CHEM 2400 Lecture 5: SET 5

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CHEM 2400
Shanbhag Venkatesh

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SET 5 Starch and Cellulose 1. In starch, the O atoms joins two rings using one equatorial and one axial bond. 2. In cellulose, the O atom joins two rings using two equatorial bonds. Starch and cellulose are isomers. Indeed, stereoisomers. Just this minor difference in the 3D arrangment confers very different properties on starch and cellulose. Constitutional Isomers Differ in the way the atoms are connected to each other. They have different IUPAC names, the same or different functional groups; different physical properties; and different chemical properties. They have the same molecular formula though. Stereoisomers Differ only in the way atoms are oriented in space. Identifcal IUPAC names except for prefix like cis or trans. Same functional groups. Particular 3d arrangement is called a configuration. Chiral A molecule that is not superimposable on its mirror image. Ex. Human hand, CHBRClF Achiral Molecule that is superimposable on its mirror image. Ex. Socks, H20, Enantiomers Mirror images that are not superimposable. Tetrahedral stereogenic Center Carbon atom bonded to four different groups. Most chiral molecules contain one or more stereogenic centers. General principles regarding stereogenic centers 1. With no stereogenic centers a molecule generally is not chiral. 2. With one tetrahedral stereogenic center, a molecule is always chiral. 3. With two or more stereogenic centers, a molecule may or may not be chiral. Achiral molecules usually contain a plane of symmetry but chiral molecules do not, T or F? True. These C atoms cannot be tetrahedral stereogenic centers 1. CH and CH groups (more than one H bonded to C). 2. any sp or sp hybridized C (less than four groups around C). i.e. double or triple bond. ***Organic Molecules can contain two, three, or even hundreds of stereogenic centers. Any molecule with one tretrahedral stereogenic center is a chiral compound and exists as a pair of enantiomers. T Stereogenic Centers for Cyclic Compounds Find the possible stereogenic center (Not CH2 or CH3, or anything with a double or triple bond). Then compare the sides that the possible stereogeneic center is bonded to an figure out if the groups are different (i.e. a double or triple bond, other functional groups). Thalidomide
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