what is haloakanes & haloarenes?
Answers
Haloalkanes and Haloarenes
Nature of C-X bond in alkyl halides: X is more electronegative than carbon. So, the C-X bond is polarized with C having a partial positive charge and X having a partial negative charge.
Preparation of haloalkanes:
d) Halogen Exchange Method:
Preparation of haloarenes:
a) By elecrophilic substitution reaction:
b) Sandmeyer’s reaction:
c) Gattermann reaction:
d) From Diazonium Chloride:
e). Balz – Schiemann reaction:
Physical properties of haloalkanes:
a) Solubility
Although haloalkanes are polar in nature, yet they are practically very slightly soluble in water.
In order for a haloalkane to dissolve in water, energy is required to overcome the attractions between the haloalkane molecules and break the hydrogen bonds between water molecules.
However Haloalkanes are not able to form hydrogen bonds with water and therefore, less energy is released when new attractions are set up between the haloalkane and the water molecules because these are not as strong as the original hydrogen bonds in water molecules.
As a result, solubility of haloalkanes in water is low.
b) Density
Simple fluoro and chloroalkanes are lighter than water while bromides and polychlorodevrivatives are heavier than water.
With the increase in number of carbon atoms, the densities go on increasing. With the increase in number of halogen atoms, the densities go on increasing. The densities increase in the order: Fluoride < chloride < bromide < iodide
The density also increases with increasing number and atomic mass of the halogen.
c) Boiling Points
Molecules of organic halogen compounds are generally polar.
Due to the polarity as well as higher molecular mass as compared to the parent hydrocarbon, the intermolecular forces of attraction (dipole – dipole and van der Waals) between the molecules are stronger in halogen derivatives of alkanes.
As a result melting and boiling points of chlorides, bromides and iodides are considerably higher than those of the parent hydrocarbon of comparable molecular mass.
For the same alkyl group the boiling points of alkyl chlorides, bromides and iodides follow the order RI >RBr>RCl> RF where R is an alkyl group. This is because with the increase in the size of the halogen, the magnitude of van der Waals force increase.
In general, the boiling points of chloro, bromo and iodo compounds increase with increase in the number of halogen atoms.
For the same halogen atom, the boiling points of haloalkanes increase with increase in the size of alkyl groups.