what alkane could you use to prepare 1,2 dichloro-3- methylpentane? Write the balance chemical equation, showing the alkane and the other required reagent
The correct answer and explanation is:
To prepare 1,2-dichloro-3-methylpentane, the appropriate starting alkane is:
3-methylpentane
Balanced Chemical Equation:
C6H14+2Cl2→UV lightC6H12Cl2+2HCl\text{C}_6\text{H}_{14} + 2\text{Cl}_2 \xrightarrow{\text{UV light}} \text{C}_6\text{H}_{12}\text{Cl}_2 + 2\text{HCl}
Where:
- C₆H₁₄ = 3-methylpentane (the alkane)
- Cl₂ = chlorine (halogen used for substitution)
- C₆H₁₂Cl₂ = 1,2-dichloro-3-methylpentane (the target compound)
- HCl = byproduct of the substitution reaction
Explanation (Approximately 300 words):
To synthesize 1,2-dichloro-3-methylpentane, you must begin with the correct alkane skeleton. The target compound has six carbon atoms total and a methyl group attached to the third carbon of the main chain, which indicates 3-methylpentane is the correct parent hydrocarbon.
3-methylpentane has the molecular formula C₆H₁₄ and consists of a straight chain of five carbon atoms with a methyl group on the third carbon. In the desired product, chlorine atoms are substituted at the 1st and 2nd carbon positions of this structure.
This type of reaction is a free radical halogenation, where halogen atoms (in this case, chlorine) replace hydrogen atoms on the alkane in the presence of UV light. This reaction proceeds via a radical chain mechanism: initiation, propagation, and termination.
In this case, two chlorine molecules (Cl₂) are required because two hydrogen atoms (on carbon 1 and carbon 2) are replaced by chlorine atoms. The byproducts are two molecules of hydrogen chloride (HCl).
However, a challenge with free radical halogenation is its lack of selectivity. Chlorination tends to give a mixture of products, including mono-, di-, and poly-chlorinated compounds at various positions. Therefore, to favor 1,2-dichloro-3-methylpentane, reaction control or purification (e.g., distillation or chromatography) would be necessary to isolate the desired compound.
In summary, 3-methylpentane reacts with Cl₂ in the presence of UV light to form 1,2-dichloro-3-methylpentane via substitution of hydrogen atoms on adjacent carbon atoms. The process also yields HCl as a byproduct.