strain in cyclic molecules
Non-bonded strain
Interactions between substituents attached to nonadjacent carbons, also creates a strain in cyclic molecules
Cyclic molecule strain
Angle strain, torsional strain, and non-bonded strain, cyclic molecules will usually adopt non-planer shapes to minimize the strain
Axial substituents
Substituents attached to cyclohexane that are sticking up and down from the plane of the molecule, create more non bonded strain
Equatorial substituents
Substituents attached to cyclohexane in the plane of the molecule, typically where the largest substituents are
Configurational isomers
Can only be interchanged by breaking in reforming bonds
Enantiomers
Non-superimposable mirror images unless have opposite stereo chemistry at every chiral carbon, have the same chemical and physical properties except for rotation of plane polarized light and reactions in a chiral environment
Optical activity
Refers to the ability of a molecule to rotate plane polarized light, D or plus molecules rotate light to the right and L or minus molecules rotate light to the left
Racemic mixtures
If equal concentrations of an ant hammers will not be optically active because the two enantiomers rotations cancel each other out
Meso compounds
Have an internal plane of symmetry and also will be optically in active because the two sides of the molecule cancel each other out
Diastereoisomers
Are non-mirror image stereoisomers, they differ at some but not all chiral centers, have different chemical and physical properties
Cis trans isomers
Or some type of diastereoisomers in which groups differ in position about an immovable bond such as a double bond or a cyclo alkane
Chiral centers
Have four different groups attached to the center carbon
Relative configuration
Is the stereo chemistry of a compound in comparison to another molecule
Absolute configuration
What is the stereo chemistry of a compound without having to compare it to other molecules, uses the Cahn-Ingold-Prelog priority rules
Cahn-Ingold-Prelog Priority rules
Priorities given by looking at the atoms connected to the chiraol carbon or double bonded carbon, which ever has the highest atomic number gets highest priority, if there’s a tie one moves outward from the chiral carbon double bond until the tire is broken
Z alkene
Occurs at the highest priority substituents are on the same side of the double bond
E alkene
Occurs is the highest priority substituents are on the opposite sides of the double bond
Determining stereo centers configuration
Putting the lot lowest priority group in the back and drawing a circle from 1 to 2 to 3 and descending priority
R stereocenter
If circle is counterclockwise
S stereocenter
If circle is clockwise
Fischer diagrams
Vertical lines go into the page of the plane (dashes), horizontal lines come out of the plane of the page (wedges), switching one pair of substituents in a fisher diagram inverts the stereo chemistry of the chiral center, switching to pairs retains the stereo chemistry, rotating 90° inverts the stereo chemistry of the chiral center, rotating 180° retains the stereo chemistry
