Organic chemistry

• Trans-trans geometry is more stable than cis-cis geometry
• Trans-trans geometry has a lower boiling point than cis-cis geometry because cis orientation has a higher dipole moment
• Dextrorotary isomers (D) rotate polarized light clockwise
• Levoratory isomers (L) rotate polarized light counterclockwise
• This is a Fisher projection of glucose in which horizontal lines are oriented out of the page (to HUG me) and vertical lines are oriented into the page

  
• Fisher projections are used to show 3D shape of a molecule
• This is a Newman's projection of glucose, which is the best to understand steric hindrance of particular sigma bond

  
• Ball and stick model of representation is the best to give information about relative size of atoms
• Enantiomers are stereoisomers that are non-superimposible mirror images
• Chiral center is a tetrahedral C (sp3 hybridized) that has 4 different groups
• Stereoisomers are isomers that differ in the 3-D arrangement of atoms
• Isomers are unique molecules that share the same molecular formula
• Structural isomers have the same molecular formula but different bond to bond connectivity
• Conformational isomers are not true isomers, but different spatial orientations of the same molecule
• Stereoisomers can be enantiomers or diastereomers
• Conformational isomers are best visualized by Newman's projections
• This is a conformation called

  A) anti-staggered

  
• These are 2 very different types of conformations

  A) staggered

  B) eclipsed

  C) 60

  
• Anti-staggered conformation is the most stable and has the lowest energy
• Eclipse conformation is the least stable and has the highest energy
• Eclipse conformation cause torsional strain or steric repulsions which in turn increase energy and reduce stability
• R arrangement means clockwise in enantiomers
• S arrangement means counter-clockwise in enantiomer
• R and S are considered absolute configurations
• to determine absolute configuration, we first assign priority based on atomic number, then move lowest priority away (dashed line) and check rotation for priority 1,2,3
• Relative configuration is when a chiral carbon of 2 molecules differs only by one substituent and others are absolutely identical in their orientation
• Enantiomers have identical boiling, melting, solubility, polarity
• Enantiomers are identified by the direction they rotate polarized light
• Dextrorotatory ia identified as + sign and rotate light to the right
• Levorotatory are identified with - sign and rotate light to the left
• This is hiw enantiomers rotate plane-polarized light

  A) polarizer

  B) polarimeter tubr

  C) analyzer

  D) observed rotation

  
• Two enantiomers will rotate the same plane-polarized light by the same magnitude but in opposite direction
• Two enantiomers mixed in equal concentration will produce racemic mixture with no plane-polarized light rotation
• Racemic mixture is separated by the reaction of enantiomers with another chiral molecule tp produce diastereomeric salts in the process called resolution
• The most common method used to separate enantiomers is chromatography
• Specific rotation is a standardized form of observed rotation, measured as observed rotation / concentration x length of polarimeter tube
• To calculate total number of stereoisomers, we use expression 2 to the power of n, where n is the number of chiral centers
• Diastereomers are stereisomers that are non-superimposible non-mirror images because they have oppositve configuration in some chiral centers
• If we have same groups attached to double bond, then we use cis or trans configuration
• If we have different groups attached to double bond, then we use E or Z configuration