Lecture 5 - Organic Lecture Series CH 310/318 M LECTURE 5 Textbook Assignment Chapter 2 Todays Topics Alkanes conformations cyclic structures

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Organic Lecture Series 1 CH 310/318 M LECTURE 5 Textbook Assignment: Chapter 2 Today’s Topics: Alkanes; conformations; cyclic structures Alkanes; conformations; cyclic structures Notice & Announcements: Problem Set 1 posted- Due: 9/12; 3 PM Organic Lecture Series 2 Alkanes and Alkanes and Cycloalkanes Cycloalkanes Chapter 2 Chapter 2
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Organic Lecture Series 3 Conformations Conformations Conformation: Conformation: Any three- dimensional arrangement of atoms in a molecule that results from rotation about a single bond. Organic Lecture Series 4 • Staggered conformation: Staggered conformation: A conformation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from the atoms or groups on an adjacent carbon. • Newman projection: Newman projection: A way to view a molecule by looking along a carbon-carbon single bond. H HH H Conformations
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Organic Lecture Series 5 • Eclipsed conformation: Eclipsed conformation: A conformation about a carbon-carbon single bond in which the atoms or groups of atoms on one carbon are as close as possible to the atoms or groups of atoms on an adjacent carbon. H HH H H H Conformations Conformations Organic Lecture Series 6 • Torsional Torsional strain strain – strain that arises when nonbonded atoms separated by three bonds are forced from a staggered conformation to an eclipsed conformation. – also called eclipsed interaction strain eclipsed interaction strain. – the torsional strain between eclipsed and staggered ethane is approximately 12.6 kJ (3.0 kcal)/mol. +12.6 kJ/mol Conformations
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Organic Lecture Series 7 • Dihedral angle Dihedral angle Θ (Greek theta): The angle created by two intersecting planes. Conformations Conformations Organic Lecture Series 8 Figure 2.8 The energy of ethane as a function of dihedral angle. Conformations
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Organic Lecture Series 9 • The origin of torsional strain in ethane: – Originally thought to be caused by repulsion between eclipsed hydrogen nuclei. – Alternatively, caused by repulsion between electron clouds of eclipsed C-H bonds. – Theoretical molecular orbital calculations suggest that the energy difference is not caused by destabilization of the eclipsed conformation but rather by stabilization of the staggered conformation.
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This note was uploaded on 10/20/2011 for the course CH 310 M taught by Professor Iverson during the Fall '09 term at University of Texas at Austin.

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Lecture 5 - Organic Lecture Series CH 310/318 M LECTURE 5 Textbook Assignment Chapter 2 Todays Topics Alkanes conformations cyclic structures

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