Organic Chemistry Chapter 2: Isomers Flashcards
What are structural isomers?
Share only a molecular formula. They have different physical and chemical properties.
What are conformational isomers?
They differ by rotation around a single sigma bond.
What are staggered conformations? anti staggered? gauche staggered?
have groups 60 degrees apart.
In anti-staggered, the two largest groups are 180 degrees apart, and strain is minimized.
In gauche, the two largest are 60 degrees apart.
What is an eclipsed conformation?
Have groups directly in front of each other. In totally eclipsed conformations, the two largest groups are directly in front of each other and the strain is maximized.
What are the three types of strain?
angle strain, torsional strain and non bonded strain
What is angle strain?
It is the stretching or compressing angles from their normal size, happens in cyclic molecules
What is torsional strain?
It is from eclipsing conformations
What is non bonded strain?
Happens because of interactions between substituents attached to nonadjacent carbons.
Which creates more non bonded strain - axial or equatorial?
axial
What are configurational isomers?
can only be interchanged by breaking and reforming bonds.
What are enantiomers?
Nonsuperimposable mirror images and thus have opposite stereochemistry at every chiral carbon. They have the same chemical and physical properties except for rotation of plane-polarized light and reactions in a chiral environment.
What is optical activity?
Refers to the ability of a molecule to rotate plane-polarized light d- or (+) molecules rotate light to the right; L- or (-) molecules rotate light to the left.
When are there chiral carbons, but no optical activity?
In racemic mixtures, when there are equal concentrations of two enantiomers, their rotations cancel each other out and there will be no optical activity.
Also Meso compounds - they have an internal plane of symmetry, so the two sides cancel each other out.
What are diastereomers?
non-mirror-image stereoisomers. They differ at some, but not all chiral center. They have different chemical and physical properties.
What are cis-trans isomers?
subtype of diastereomers in which groups differ in position about an immovable bond, such as a double bond or in a cycloalkane.
