1.12 Drawing Chemical Structures

Chemical structures are the language of organic chemistry. They reveal how atoms connect and interact. Skeletal structures simplify complex molecules, focusing on carbon backbones and key functional groups. This visual shorthand helps chemists communicate and analyze molecular properties efficiently.

Interpreting these structures is a crucial skill. By counting atoms, bonds, and identifying patterns, you can deduce molecular formulas and properties. Understanding how to draw and read chemical structures unlocks deeper insights into molecular behavior and reactivity.

Drawing Chemical Structures

Carbon-carbon bonds in skeletal structures

Top images from around the web for Carbon-carbon bonds in skeletal structures

• 

  Hydrocarbons | Chemistry: Atoms First View original

  Is this image relevant?

• 

  2.22: Carbon - Organic Molecules and Functional Groups - Biology LibreTexts View original

  Is this image relevant?

• 

  Organic chemistry 01: What is organic chemistry, drawing structures View original

  Is this image relevant?

• 

  Hydrocarbons | Chemistry: Atoms First View original

  Is this image relevant?

• 

  2.22: Carbon - Organic Molecules and Functional Groups - Biology LibreTexts View original

  Is this image relevant?

1 of 3

Top images from around the web for Carbon-carbon bonds in skeletal structures

• 

  Hydrocarbons | Chemistry: Atoms First View original

  Is this image relevant?

• 

  2.22: Carbon - Organic Molecules and Functional Groups - Biology LibreTexts View original

  Is this image relevant?

• 

  Organic chemistry 01: What is organic chemistry, drawing structures View original

  Is this image relevant?

• 

  Hydrocarbons | Chemistry: Atoms First View original

  Is this image relevant?

• 

  2.22: Carbon - Organic Molecules and Functional Groups - Biology LibreTexts View original

  Is this image relevant?

1 of 3

• Carbon atoms represented by ends of lines and vertices where lines meet
• Hydrogen atoms attached to carbon not shown explicitly
• Heteroatoms (O, N, S) and functional groups shown explicitly
• Double and triple bonds represented by double and triple lines respectively (ethene, ethyne)
• Skeletal structures simplify drawings by focusing on carbon backbone and functional groups (pentane, hexanal)
• Bond line notation is a common way to represent organic molecules in skeletal structures

Interpretation of skeletal structures

• Count number of carbon atoms (C) in skeletal structure
  • Each line end or vertex represents one carbon atom
• Determine number of hydrogen atoms (H) attached to each carbon atom
  • Each carbon atom assumed to have enough hydrogen atoms to make four total bonds
  • Subtract number of bonds to other atoms from four to determine number of hydrogen atoms (methane, ethane)
• Count number of heteroatoms (O, N, S) in structure
• Write molecular formula in format: $C_nH_mX_p$
  • n = number of carbon atoms
  • m = total number of hydrogen atoms
  • X = heteroatom symbol
  • p = number of heteroatoms (ethanol, propanamine)

Multiple structures for molecular formulas

• Determine number of carbon, hydrogen, and heteroatoms from molecular formula
• Identify degree of unsaturation (DU) or number of double bond equivalents (DBE)
  1. Calculate DU using formula: $DU = C - \frac{H}{2} + \frac{N}{2} + 1$
  2. Calculate DBE using formula: $DBE = \frac{2C + 2 - H - X + N}{2}$
     • C = number of carbon atoms, H = number of hydrogen atoms, N = number of nitrogen atoms, X = number of halogens
• Distribute carbon atoms in various possible arrangements
  • Linear, branched, or cyclic structures (butane, isobutane, cyclobutane)
• Add double or triple bonds to satisfy DU or DBE (1-butene, 1-butyne)
• Place heteroatoms and functional groups in different positions while maintaining correct number of bonds for each atom (butanol, butanamine)
• Ensure proposed structures satisfy given molecular formula and degree of unsaturation or double bond equivalents
• Consider isomers when proposing multiple structures for a given molecular formula

Advanced Structural Representations

• Wedge and dash notation is used to show three-dimensional arrangements of atoms
• Condensed structural formula provides a compact representation of molecular structure
• Stereochemistry describes the spatial arrangement of atoms in molecules
• Resonance structures show electron delocalization in molecules with multiple valid Lewis structures