Ch_322a_2.012

Ch_322a_2.012 - Influence of Molecular Shape In addition to...

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Influence of Molecular Shape In addition to polar influences, the melting point of organic compounds is affected by molecular shape . Molecules that are more symmetrical tend to pack better in the solid state, and have higher melting points than comparable molecules with other shapes. Alcohol Isomers of C 4 H 10 O CH 3 -C-OH CH 3 CH 3 CH 3 CH 2 CH 2 CH 2 OH CH 3 CHCH 2 OH CH 3 CH 3 CH 2 CHOH CH 3 tert-butyl alcohol butyl alcohol isobutyl alcohol sec.-butyl alcohol MP 25 o C -90 o C -108 o C -114 o C
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Additional Examples Alkanes and Cycloalkanes CH 3 CH 2 CH 3 CH 3 CH 2 CH 2 CH 3 MP -188 o C -127 o C -138 o C -50 o C BP -42 o C -32 o C -0.5 o C 12.5 o C The more compact cycloalkanes have melting points significantly higher than the comparable alkanes. The boiling points for these small sized alkanes and cycloalkanes are not very different.
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Van Der Waals Forces There are examples where the boiling point of a more spherical alkane is lower than comparable elongated isomer structures. An example is neopentane (bp 9.4
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_2.012 - Influence of Molecular Shape In addition to...

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