Draw Lewis structures for the acetonitrile molecule (CH3CN), the methylamine molecule (CH3NH2), and the methanimine molecule (CH2NH), and then answer the questions that follow.

/ Exams & Certification / By

Draw Lewis structures for the acetonitrile molecule (CH3CN), the methylamine molecule (CH3NH2), and the methanimine molecule (CH2NH), and then answer the questions that follow.

(Draw one structure per sketcher box, and separate added sketcher boxes with the + sign. Do not include overall ion charges or formal charges in your drawing. Do not draw double bonds to oxygen unless they are needed in order for the central atom to obey the octet rule.)

The Correct Answer and Explanation is:

Let’s analyze and draw the Lewis structures for the three given molecules: acetonitrile (CH₃CN), methylamine (CH₃NH₂), and methanimine (CH₂NH). Below is a detailed explanation and the corresponding structures.

1. Acetonitrile (CH₃CN)

Lewis Structure:

H   H   H
 \  |  /
  C — C ≡ N
     |
  • Carbon 1 (C in CH₃) is bonded to three hydrogens and one carbon.
  • Carbon 2 (C in CN) is triple bonded to nitrogen and single bonded to the CH₃ group.
  • Nitrogen has one lone pair and is triple bonded to the second carbon.

2. Methylamine (CH₃NH₂)

Lewis Structure:

H   H   H
 \  |  /
  C — N — H
     |
     H
  • Carbon (C) is bonded to three hydrogens and one nitrogen.
  • Nitrogen (N) is bonded to the carbon and two hydrogens and has one lone pair.

3. Methanimine (CH₂NH)

Lewis Structure:

H   H
 \  /
  C = N — H
     |
  • Carbon is bonded to two hydrogens and double bonded to nitrogen.
  • Nitrogen is bonded to carbon and one hydrogen and has one lone pair.

🧪 Explanation (300+ words):

Valence Electron Considerations:

To draw Lewis structures, you need to:

  1. Count valence electrons for each atom.
  2. Satisfy the octet rule (or duet for hydrogen).
  3. Connect atoms logically (least electronegative at the center, typically carbon).

1. CH₃CN – Acetonitrile

  • Total valence electrons:
    • C (4) × 2 + H (1) × 3 + N (5) = 16 electrons
  • Carbon in CH₃ forms three C-H bonds and one C-C bond.
  • The second carbon (connected to nitrogen) forms a triple bond with nitrogen to satisfy both their octets.
  • Nitrogen ends with one lone pair.

2. CH₃NH₂ – Methylamine

  • Total valence electrons:
    • C (4) + N (5) + H (1) × 5 = 14 electrons
  • Carbon bonds to three H and one N.
  • Nitrogen bonds to carbon and two Hs, and has one lone pair.
  • All atoms satisfy the octet (or duet for H).

3. CH₂NH – Methanimine

  • Total valence electrons:
    • C (4) + N (5) + H (1) × 3 = 12 electrons
  • Carbon forms two bonds with H and a double bond with N.
  • Nitrogen forms a double bond with C and one bond with H, with one lone pair.
  • Octets/duets are satisfied.

Conclusion:

These structures show the diversity of bonding in organic molecules:

  • CH₃CN includes a triple bond (C≡N),
  • CH₃NH₂ is a saturated amine,
  • CH₂NH has a C=N double bond (an imine).

Related Posts

Scroll to Top