chapter4

chapter4 - What is the conflict today between energy and...

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1 What is the conflict today between energy and food?
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2 Worst Example of Cheating
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4. Organic Compounds: Cycloalkanes and their Stereochemistry Based on McMurry’s Organic Chemistry , 7 th edition
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4 We’ve discussed open-chained compounds up to this point Most organic compounds contain rings of carbon atoms e.g. - Prostaglandins - Steroids Cycloalkanes
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5 Why this chapter? Because cyclic molecules are commonly encountered in all classes of biomolecules : - Proteins (Amino Acids, Enzymes, Hair, etc.) - Lipids (Fats, Oils, Cell Walls, etc.) - Carbohydrates (Sugars, Starches, Cellulose) - Nucleic acids (DNA)
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6 4.1 Naming Cycloalkanes Cycloalkanes are saturated cyclic hydrocarbons Have the general formula (C n H 2n )
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7 Naming Cycloalkanes Find the parent. # of carbons in the ring. Number the substituents First Point of Difference 1,2,4 1,2,6 1,3,4
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8 4.2 Cis-Trans Isomerism in Cycloalkanes Cycloalkanes are less flexible than open-chain alkanes Much less conformational freedom in cycloalkanes (more rigid, less freedom of motion) Free Rotation about C-C bond No Rotation Possible about the C-C bond
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9 Because of their cyclic structure, cycloalkanes have 2 faces as viewed edge-on “top” face “bottom” face - Therefore, isomerism is possible in substituted cycloalkanes - There are two different 1,2-dimethyl-cyclopropane isomers Cis and Trans Isomers Possible
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10 Stereoisomerism Compounds which have their atoms connected in the same order but differ in 3-D orientation
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11 4.3 Stability of Cycloalkanes: Ring Strain Rings larger than 3 atoms are not flat Cyclic molecules can assume nonplanar conformations to minimize angle strain and torsional strain by ring-puckering Larger rings have many more possible conformations than smaller rings and are more difficult to analyze Most stable bond angle for tetrahedron is 109º How can a six membered ring be stable? Highly strained molecules.
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12 Stability of Cycloalkanes: The Baeyer Strain Theory Baeyer (1885): since carbon prefers to have bond angles of approximately 109°, ring sizes other than five and six may be too strained to exist Rings from 3 to 30 C’s do exist but are strained due to bond bending distortions and steric interactions Which ring structures are most commonly found in nature?
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13 Summary: Types of Strain Angle strain
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chapter4 - What is the conflict today between energy and...

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