assignment 2 answers - CHM 1321A Assignment #2 Answers 1)...

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CHM 1321A Assignment #2 Answers 1) Diethyl ether and 1-butanol have similar solubilities in water, but their boiling points are very different. Explain why these compounds have similar solubility properties but different boiling points. O OH solubility 8.4 mL in 100 mL H 2 O bp 35 o C solubility 8.9 mL in 100 mL H 2 O bp 118 o C Each molecule has about the same amount of Van der Waals interactions, and the Van der Waals surfaces are relatively large. Each compound has a dipole, lone pairs on oxygen and is able to hydrogen bond with water. Therefore each compound has similar solubility in water. The hydrogen bonds in butanol are stronger that the dipole interactions in diethyl ether. Butanol has a higher boiling point because of the stronger hydrogen bonds. The intermolecular forces holding the butanol molecules together are stronger than those holding the diethyl ether molecules together. 2) Explain the difference in boiling point for the following pairs of compounds: N CH 3 H N bp 81 o C bp 106 o C and a) Each molecule has about the same Van der Waals ability. N-methyl-pyrrolidine (on the left) is capable of dipole-dipole interactions. Piperidine (on the right) has a dipole and can also hydrogen bond with itself (lone pair of electrons and hydrogen on the nitrogen atom). Therefore Piperidine has the higher boiling point. Note : The nitrogen of N-methyl-pyrrolidine has a lone pair and can hydrogen bond with water (water donates the hydrogen and is called a hydrogen bond donor). N-methyl-pyrrolidine donates the lone pair and is called a hydrogen bond acceptor. N-methyl-pyrrolidine cannot hydrogen bond with itself because there are no hydrogens on polar heteroatoms (N) in this structure. OH O bp 141 o C bp 88 o C and b) Each molecule has about the same Van der Waals ability. Both molecules have dipoles. Cyclopentanol (on the left) is capable of hydrogen bonding with itself. Tetrahydropyran (on the right) is only capable of dipole-dipole interactions. Therefore cyclopentanol has the higher boiling point since hydrogen bonds are stronger than dipole interactions.
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This note was uploaded on 10/24/2010 for the course SCIENCE 2776 taught by Professor Dr.alisonflynn during the Fall '10 term at University of Ottawa.

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assignment 2 answers - CHM 1321A Assignment #2 Answers 1)...

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