e-Consult | Revision Qns

1.

Describe the reaction of 1-bromopropane with magnesium to form a reagent. Write the balanced chemical equation for the reaction. Explain the role of the reagent formed in a subsequent reaction with an unreacted 1-bromopropane. State the name of the reagent and the subsequent reaction.

Reaction with Magnesium:

1-Bromopropane reacts with magnesium metal to form propene magnesium bromide (also known as isopropylmagnesium bromide), a Grignard reagent. The balanced chemical equation is:

C₃H₇Br + Mg -> C₃H₇MgBr

Role of the Grignard Reagent:

The Grignard reagent is a strong nucleophile and a strong base. It reacts with unreacted 1-bromopropane in a reaction called a Wurtz coupling. The Grignard reagent attacks the carbon-carbon bond of the 1-bromopropane, forming a new carbon-carbon bond and producing a dimer, 1,1,2-tripentamethylbutane.

Name of Reagent and Reaction:

Reagent: Propene magnesium bromide (Isopropylmagnesium bromide)

Reaction: Wurtz Coupling

2.

Question 1

The molecular formula of a compound is C₄H₁₀O. State the possible functional groups present in this compound and draw structural formulae for at least two different organic compounds that have this molecular formula. Explain, using structural formulae, how these compounds differ in terms of their chemical properties.

Possible Functional Groups: The molecular formula C₄H₁₀O suggests the presence of an alcohol (-OH) or an ether (-O-) functional group. It's possible to have both present in a single molecule.

Structural Formulae:

Butan-1-ol: CH₃CH₂CH₂CH₂OH

Butan-2-ol: CH₃CH₂CH(OH)CH₃

Diethyl ether: CH₃CH₂OCH₂CH₃

Methyl propyl ether: CH₃OCH₂CH₂CH₃

Differences in Chemical Properties:

Butan-1-ol (Alcohol): Contains a hydroxyl (-OH) group. This makes it polar and capable of hydrogen bonding. It can undergo reactions such as oxidation (to aldehydes or carboxylic acids), esterification (with carboxylic acids), and dehydration (to alkenes). It is generally more reactive than ethers.

Butan-2-ol (Alcohol): Similar to butan-1-ol, but the hydroxyl group is attached to a secondary carbon. This affects its reactivity. It can undergo oxidation, but the oxidation products are different. The secondary carbon also allows for reactions like elimination (dehydration) to form alkenes.

Diethyl ether (Ether): Contains an ether linkage (-O-). It is relatively non-polar and does not readily hydrogen bond. It is generally unreactive under normal conditions, but can be cleaved under strongly acidic conditions. It is often used as a solvent.

Methyl propyl ether (Ether): Similar to diethyl ether, but with a different alkyl group attached to the oxygen. Its properties are similar to diethyl ether.

3.

The combustion of alkanes is a useful source of energy. Describe the reaction of methane (CH₄) with excess oxygen in the presence of UV radiation. Include in your answer the balanced chemical equation, the conditions required for the reaction to occur, and the products formed. Explain why UV radiation is necessary.

The combustion of methane (CH₄) with excess oxygen is a highly exothermic reaction. The balanced chemical equation is:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

This reaction requires the presence of a catalyst, typically UV radiation. The reaction proceeds via a free radical chain mechanism. UV radiation provides the energy to break bonds in oxygen molecules, generating highly reactive oxygen radicals. These radicals then initiate a chain reaction, abstracting hydrogen atoms from methane molecules and forming alkyl radicals. These alkyl radicals then react with oxygen radicals to form products.

The conditions required for the reaction to occur are:

Excess oxygen: Ensures complete combustion.

UV radiation: Provides the activation energy to initiate the free radical chain reaction.

Methane: The reactant being combusted.

The products formed are carbon dioxide (CO₂) and water (H₂O), both in gaseous form. The reaction is highly exothermic, releasing a significant amount of energy.

Organic chemistry (3)

Question 1