Chemistry Chapter 9: Amines and Reactions

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Questions and Answers

What is the outcome when benzene is converted into aniline?

Formation of an ether

Replacement of a hydrogen atom with an amino group (correct)

Formation of a ketone

Addition of chlorine

Why are lower aliphatic amines soluble in water?

They have a higher molecular weight

They have stronger intermolecular forces than alcohols

They are more polar than alcohols

They can form hydrogen bonds with water molecules (correct)

Which amine is likely to exhibit higher solubility in water?

Butan-1-ol

Hexan-1-amine

Butan-1-amine (correct)

Pentane

What distinguishes primary amines in terms of boiling points compared to secondary amines?

Primary amines engage in more intermolecular hydrogen bonding Signup and view all the answers

What happens to the solubility of amines in water as their molecular mass increases?

Solubility decreases Signup and view all the answers

Which type of amine is represented by the formula R-NH₂?

Primary amine Signup and view all the answers

What is the boiling point of n-C₄H₉NH₂?

350.8 K Signup and view all the answers

What reaction occurs when an amine reacts with an acid?

Formation of a salt Signup and view all the answers

What property allows amines to behave as nucleophiles?

Presence of unshared electron pairs Signup and view all the answers

Which compound would likely have the highest boiling point among the given amines?

n-C₄H₉OH Signup and view all the answers

What happens when amine salts are treated with a base like NaOH?

They regenerate the parent amine. Signup and view all the answers

Which of the following statements correctly describes the nature of amines?

Amines contain an unshared pair of electrons on nitrogen. Signup and view all the answers

Which of the following amines is the strongest base based on its pKa value?

N,N-Dimethylmethanamine Signup and view all the answers

Why are aliphatic amines generally stronger bases than ammonia?

They possess the +I effect of alkyl groups. Signup and view all the answers

What is the pKa value range for aliphatic amines compared to ammonia?

3.00 to 4.22 Signup and view all the answers

What factor most significantly affects the basicity of amines?

The ease of formation of the cation from the amine Signup and view all the answers

In the gaseous phase, which amine has the highest basicity according to the order presented?

Tertiary amine (3° amine) Signup and view all the answers

Why are alkanamines considered stronger bases than ammonia?

Alkanamines have electron-donating alkyl groups that stabilize the cation Signup and view all the answers

When considering basicity in an aqueous state, what factor decreases the stability of substituted ammonium ions?

The size of the alkyl group Signup and view all the answers

What is the expected trend in stability of substituted ammonium cations as the number of alkyl groups increases?

Stability increases with more alkyl groups Signup and view all the answers

What is the order of decreasing basic strength among the following compounds?

(CH3)2NH > CH3CH2NH2 > NH3 > CH3NH2 Signup and view all the answers

What type of reaction occurs when amines react with acid chlorides or anhydrides?

Acylation Signup and view all the answers

What is produced when amines react with carboxylic acids at room temperature?

Salts Signup and view all the answers

What is the role of pyridine in the acylation reaction of amines?

To remove HCl produced Signup and view all the answers

Which of the following is the product of the reaction of methanamine with benzoyl chloride?

N-Methylbenzamide Signup and view all the answers

What is the correct order of basicity for aliphatic amines?

primary > secondary > tertiary Signup and view all the answers

Which factor causes a decrease in basic strength when altering the alkyl group from -CH3 to -C2H5?

Increase in steric hindrance Signup and view all the answers

Why does aniline have a high pKa value compared to ammonia?

Because the nitrogen's lone pair is in resonance with the benzene ring Signup and view all the answers

Which of the following groups would increase the basic strength of substituted aniline?

-OCH3 Signup and view all the answers

How many resonating structures exist for aniline?

Five Signup and view all the answers

Which amine is the strongest base in aqueous solution?

(C2H5)3NH Signup and view all the answers

What effect does an electron-withdrawing group have on the basic strength of aniline?

It decreases the basic strength Signup and view all the answers

How many resonating structures are there for the anilinium ion?

Two Signup and view all the answers

Study Notes

Conversion Reactions

Benzene can be converted into aniline through the nitration of benzene followed by reduction.
The synthesis of N,N-dimethylaniline from benzene involves alkylation with dimethyl sulfate or methyl iodide.
Cl(CH₂)₄Cl can be transformed into hexan-1,6-diamine via a nucleophilic substitution reaction with ammonia.

Physical Properties of Amines

Lower aliphatic amines are gases with a fishy odor; primary amines with three or more carbons are liquids; higher aliphatic amines are solids.
Aryl amines, like aniline, are usually colorless but develop color upon prolonged storage due to oxidation.
Lower aliphatic amines are water-soluble due to hydrogen bonding; solubility decreases with increased molar mass due to hydrophobic alkyl groups.
Amines are soluble in organic solvents but, unlike alcohols, are less polar and form weaker hydrogen bonds.

Behavior and Basicity of Amines

Amines react with acids to form salts due to their basic character (e.g., R-NH₂ + HX → R-NH₃⁺X⁻).
Basic strength is assessed via pKa values, with strong bases having lower pKa values.
Aliphatic amines typically have pKa values between 3 to 4, while aromatic amines like benzenamine have a significantly higher pKa of 9.38, indicating weaker basicity due to resonance effects.

Boiling Points of Amines, Alcohols, and Alkanes

Boiling points increase with increased molar mass but vary based on molecular structure and hydrogen bonding capacity.
Primary amines show the highest boiling points due to stronger intermolecular hydrogen bonding compared to secondary and tertiary amines.

Structure and Basicity Relationship

Basicity is influenced by the stability of the protonated amine cation formed during protonation.
Alkyl groups enhance basicity through +I effect, making electron pairs more available.
The general order of basicity for aliphatic amines is primary > secondary > tertiary, contrary to expectations from inductive effects due to steric hindrance.

Acid-Base Behavior

Primary amines undergo intermolecular hydrogen bonding, enhancing their basic character.
Tertiary amines lack hydrogen for bonding, thus showing weaker intermolecular interactions and basicity compared to primary amines.

Arylamines Basicity

Aryl amines have lower basicity than aliphatic amines due to resonance stabilization of the lone pair on nitrogen adjacent to the aromatic ring.
Substituents on the aryl ring influence the basicity: electron-donating groups increase basicity, while electron-withdrawing groups decrease it.

Reactions of Amines

Alkylation involves amines reacting with alkyl halides, while acylation deals with amines reacting with acid chlorides or anhydrides to form amides.
The reaction of amines with carboxylic acids produces ammonium salts, illustrating their basic behavior.

Summary of Basicity Order

The order of decreasing basic strength among various amines such as CH₃NH₂, CH₃CH₂NH₂, (CH₃)₂NH, NH₃ is: (CH₃)₂NH > CH₃CH₂NH₂ > NH₃ > CH₃NH₂.

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Description

Explore the transformation of benzene into various amines including aniline and N,N-dimethylaniline. This quiz also covers the physical properties of lower aliphatic amines and their solubility characteristics. Test your understanding of amine reactions and properties!