Physical Properties of Haloalkanes and Haloarenes
Haloalkanes and haloarenes are organic compounds formed when hydrogen atoms are replaced with halogen atoms in aliphatic or aromatic hydrocarbons. Haloalkanes and haloarenes are also called alkyl halide and aryl halide respectively. Haloalkanes and haloarenes organic compounds are found in nature and some of these are very important and useful for different purposes in our day-to-day life. This compounds are used in industries, laboratories as solvent and as starting chemicals in the synthesis of organic compounds.
There are different methods from which we can prepare haloalkanes and haloarenes from chemicals. Example:
CH3-Cl ⇢ Methyl chloride
CH3-Br ⇢ Methyl Bromide
CH3CH2CH2-Br ⇢ n-Propyl bromide
CH2 = CH-Cl ⇢ Vinyl chloride
CH2 = CHCH2-Br ⇢ Allyl bromide
CHCl3 ⇢ Chloroform
Physical properties of Haloalkanes and Haloarenes
Haloalkanes and haloarenes are present in various forms and their physical properties vary with different compounds let’s discuss some important physical properties here-
- Nature and State
In their purest form, alkyl halides are colourless. When exposed to light, bromides and iodides, however, develop color. The odor of many volatile halogen compounds is sweet.
- Melting and boiling points
Methyl chloride, methyl bromide, ethyl chloride, and some chlorofluoromethanes are all gases at room temperature. Higher-level members are either liquids or solids. Organic halogen compound molecules are generally polar, as we have seen. The intermolecular forces of attraction (dipole-dipole and van der Waals) are stronger in halogen derivatives due to their higher polarity and molecular mass compared to the parent hydrocarbon. As a result, the boiling points of chlorides, bromides, and iodides are significantly higher than those of comparable molecular mass hydrocarbons.
For the same alkyl group, the boiling points of alkyl halides decrease in the following order: RI> RBr> RCl> RF. This is due to the fact that the magnitude of van der Waal forces increases with halogen atom size and mass.
The boiling points of isomer of haloalkanes decrease when the branch of hydrocarbon increases. Among the three isomers, 2-bromo-2-methylpropane has the lowest boiling point.
The boiling points of isomers of dihalobenzenes are nearly identical. The para-isomers, on the other hand, have a higher melting point than the ortho- and meta-isomers. para-isomers fit better in the crystal lattice because of their symmetry than ortho- and meta-isomers.
Hydrocarbon Bromo, iodo, and polychloro derivatives are heavier than water. The density rises as the number of carbon atoms, halogen atoms, and halogen atomic mass rise. The density of some Haloalkanes are listed below-
In water, haloalkanes are only very slightly soluble. Energy is required to overcome the attraction between the haloalkane molecules and to break the hydrogen bonds between the water molecules in order to dissolve haloalkane in water. Less energy is released because the new attractions formed between the haloalkane and the water molecules are not as strong as the original hydrogen bonds in water. As a result, haloalkanes have a low solubility in water. Haloalkanes, readily dissolve in organic solvents because the new intermolecular attractions formed by haloalkanes and solvent molecules are nearly as strong as the ones formed by the separate haloalkane and solvent molecules.
Question 1: What is haloalkane? Give examples.
Haloalkanes are halogen derivative, when hydrogen is replaced with halogen atoms in aliphatic hydrocarbon haloalkanes are produced. for example- methyl chloride (CH3-Cl), n-Propyl bromide (CH3CH2CH2-Br), Methyl Bromide (CH3-Br), n-Propyl iodide (CH3CH2CH2-I).
Question 2: What are the elements of the halogen group?
In periodic table halogens are group 17 elements which includes fluorine(F), chlorine(Cl), bromine(Br), iodine(I) and astatine(At). This elements are called halogen because they form salts when react with metals.
Question 3: How the boiling point depends for isomeric haloalkanes?
When the branch of hydrocarbon increases boiling point of isomers of haloalkane decreases. the boiling point of 2-bromo-2-methylpropane is less as compared to other isomers of it.
Question 4: In CH3CH2CH2-Cl and CH3CH2CH2-Br which one has more density and why?
The density of haloalkanes depends on mass as the mass increases density of haloalkanes increases. So CH3CH2CH2-Br has higher molecular mass than CH3CH2CH2-Cl that’s why the density order will be-
CH3CH2CH2-Br > CH3CH2CH2-Cl
Question 5: p-Dichlorobenzene has more melting point as compared to o-Dichlorobenzene and m-Dichlorobenzene why?
The para isomer of Dichlorobenzene forms a crystal lattice due to there symmetry so to melt p-Dichlorobenzene requires more energy as compared to o-Dichlorobenzene and m-Dichlorobenzene that’s why the melting point is also high.
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