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Name and outline a mechanism for step 1. Give the IUPAC name of the product of step 2. Draw the structure of the species present in the solid amino acid.

Chemistry

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Part a· 2 steps

Name and outline a mechanism for step 1

Step 1 involves the reaction of propanal (CH3_3CH2_2CHO) with hydrogen cyanide (HCN) to form 2-hydroxybutanenitrile (CH3_3CH2_2CH(OH)CN). This is a nucleophilic addition reaction.

Name of mechanism: Nucleophilic addition

Mechanism:

  1. The cyanide ion (CN−^-), a nucleophile, attacks the electrophilic carbon of the carbonyl group.

    The π\pi bond breaks, and electrons move to the oxygen atom, forming an alkoxide intermediate.

    CH3CH2CHO+CN−⟶CH3CH2CH(O−)CN\text{CH}_3\text{CH}_2\text{CHO} + \text{CN}^- \longrightarrow \text{CH}_3\text{CH}_2\text{CH}(\text{O}^-)\text{CN}

  2. The alkoxide intermediate is protonated by HCN (or H+^+ from the solution) to form the cyanohydrin.

    CH3CH2CH(O−)CN+HCN⟶CH3CH2CH(OH)CN+CN−\text{CH}_3\text{CH}_2\text{CH}(\text{O}^-)\text{CN} + \text{HCN} \longrightarrow \text{CH}_3\text{CH}_2\text{CH}(\text{OH})\text{CN} + \text{CN}^-

Part b

Give the IUPAC name of the product of step 2.

The product of step 2 is CH3_3CH2_2CH(OH)CN. This is 2-hydroxybutanenitrile.

IUPAC name: 2-hydroxybutanenitrile

Part c· 4 steps

For step 3, give the reagent, give a necessary condition and name the mechanism.

Step 3 involves the conversion of 2-hydroxybutanenitrile (CH3_3CH2_2CH(OH)CN) to 2-aminobutanoic acid (CH3_3CH2_2CH(NH2_2)COOH), which is amino acid X. This is a two-step process: hydrolysis of the nitrile to a carboxylic acid and reduction of the hydroxyl group to an amino group. However, the diagram shows the conversion of the nitrile to an amine, then to a carboxylic acid. Let's re-evaluate based on the provided diagram.

The diagram shows:

  1. CH3_3CH2_2CHO →HCN\xrightarrow{\text{HCN}} CH3_3CH2_2CH(OH)CN

  2. CH3_3CH2_2CH(OH)CN →HBr\xrightarrow{\text{HBr}} CH3_3CH2_2CH(Br)CN

  3. CH3_3CH2_2CH(Br)CN →NH3\xrightarrow{\text{NH}_3} CH3_3CH2_2CH(NH2_2)CN

  4. CH3_3CH2_2CH(NH2_2)CN →H2O/H+\xrightarrow{\text{H}_2\text{O/H}^+} CH3_3CH2_2CH(NH2_2)COOH (Amino acid X)

    For step 3:
    Reagent: NH3_3 (ammonia)
    Conditions: Reflux
    Name of mechanism: Nucleophilic substitution (specifically, SN_N2, where ammonia acts as a nucleophile replacing the bromine atom).

Part d(i)

Draw the structure of the species present in the solid amino acid.

At room temperature, the amino acid X exist as a solid (Zwitterion).

Amino acid X is 2-aminobutanoic acid. In its zwitterionic form, the amino group is protonated (-NH3+_3^+) and the carboxylic acid group is deprotonated (-COO−^-).

A Zwitterion form:

CH3CH2CH(NH3+)COO−\text{CH}_3\text{CH}_2\text{CH}(\text{NH}_3^+)\text{COO}^-

Part d(ii)

With reference to your answer to part (d) (i), explain why the melting point of the amino acid X is higher than the melting point of CH3_3CH2_2CH(OH)COOH.

Amino acid X (2-aminobutanoic acid) exists as a zwitterion, which is an ionic species. The zwitterions are held together by strong electrostatic forces of attraction between the positively charged ammonium group and the negatively charged carboxylate group. These strong ionic bonds require a significant amount of energy to overcome, leading to a high melting point.

In contrast, CH3_3CH2_2CH(OH)COOH (2-hydroxybutanoic acid) is a neutral molecule. While it can form hydrogen bonds due to the -OH and -COOH groups, these intermolecular forces are much weaker than the ionic bonds present in the zwitterionic form of the amino acid. Therefore, less energy is required to overcome these forces, resulting in a lower melting point.

Reasons:

  1. Amino acid X exists as a zwitterion, which is an ionic compound.
  2. Zwitterions form strong electrostatic forces of attraction (ionic bonds) between the positive and negative charges, requiring more energy to break compared to the weaker intermolecular forces (like hydrogen bonds) in 2-hydroxybutanoic acid.
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