a) CH3-CH2-CH3 (g) + Br2 (l) -->
This is called a substitution reaction in organic chemistry because the hydrogens in the alkane get replaced or substituted with halogen atoms, one at a time. If we start with replacing just one hydrogen, there are two possible products, 1-bromopropane and 2-bromopropane, with 2-bromopropane being the major product:
Br
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CH3CH2CH3 + Br2 ––�?gt; CH3CHCH3 + HBr
This kind of selectivity of the product is called regioselectivity in organic chemistry. The bromine bonds preferentially at one atom or "region" in the propane molecule. It turns out that the lowest energy reaction pathway (the reaction mechanism) leads to 2-bromopropane in this reaction.
b) C7H16 (l) + O2 (g) -->
Complete combustion of any organic compound containing the elements C, H, and/or O gives only the products CO2 and H2O. First balance the carbons, then the hydrogens, and lastly the oxygens by putting the necessary coefficient in front of O2.
c) CH3-CH2-CH2-CH3 (g) + CH3-CH3 (g) -->
There shouldn't be any reaction between two alkanes. In fact alkanes are generally unreactive. Their major reactions are halogenation (reaction 'a' above) and combustion. There are alkane "cracking" reactions that can occur between alkane radicals, but as written this does not look like one of those.
d) H H H
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H–C––C––C–H + F2 (g) -->
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H H H
This is just like reaction (a). The hydrogen atoms will get replaced by fluorine atoms in this case. A big difference with fluorination, compared to chlorination and bromination, is that reactions of alkanes with F2 are highly exothermic, even explosive, and as a result are difficult to control. We can give the monofluorinated major product 2-fluoropropane as we did in reaction (a). Assuming the C–C bonds survive, all of the hydrogens can be replaced with fluorine atoms, giving 1,1,1,2,2,3,3,3-octafluoropropane, or "perfluroropropane" :
H H H F F F
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H–C––C––C–H + 8 F2 (g) ––�?gt; F–C––C––C–F + 8 HF
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H H H F F F
The product you choose for fluorinations may depend on how your particular textbook and/or teacher presents them!
Steve
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