Alkanes: of propane, used in bottled gas:C3H8 + 5O2

Alkanes: Alkanes are non-polar and non-reactive hydrocarbons. Why are they non-polar? The Electronegativity difference between C and H is negligible, meaning that they share electrons equally. There is no dipole (partial charges) to attract ionic species. Why are they non-reactive? The bond energies for C-C bonds and C-H bonds are relatively high (348,412kJ/mol respectively), making the bonds very tough to break. When we combine the two factors (high bond enthalpy and being non-polar) this makes alkanes quite non-reactive. They do not react with acids/bases and oxidizing agents. But when they do react- Look out!Reactions of Alkanes:Alkanes are un-reactive except under some vigorous reactions. Combustion Oxidation Pyrolytic Cracking Halogenation Cyclo-Alkanes Reactivity1.Combustion:Fuels react with oxygen to release useful energy. Most of the energy is released in the form of heat, though light energy is also released.About 21 oxygen is present in air. When a fuel burns in excess amount of air, it receives enough oxygen for complete combustion. Complete combustion:Complete combustion needs a plenty of air so that the elements fuel react wholly with oxygen.When hydrocarbons burn completely: the carbon oxidizes to carbon dioxide the hydrogen oxidizes to water.Hydrocarbon + oxygen ? carbon dioxide + waterHere is the equation for the complete combustion of propane, used in bottled gas:C3H8 + 5O2 ? 3CO2 + 4H2O1.2. Incomplete combustion:Incomplete combustion occurs when the supply of oxygen is not sufficient. In general, for incomplete combustion: C n H 2 n+2 + O2 ? CO + C + H2OHere is the equation for the incomplete combustion of propane, where carbon is produced rather than carbon monoxide:C3H8 + 2O2 ? 3C + 4H2O2. Catalytic Oxidation:Catalytic oxidations of hydrocarbons have been explored by using various oxidizing agents, and oxidations with molecular oxygen under mild conditions are especially rewarding goals. (Conde et al., 2013)Lower Alkanes when burnt in the presence of metallic catalysts, at high temperature and pressure, results in the formation of useful products.CH_4  + O ?(???([email protected]°C )  ) CH_3 OHCH_3 OH+O ?(???(Cu @400°C) )  HCHO+H_2 OHCHO+O ?(???(Cu @400°C) ) HCOOHHCOOH+O ?(???([email protected]°C) ) CO_2+ H_2 O Catalytic Oxidation of Alkanes is used industrially to prepare higher fatty acids used in soap and vegetable oil industries. Anwar, J. et al.,(2003).3.Pyrolytic Cracking:Heat in absence of O2 ;  used in making gasoline.Alkanes?(??? )  mixture of smaller alkanes Meislich H., Nechamkin H., Jacob S., Hademenos G., (Third Edition).Alkanes, Organic Chemistry(pp-58).4.Halogenation:The halogen molecule has a nonpolar covalent bond. UV light contains sufficient energy to break the weaker nonpolar chlorine?chlorine bond (?58 kcal/mole), but it has insufficient energy to break the stronger carbon?hydrogen bond (104 kcal/mole). The fracture of the chlorine molecule leads to the formation of two highly reactive chlorine free radicals (chlorine atoms). A free radical is an atom or group that has a single unshared electron.1.Initiation: 2.Propagation:  3.Termination:(a) (b)  (c) 5.Reactivity of Cycloalkanes:Cyclic compounds show the same reactions as that of alkanes…i.e. radical substitution with chlorine and bromine. Cyclopropane is one notable exception to the generalization that cyclic and acyclic compounds undergo the same reactions. Although it is an alkane, cyclopropane undergoes electrophilic addition reaction as if it were an alkene. As the angle is 60° between three carbons arranged in a triangle in cyclopropane. sp3 orbitals cannot overlap head-on, which decreases the effectiveness of the orbital overlap.Thus, the bonds are considerably weaker than normal C-C ? bonds.Consequently, three membered ring undergoes ring-opening reactions with electrophilic reagents.SUMMARY:1. Alkanes are non-polar, non-reactive.2. Alkanes react with oxygen to form carbon dioxide and water.3. Alkanes undergo halogenations reactions.4. Alkanes crack to form certain useful compounds.5. Cyclopropane undergoes electrophilic addition reactions.


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