lecture 17 (ch 8) - Organic Lecture Series CH 310/318 M...

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Organic Lecture Series 1 CH 310/318 M LECTURE 17 Textbook Assignment: Chapter 8- Cont’d Today’s Topics: Haloalkanes Haloalkanes -the free radical reaction the free radical reaction Notice & Announcements: Exam II: Grading in Progress Organic Lecture Series 2 Haloalkanes Haloalkanes Chapter 8 Chapter 8
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Organic Lecture Series 3 • Haloalkanes are associated in the liquid state by van der Waals forces. • van van der der Waals forces: Waals forces: A group intermolecular attractive forces including: – dipole-dipole forces. – dipole-induced dipole forces. – induced dipole-induced dipole (dispersion) forces. • van der Waals forces pull molecules together. – As molecules are brought closer and closer, van der Waals attractive forces are overcome by repulsive forces between electron clouds of adjacent atoms or molecules Van Van der der Waals Forces Waals Forces Organic Lecture Series 4 – The energy minimum is where the attractive and repulsive forces are balanced. – Nonbonded interatomic and intermolecular distances at these minima can be measured by x-ray crystallography and each atom and group of atoms can be assigned a van van der der Waals radius Waals radius. – Nonbonded atoms in a molecule cannot approach each other closer than the sum of their van der Waals radii without causing nonbonded interaction strain. HF C l B r C H 2 CH 3 I Increasing van der Waals radius (pm) 120 135 180 195 200 200 215 Van Van der der Waals Forces Waals Forces
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Organic Lecture Series 5 • For an alkane and a haloalkane of comparable size and shape, the haloalkane has the higher boiling point. –The difference is due almost entirely to the greater polarizability of the three unshared pairs of electrons on halogen compared with the low polarizability of shared electron pairs of covalent bonds.
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lecture 17 (ch 8) - Organic Lecture Series CH 310/318 M...

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