Lab_3_Molecular_Models-3 - Lab #3 Molecular Models...

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Lab #3 Molecular Models Introduction The study of organic chemistry involves those molecules that contain carbon. Organic compounds are three-dimensional with a unique shape and occupy space. The molecular formula tells the number and type of atoms present in the compound, but it tells nothing about the true structure. The structural formula is a two-dimensional representation of the molecule and shows the bonding of the atoms. Structural formulas are frequently used because they can distinguish between isomers, compounds that share a common molecular formula but have different structural formulas. For instance, the molecular formula C4H10 can be represented by two different structures, butane and 2- methylpropane. They are therefore isomers. Consideration must be given to the shapes of molecules when considering stereochemistry, stable conformations, and steric interactions. Thus, we need a way to depict the three- dimensional shape of the molecules on a two-dimensional page. This is done using dashes and lines to represent bonds going behind the plane of the paper and bonds that come out of the plane of the paper, respectively. This is called a spatial representation and is a kind of structural formula. When investigating stable conformations, Newman projection formulas are useful. Newman projections provide a view along a carbon-carbon bond and depict the front carbon as a circle while the back carbon is hidden. Bonds that are attached to the front carbon are represented by
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lines coming from the center of the circle. Bonds coming from the back carbon are depicted by lines coming from the edge of the circle. With Newman projections, rotations show the spatial relationships of atoms and groups on adjacent carbon atoms easily. To learn how to draw spatial representations and Newman projections, molecular models are useful. These give a simple representation of the geometry of the molecules. Atoms are represented by different colored balls, and bonds are represented by sticks or tubes. Molecular models make the differentiation of different isomers and conformers much easier. Procedure
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This note was uploaded on 01/30/2011 for the course CHEMISTRY 120 taught by Professor Mcdavid during the Spring '10 term at American University of Science & Tech.

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Lab_3_Molecular_Models-3 - Lab #3 Molecular Models...

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