To determine which compound A corresponds to the organic formula C5H9Br, we need to analyze the information provided and evaluate the options based on their reactivity and structural features.
Analyzing Compound A
Given that A is C5H9Br, we identify it as a brominated compound with potential unsaturation, as indicated by its ability to decolorize bromine water and cold alkaline KMnO4. Both tests suggest the presence of a double bond (alkene) in compound A, as these reagents react with alkenes to form colorless products.
Evaluating the Options
- Option a: CH3CH2CH=C(Br)CH3
- Option b: CH3CH2-C(Br)=CHCH3
Let’s examine each of these structures:
Structure of Option A
In compound a (CH3CH2CH=C(Br)CH3), we can see that the bromine is attached to a carbon in a double bond, which can indeed participate in the decolorization of bromine water. The presence of a double bond also supports the reactivity with KMnO4.
Structure of Option B
In compound b (CH3CH2-C(Br)=CHCH3), the bromine is also directly bonded to a double-bonded carbon. Similar to compound a, this structure can also decolorize bromine water and react with KMnO4, confirming the presence of an alkene.
Further Reactions and Products
Next, we look at the reactions involving both compounds. The reaction of A with alcoholic KOH suggests an elimination reaction that could produce an alkene. The subsequent reaction with NaNH2 producing compound C with the evolution of NH3 indicates that C is possibly an amine, which aligns with the dehydrohalogenation mechanism typical of these reagents.
Hydrogenation and Isomerization
When C is treated with Lindlar’s catalyst, it is likely to undergo partial hydrogenation, resulting in compound D. The reaction with Na in liquid NH3 will lead to E, an isomer of D, suggesting that D and E have different structural configurations (likely cis/trans isomerism). This is characteristic of compounds derived from alkenes.
Conclusion on Compound A
Both options a and b meet the criteria laid out by the reactions and properties of compound A. Hence, the correct answer to your question is:
c. Both a & b
This analysis not only shows that both structures are plausible as compound A but also highlights the importance of understanding the underlying chemistry of reactions involving alkenes, brominated compounds, and the resulting products. Each step reinforces the interconnectedness of organic chemistry concepts, from structural analysis to reaction mechanisms.
