Hopanes are found in petroleum and geologic sediments

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: e found in petroleum and geologic sediments. 2.20 2.20 Physical Properties of Alkanes and Cycloalkanes Boiling Point Boiling Boiling points of n-alkanes increase with increasing molecular weight (number of carbons). Branched alkanes generally have lower boiling points than unbranched alkanes with the same number of carbons. Intermolecular Forces and Boiling Point Intermolecular Attractive forces between molecules in the liquid phase affect the boiling point of the liquid. These Intermolecular forces are van der Waals forces and may be divided into three types: Dipole-dipole (including hydrogen bonding); Induced dipole-dipole; or Induced dipole-induced dipole. Intermolecular Forces and Alkanes Intermolecular Alkanes have no dipole so the van der Waals forces are the temporary induced dipole-induced dipole. This interaction is dynamic and fluctuates. Intermolecular Forces and Alkanes Intermolecular Long chain alkanes have more induced dipole-induced dipole interactions so the boiling point increases with increasing chain length. Intermolecular Forces and Alkanes Intermolecular Branched alkanes have lower surface area than isomeric nalkanes and therefore have lower boiling points. Melting Point Melting Solid n-alkanes are soft low melting solids. The same intermolecular forces hold the molecules together in the solid state. Solubility of Alkanes in Water Solubility Alkanes (and all hydrocarbons) are virtually insoluble in water and are said to be hydrophobic. The densities of most alkanes are in the range 0.6-0.8 g/mL therefore alkanes float on the surface of water. 2.22 2.22 Physical Properties of Alkanes and Cycloalkanes Acidity of Hydrocarbons Acidity Hydrocarbons are very weak acids. Alkynes have the Hydro...
View Full Document

Ask a homework question - tutors are online