Org Chem Lec M5

• Isomers are compounds having the same numbers and kinds of atoms but differ in the way the atoms are arranged
• Types of Isomers

  • structural (or constitutional) isomers
  • stereoisomers
• Types of Stereoisomers

  • conformers (rotamers)
  • configurational isomers
• structural or (constitutional isomers) has different bond pattern
• stereoisomers has the same bond pattern
• conformers (rotamers) is interconvertible by single bond rotation
• configurational isomers is not interconvertible by bond rotation
• Types of Constitutional (Structural) Isomers

  • skeletal - different carbon skeletons
  • functional - different functional groups
  • positional - different position of functional groups
• Stereochemistry is the branch of chemistry concerned with the three-dimensional structures of molecules
• Stereoisomers has the same molecular formula and constitution but different spatial (3D) arrangement of atoms, same connectivity
• Geometric (Cis-Trans) Isomers

  • lack of rotation in C=C bonds
  • for disubstituted alkenes
• Stereochemistry

  chemistry concerned with 3D structures

  focus on chirality or handedness
• Chirality

  any object can be viewed in a mirror, revealing its mirror image
• Superimposable - the mirror image is identical to the actual object
• Nonsuperimposable - the object and its mirror image are different
• Plane of Symmetry

  • a plane that cuts through the middle of a molecule or other object so that one half of the object is a mirror image of the other half
  • a molecule is not chiral (achiral) if it contains a plane of symmetry
• Optical Activity

  ability to rotate a beam of plane-polarized light
• Polarimeter

  measures the amount of rotation
• Dextrorotatory (+)

  optically active molecules rotate plane-polarized light to the right (clockwise)
• Levorotatory (-)

  optically active molecules rotate plane-polarized light to the left (counterclockwise)
• Racemetes

  • known as racemic mixtures
  • 50:50 mixture of enantiomers
• Enantiomers

  stereoisomers that are nonsuperimposable mirror image
• Diastereomers

  stereoisomers that are NOT mirror images of each other
• Meso Compounds

  compounds that are achiral, yet contain stereocenters
• Chirality

  objects that are not superimposable on their mirror images are chiral objects
• Chirality Center

  the most common source of molecular chirality is the presence of a carbon atom bearing four different groups
• Enantiomers

  when a compound is chiral, it will have one nonsuperimposable mirror image, called its enantiomers