CHEM 241 Lecture Notes - Lecture 1: Van Der Waals Strain, Propyl Group, Cycloalkane
20 Jan 2021
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Do not dissolve in water - hydrophobic ("water hating") Most are less dense than water ( = 0. 7 g/ml, top layer in oil-water mixes) Boiling points increase with increasing mwt (greater london forces) Boiling points decrease with increasing branching (fewer london forces) 2-methylpropane bpt -10 c butane bpt -0. 6 c. Melting points generally increase with increasing molecular weight (cf. Branched alkanes have higher mp"s than their linear counterparts because they can pack better in the crystal lattice. (cid:149) Linear alkanes with even numbers of carbons pack into the crystal lattice better than linear alkanes with odd numbers of carbon atoms and so have higher mpts. Lower homologues are oils, higher homologues are waxes. Ch2 (cid:149) can be linear or branched and are termed structural isomers. Predict the number of isomers that have the molecular formula below and indicate which isomer will have the highest bpt: c6h14, repeat for cyclo-c6h12. Initially different hydrocarbons were named according to the number of carbons.
