Lacey_Che131_F2011_Lect-34

Lacey_Che131_F2011_Lect-34 - Lec-34 Organic Chemistry Roy A...

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Lec-34: Organic Chemistry Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 1 Dipole-dipole Interactions Hydrogen bonds are responsible for: – Protein Structure • Protein folding is a consequence of H-bonding. • DNA Transport of Genetic Information Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 2
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Dipole-dipole Interactions H 2 O Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 3 Interactions involving non-polar molecules Dispersion forces (London forces) are intermolecular Dispersion forces (London forces) are intermolecular forces caused by the presence of temporary dipoles in molecules. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 4
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Interactions involving non-polar molecules ` The strength of dispersion forces depends on the polarizability of the atoms or molecules involved molecules involved. ` Polarizability describes the relative ease Polarizability describes the relative ease with which an electron cloud is distorted by an external charge. ` Larger atoms or molecules are generally more polarizable than small atoms or more polarizable than small atoms or molecules. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 5 Interactions involving non-polar molecules M l M d B ili P i t f C S i Molar Mass and Boiling Points of Common Species. Halogen M(g/mol) Bp(K) Noble Gas M(g/mol) Bp(K) He 2 4 F 2 38 85 Ne 20 27 Cl 2 71 239 Ar 40 87 Br 2 160 332 Kr 84 120 I 2 254 457 Xe 131 165 Rn 211 211 Boiling points increase with molar mass and polarizability Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 6
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Interactions involving non-polar molecules Hydrocarbon Alcohol Molecular Molar Bp Molecular Molar Bp Formula Mass ( o C) Formula Mass ( o C) CH 4 16.04 -161.5 CH 3 CH 3 30.07 -88 CH 3 OH 32.04 64.5 CH 3 CH 2 CH 3 44.09 -42 CH 3 CH 2 OH 46.07 78.5 CH 3 CH(CH)CH 3 58.12 -11.7 CH 3 CH(OH)CH 3 60.09 82 CH CH CH CH 58 12 0 5 CH CH CH OH 60 09 97 CH 3 CH 2 CH 2 CH 3 58.12 -0.5 CH 3 CH 2 CH 2 OH 60.09 Larger atoms or molecules are generally more polarizable than small atoms or molecules. Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 7 Na O < NaI < C H OH < C H A. Na 2 O < NaI < C 2 H 5 OH < C 3 H 8 B. C 3 H 8 < C 2 H 5 OH< NaI < Na 2 O C. NaI < Na 2 O < C 3 H 8 < C 2 H 5 OH OH D.
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