Alkyl Halides Properties and Boiling Points

• Pure Alkyl Halides

  • Colorless in pure form

  • Bromides and iodides develop color when exposed to light

  • Many volatile halogen compounds have a sweet smell

• Physical State at Room Temperature

  • Methyl chloride, methyl bromide, ethyl chloride, and some chlorofluoromethanes are gases

  • Higher members are liquids or solids

• Molecular Polarity and Intermolecular Forces

  • Organic halogen compounds are generally polar

  • Stronger intermolecular forces due to greater polarity and higher molecular mass compared to hydrocarbons

  • Boiling points of halogen derivatives (chlorides, bromides, iodides) are higher than hydrocarbons of similar molecular mass

• Effect of Halogen Size on Boiling Points

  • Boiling points decrease in order: RI > RBr > RCl > RF

  • Increase in size and mass of halogen atom leads to stronger van der Waals forces

  • Attractions strengthen with larger molecules and more electrons

Boiling Points of Isomeric Haloalkanes and Branching

• Introduction

  • Explanation of isomeric haloalkanes

  • Relationship between boiling point and branching in haloalkanes

• Boiling Points of Isomeric Haloalkanes

  • Definition of boiling point

  • Influence of molecular structure on boiling point

• Effect of Branching on Boiling Points

  • Explanation of branching in organic compounds

  • Impact of branching on intermolecular forces

• Comparison of Isomeric Haloalkanes

  • Comparison of 1-bromo-2-methylpropane, 2-bromo-2-methylpropane, and 2-bromopropane

  • Explanation of the lowest boiling point in 2-bromo-2-methylpropane

• Conclusion

  • Recap of the relationship between branching and boiling points in isomeric haloalkanes

  • Importance of understanding structure-property relationships in organic compounds

Boiling Points and Melting Points of Isomeric Dihalobenzenes

• Boiling Points of Isomeric Dihalobenzenes

  • Boiling points of isomeric dihalobenzenes are very similar.

  • Para-isomers have higher melting points compared to ortho and meta-isomers.

• Reason for Higher Melting Points of Para-Isomers

  • Symmetry of para-isomers allows them to fit better in crystal lattice.

  • Better fit in crystal lattice leads to higher melting points.

• Density of Halogen Derivatives

  • Bromo, iodo, and polychloro derivatives of hydrocarbons are denser than water.

• Factors Affecting Density

  • Density increases with:

    • Increase in the number of carbon atoms.

    • Increase in the number of halogen atoms.

    • Increase in the atomic mass of the halogen atom.

Solubility of Haloalkanes

• Solubility in Water

  • Very slightly soluble in water

  • Energy required to dissolve haloalkane in water

  • Overcoming attractions between haloalkane molecules and breaking hydrogen bonds in water

  • New attractions between haloalkane and water molecules are weaker than original hydrogen bonds in water

  • Low solubility in water due to weaker attractions

• Solubility in Organic Solvents

  • Haloalkanes tend to dissolve in organic solvents

  • New intermolecular attractions between haloalkanes and solvent molecules

  • Strength of attractions between haloalkanes and solvent molecules similar to those being broken in separate molecules