Properties, Reactions and Some Important Compounds.
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Transcript of Properties, Reactions and Some Important Compounds.
Physical Properties of AlkanesBoiling pointThe boiling points of alkanes are generally
lower than those of the other compounds with comparable molecular weights
As the number of carbon atoms increases, boiling point also increases
The boiling point of constitutional isomers of alkanes decreases as branching increases (Ex. Hexane = 68.7, 3-methylpentane = 63.3, 2,3 dimethylbutane = 58.0)
Physical Properties of AlkanesInsoluble in water but soluble in organic
solvents such as toluene and diethyl ether
Because of the nonpolar nature of alkanes, they are not soluble in (polar) water.
Physical Properties of AlkanesAll liquid and solid alkanes are less dense
than water; they float on water
Exercise:Arrange the following alkanes in order of
decreasing boiling points:1.butane, decane and hexane2.2-methylheptane, octane, 2,2,4-
trimethylpentane3.2-methylbutane, pentane 2,2
dimethylpropane4.3,3-dimethylheptane, nonane, 2,2,4-
trimethylhexane
Answer1. decane, hexane, butane2. Octane, 2-methylheptane, 2,2,4-
trimethylpentane3. Pentane, 2-methylbutane, 2,2-
dimethylpropane4. Nonane, 3,3-dimethylheptane, 2,2,4-
trimethylhexane
Reactions of AlkanesHalogenation (Reaction with Halogens) –
substitution reaction
CH4 + Cl2 ------ CH3Cl + HCl
CH3Cl + Cl2 ----- CH2Cl2 + HCl
CH2Cl2 + Cl2 ----- CHCl3 ---- CCl4
Important AlkanesMethane – natural gasPropane - component of LPGButane – fuel in lighterOctane – aviation fuelHigh MW alkanes are found in waxes of
several plants. Example, the wax found in apple skin (C27H56), paraffin wax is used in making candles.
Important AlkanesHaloalkanes1. Chloroflurocarbons (CFC) – nontoxic,
nonflammable, odorless and noncorrosive. Industrial name is freon . Commonly used CFCs are trichlorofluromethane (CCl3F, Freon 11) and dichlorodifluoromethane (CCl2F2, Freon 12). Used as industrial cleaning solvents to prepare surfaces for coatings, to remove cutting oils and waxes from millings and to remove protective coatings. They are also used as propellants for aerosol sprays
Important Alkanes2. Solvents – several low MW haloalkanes
are excellent solvents; used as cleaners and degreasers. Most commonly used are CCl4 (discontinued because it was found to be toxic and carcinogenic), CHCl3 and CH2Cl2.