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CH 320M Chapter 3 Powerpoint Notes

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CH 320M
John A.Colapret

Chapter 3 Tuesday, September 03, 2013 11:17 PM Jean Baptiste Biot ---- in 1832, observed rotation of tartaric acid  Continued this research in 1847  Investigated shapes of ammonium sodium tartrate crystals o Found to be chiral  HE WAS THE FIRST TO PRODUCE A PURE SAMPLE OF LEVOTARTARIC ACID ISOMERS: Isomers - different compounds with the same molecular formula Constitutional isomers- isomers with a different connectivity Stereoisomers - isomers with the same connectivity but a different orientation of their atoms in space CHIRALITY: Chiral - greek word of cheir [hand]  An object that isn't superposable on its mirror image Achiral - an object that lacks chirality --- one that lacks handedness  An achiral object has at least one element of symmetry  Plane of symmetry - an imaginary plane passing through an object dividing it so that one half is the mirror image of the other half  Center of symmetry - a point so situated that identical components of the object are located on opposite sides and equidistant from that point along any axis passing through it STEREOCENTER: The most common (but not the only) cause of chirality in organic molecules is a tetrahedral atom [most commonly carbon] bonded to 4 different groups! Chiral center - a carbon with 4 different groups bonded to it  All chiral centers are STEREOCENTERS o But not all stereocenters are chiral centers Enantiomers - stereoisomers that are nonsuperposable mirror images  2-Butanol o o Has one stereocenter o 4 representations for one enantiomer  o 2 representations for the enantiomer of (4)  Refers to the relationship between pairs of objects! OTHER EXAMPLES OF ENANTIOMERS: 2-chlorobutane   3-chlorocyclohexene  R & S CONVENTION: Priority rules 1. Each atom bonded to the chiral center is assigned a priority based on ATOMIC NUMBER a. The higher the atomic #, the higher the PRIORITY b. 2. If priority can't be assigned per the atoms bonded to the chiral center, look to the next set of atoms a. Priority is assigned at the FIRST POINT OF DIFFERENCE b. 3. Atoms participating in a double or triple bond --- are considered to be bonded to an equivalent number of SIMILAR ATOMS BY SINGLE BONDS a. NAMING CHIRAL CENTERS: 1. Locate the chiral center and identify its four substituents 2. Assign priority from 1 (highest) to 4 (lowest) to each substituent 3. Orient the molecule so that the group of lowest priority (4) is directed away from you a. 4. Read the 3 groups projecting toward you in order from highest (1) to lowest priority (3) 5. If the groups are read clockwise, the configuration is R a. b. If they are read countercloc
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