Bromination vs. Chlorination: Bromination is more selective (favors 3° H) but less reactive. Chlorination is less selective but more reactive, often yielding product mixtures.
Combustion: Alkanes burn completely in excess O2 to yield CO2 and H2O, releasing heat.
Wurtz Reaction: Synthesizes higher, symmetrical alkanes (R-R) from alkyl halides (RX) using Na in dry ether. Not suitable for unsymmetrical alkanes (R-R') due to product mixtures.
Must-Know Formula / Reaction
General Combustion of Alkanes: CnH2n+2 + (3n+1)/2 O2 → nCO2 + (n+1)H2O
What is the main characteristic reaction type of alkanes?▾
Alkanes are saturated hydrocarbons and primarily undergo Free Radical Substitution (FRS) reactions. This involves the homolytic cleavage of C-H bonds, typically initiated by UV light or heat.
Why is bromination considered more selective than chlorination in alkane halogenation?▾
Bromination is more selective because bromine radicals abstract hydrogen atoms more slowly, allowing them to differentiate between different types of hydrogens (3°, 2°, 1°). They preferentially abstract the hydrogen that leads to the most stable radical (tertiary) due to its lower activation energy, leading to a major product. Chlorination is faster and less discriminating.
What is the primary limitation of the Wurtz reaction in synthesizing alkanes?▾
The Wurtz reaction is excellent for synthesizing symmetrical alkanes (R-R) from a single alkyl halide. Its primary limitation arises when attempting to synthesize unsymmetrical alkanes (R-R') from two different alkyl halides (R-X and R'-X), as it leads to a mixture of three products (R-R, R'-R', and R-R') which are difficult to separate, resulting in poor yields of the desired unsymmetrical product.
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