Chapter 15, Problem 1MCP

(a)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ has a lower melting point than $\text{1-}$ octanol” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is true.

Explanation of Solution

$\text{N-ethyl-1-hexanamine}$ is an amine and $\text{1-}$ octanol is an alcohol.

Alcohols have strong intermolecular hydrogen bonding.  The $\text{OH}$ group present in the alcohol allows the molecules to participate in hydrogen bonding.  A larger amount of energy is required to break the intermolecular hydrogen bonding in alcohols hence, they have higher boiling and higher melting points compared to amines of comparable molar mass.

On the other hand, the polarity of the amine nitrogen is less than the oxygen in alcohol.  The nitrogen amine is less electronegative than oxygen in the alcohol.  Therefore, the dipole on $\text{N-H}$ is much weaker than the dipole on $\text{O-H}\text{.}$  Hence, the melting point of $\text{N-ethyl-1-hexanamine}$ is lower than that of $\text{1-}$ octanol.

(b)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ has a higher boiling point than octanoic acid” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is false because of the presence of strong intermolecular hydrogen bonding in octanoic acid, it has higher boiling point than $\text{N-ethyl-1-hexanamine}$.

Explanation of Solution

$\text{N-ethyl-1-hexanamine}$ is an amine and octanoic acid is an carboxylic acid.

Carboxylic acids have strong intermolecular hydrogen bonding with each other and strong dipole-dipole attractions.  The presence of polar carboxyl group and intermolecular hydrogen bonding makes these acids have higher boiling points.  The presence of dimers increases the strength of the van der Waals dispersion forces, which makes them have high boiling points.

The ability of primary and secondary amines to form $\text{N-H---N}$ hydrogen bond is reflected in their boiling points.  Because the nitrogen atom is less electronegative than the oxygen atom, the $\text{N-H}$ bond is less polar than the $\text{O-H}$ bond.  Thus, amines have lower boiling points than carboxylic acids.

Hence, the statement “$\text{N-ethyl-1-hexanamine}$ has a higher boiling point than octanoic acid” is false.

(c)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is not soluble in water” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is true.

Explanation of Solution

Amine with five or fewer carbon atoms is soluble in water.

$\text{N-ethyl-1-hexanamine}$ is a secondary chain with seven carbon atoms.  The solubility decreases with the increase in the length of the carbon-chain.  Therefore, the given statement is true.

(d)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is polar” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is true.

Explanation of Solution

In $\text{N-ethyl-1-hexanamine,}$ the nitrogen atom is more electronegative than the hydrogen atoms.  The $\text{N-H}$ bond is polar.  Hence, the given statement is true.

(e)

Interpretation Introduction

Interpretation:

The line formula of $\text{N-ethyl-1-hexanamine}$ has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given line formula of $\text{N-ethyl-1-hexanamine}$ is true.

Explanation of Solution

The given line formula is,

The above line formula represents $\text{N-ethyl-1-hexanamine}\text{.}$  Hence, the given statement is true.

(f)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is a solid at room temperature” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is false because $\text{N-ethyl-1-hexanamine}$ is a liquid at room temperature.

Explanation of Solution

$\text{N-ethyl-1-hexanamine}$ is a liquid at room temperature.  Hence the given statement is false.

(g)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is tertiary amine” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is false because it secondary amine.

Explanation of Solution

The structure of $\text{N-ethyl-1-hexanamine}$ is,

From the structure of $\text{N-ethyl-1-hexanamine}$, it is noticed that two alkyl groups namely ethyl and hexyl are bonded to nitrogen containing one hydrogen atom, hence it is secondary amine.  Therefore, the given statement is false because $\text{N-ethyl-1-hexanamine}$ is a secondary amine.

(h)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is produced by the reduction of $\text{N-ethylhexanamide}$” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is true.

Explanation of Solution

Reduction of amides in the presence of ${\text{LiAlH}}_{\text{4}}$ gives amines.  $\text{N-ethyl-1-hexanamine}$ is obtained from the reduction of $\text{N-ethylhexanamide}$.  The reaction is,

(i)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is isomer of $\text{N-ethylhexanamide}$” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is false because they have different structural and molecular formulas.

Explanation of Solution

The structure of $\text{N-ethylhexanamide}\left({\text{C}}_{\text{8}}{\text{H}}_{\text{17}}\text{NO}\right)$ is,

The structure of ${\text{N-ethyl-1-hexanamine (C}}_{\text{8}}{\text{H}}_{\text{19}}\text{N)}$ is,

$\text{N-ethyl-1-hexanamine}$ and $\text{N-ethylhexanamide}$ are not isomers to each other since they have different structural and molecular formulas.

(j)

Interpretation Introduction

Interpretation:

The statement “The reaction of $\text{N-ethyl-1-hexanamine}$ with strong base is a neutralization reaction” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is false because the neutralization reaction of the $\text{N-ethyl-1-hexanamine}$ is done in the presence of strong acid.

Explanation of Solution

$\text{N-ethyl-1-hexanamine}$ is neutralized in the presence of strong acid such as hydrogen bromide to give salt of ethylhexylammonium bromide.  The reaction is,

Hence the given statement is false because the neutralization reaction of $\text{N-ethyl-1-hexanamine}$ is done in the presence of strong acid.

(k)

Interpretation Introduction

Interpretation:

The statement “The alkyl ammonium salt would be more water soluble than the amine” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is true.

Explanation of Solution

By adding a strong acid to a water-insoluble amine, a water-soluble alkylammonium salt can be formed.  The salt could be converted back to an amine by reaction with strong base.

Alkyl ammonium salts can neutralize hydroxide ions.  Water is formed and the protonated amine cation is converted into an amine.  The nitrogen atom of an ammonium salt has a positive charge, alkyl ammonium salts are more water-soluble than amines.

(l)

Interpretation Introduction

Interpretation:

The statement “$\text{N-ethyl-1-hexanamine}$ is a heterocyclic amine” has to be predicted as true or false.  If the statement is false, the reason for the false statement has to be described.

Answer to Problem 1MCP

The given statement is false because it is not a cyclic compound.

Explanation of Solution

The structure of ${\text{N-ethyl-1-hexanamine (C}}_{\text{8}}{\text{H}}_{\text{19}}\text{N)}$ is,

$\text{N-ethyl-1-hexanamine}$ does not show any cyclic structure or does not show the presence of nitrogen atom in ring.  Therefore, the given statement is false.