2.1 Handout (Predicting BPs and MPs)

2.1 Handout (Predicting BPs and MPs) - Predicting boiling...

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Predicting boiling point, melting point, and solubility trends. Introduction: Many of the properties of organic molecules can be predicted based on the strength of their cohesive molecule-molecule interactions (ie how much the molecules want to stick together). The boiling point (BP) and melting point (MP) of an organic molecule is related to: 1) the molecular weight of the molecule and 2) the "stickiness" of individual molecules for their neighbors. For example, molecules in a liquid are held together by attractive interactions between molecules. These interactions must be broken (by adding heat) in order to transition into the gas. The stronger the cohesive interactions, the more heat that is necessary for the liquid-to-gas phase transition. K. Shimizu In order to undergo a phase change, energy (in the form of heat) is required to break the cohesive molecule- molecule interactions. interaction nature of attraction strength types of functional groups dipole-dipole strong molecular dipoles generate partial charges ( δ + and δ -) weak ketones, esters, (C=O), alkyl halides , (any molecule with a dipole or a strongly polarized bond) liquid gas stronger cohesive forces (more sticky) higher boiling point higher melting point and greater solubility in water* heat Therefore: All of the attractive intermolecular forces are based on the electrostatic attraction of
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This note was uploaded on 02/03/2012 for the course CHEM 333 taught by Professor Lavigne during the Spring '09 term at South Carolina.

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2.1 Handout (Predicting BPs and MPs) - Predicting boiling...

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