Problem 33 - Chemistry and Chemical Reactivity

Question

Write the formula and draw the structure for each of the following amines: (a) ethylamine (b) dipropylamine (c) butyldimethylamine (d) triethylamine

Step-by-Step Solution

Answer

(a) C2H5NH2; H2N-CH2-CH3 (b) C6H15N; CH3-CH2-CH2-NH-CH2-CH2-CH3 (c) C6H15N; CH3-N(CH3)-CH2-CH2-CH2-CH3 (d) C6H15N; (CH2-CH3)3N

Step 1: Understanding Amines

Amines are organic compounds characterized by the presence of a nitrogen atom bonded to hydrogen atoms and/or alkyl or aryl groups. Their general formula can be expressed as R-NH2, R2-NH, or R3-N, depending on how many organic groups (R) are attached to the nitrogen.

Step 2: Determine the Formula for Ethylamine

Ethylamine consists of an ethyl group (C2H5) attached to an amino group (NH2). The molecular formula can be written as C2H5NH2.

Step 3: Draw the Structure for Ethylamine

Draw a nitrogen atom bonded to two hydrogen atoms (NH2) and then connect it to a two-carbon chain (C2H5), which means the nitrogen is attached to a CH2-CH3 chain. The structure looks like this: H2N-CH2-CH3.

Step 4: Determine the Formula for Dipropylamine

Dipropylamine consists of two propyl groups each attached to the nitrogen. The molecular formula is C3H7-NH-C3H7 or (C6H15N when combined).

Step 5: Draw the Structure for Dipropylamine

Draw the nitrogen atom, add one hydrogen atom and connect it to two propyl groups (each C3H7): CH3-CH2-CH2-NH-CH2-CH2-CH3.

Step 6: Determine the Formula for Butyldimethylamine

Butyldimethylamine includes a butyl group (C4H9) and two methyl groups (CH3) connected to the nitrogen. Its formula is C4H9-N(CH3)2.

Step 7: Draw the Structure for Butyldimethylamine

Position the nitrogen atom in the center, attach two methyl groups (CH3) and one butyl group (C4H9): CH3-N(CH3)-CH2-CH2-CH2-CH3.

Step 8: Determine the Formula for Triethylamine

Triethylamine has three ethyl groups attached to the nitrogen atom. The molecular formula is (C2H5)3N or C6H15N.

Step 9: Draw the Structure for Triethylamine

Connect the nitrogen atom to three ethyl groups (each C2H5): (C2H5)3N, or depicted as: CH3-CH2-N(CH2-CH3)-CH2-CH3.

Key Concepts

Ethylamine

Ethylamine is a simple primary amine that consists of an ethyl group (C2H5) attached directly to an amino group (NH2). This structure allows ethylamine to be expressed with the molecular formula C2H5NH2.
In simpler terms, the ethyl group is the homogenous two-carbon chain which joins with the nitrogen atom of the amino group.

• The formula: C2H5NH2.
• The structure: H2N-CH2-CH3.

Ethylamine often acts as a building block in chemical synthesis due to its simple yet reactive nature. It is also commonly encountered in its gaseous state or as a colorless liquid at room temperature.
This amine generally has a distinct fishy or ammonia-like odor due to the volatile nitrogen compounds.

Dipropylamine

Dipropylamine is categorized as a secondary amine. Its distinct trait is two propyl groups (C3H7) bound to a nitrogen atom. When combined, its molecular formula is C6H15N.

• The formula: C3H7-NH-C3H7 or C6H15N.
• The structure: CH3-CH2-CH2-NH-CH2-CH2-CH3.

The nitrogen in dipropylamine carries a single hydrogen atom, confirming its secondary classification due to one hydrogen replacement by each propyl group.
Dipropylamine can be found as a colorless liquid. It is often used across different sectors, including chemical manufacturing and pharmaceuticals, for its base properties and stable characteristics.

Butyldimethylamine

Butyldimethylamine is a tertiary amine, which means three carbon-containing groups surround the nitrogen atom. In this case, the nitrogen is bonded to one butyl group (C4H9) and two methyl groups (CH3). The molecular formula for butyldimethylamine is C6H15N, similar to dipropylamine.

• The formula: C4H9-N(CH3)2 or simply C6H15N.
• The structure: CH3-N(CH3)-CH2-CH2-CH2-CH3.

Tertiary amines like butyldimethylamine stand out due to their non-branched linear structure, which provides certain steric and electronic advantages in reactions.
This amine is often used in organic synthesis and as a catalyst due to its robust and distinct properties.

Triethylamine

Triethylamine represents a class of tertiary amines as well. It contains three identical ethyl groups (C2H5) attached to one nitrogen center, giving it the formula C6H15N.

• The formula: (C2H5)3N or C6H15N.
• The structure: CH3-CH2-N(CH2-CH3)-CH2-CH3.

Triethylamine's structure allows it to act as a strong organic base, making it invaluable in practical laboratory settings to deprotonate acids, among other applications.
Its relatively small and symmetrical shape gives it lower physical collision cross-sections with other molecules. This results in unique chemical reactions compared to non-tertiary amines. It is typically found as a pungent, colorless liquid with familiar applications in the manufacture of plastics and pharmaceuticals.