Large Moleclues Polar & Nonpolar

Molecule Polarity Overview

  • Nonpolar and Polar Molecules

    • For single atoms, they are always nonpolar.

    • For diatomics, it depends on whether the atoms are the same or different.

    • For molecules with three or more atoms, knowledge of molecular shape is necessary to determine polarity.

    • Larger molecules may lack a fixed shape.

Importance in Organic Chemistry

  • Many molecules related to food chemistry are large organic molecules (carbon-based).

  • Understanding polarity is essential for significant organic compounds.

Identifying Nonpolar Hydrocarbons

  • Hydrocarbons (composed solely of C and H) are always nonpolar.

    • Examples include:

      • Decane (large)

      • Methane (small)

  • The remaining atoms (often O, N, or F) can make the molecule polar.

    • Particularly, O (oxygen) and N (nitrogen) are critical in assessing polarity.

Polarity Comparison Calculation

  • For larger molecules, compare the number of polar atoms (O, N, F) with carbon atoms:

    • The polarity contribution of the polar part is multiplied by 3 when evaluating.

    • Consider the strength of polar versus nonpolar parts to determine overall polarity.

Examples of Polarity Determination

  1. C7H6O2 (Carbon-based organic)

    • O's: 2

    • Polar value: 2 × 3 = 6

    • C's: 7 (Winners: Nonpolar)

    • Result: Nonpolar and not soluble in water.

  2. C2H4O2

    • O's: 2

    • Polar value: 2 × 3 = 6

    • C's: 2 (Winners: Polar)

    • Result: Polar and soluble in water.

  3. C6H14O

    • O's: 1

    • Polar value: 1 × 3 = 3

    • C's: 6 (Winners: Nonpolar)

    • Result: Nonpolar and not soluble.

  4. C12H22O11 (Table sugar)

    • O's: 6

    • Polar value: 6 × 3 = 18

    • C's: 12 (Winners: Polar)

    • Result: Polar and soluble in water.

Practice Challenge

  • Identify polarity and solubility for the following:

    • Cholesterol:

      • O: 1 × 3= 3

      • C: More (Result: Nonpolar, not soluble)

    • Asparagine:

      • O's + N's: 7 × 3 = 21

      • (Result: Polar, soluble)

    • Urea:

      • O: 1 × 3 = 3 (and N's: 2 × 3 = 6)

      • (Result: Polar, soluble)

Hydrocarbon Structure Recognition

  • When examining line-angle structures:

    • Identify nonpolar hydrocarbon parts (C and H only) and polar functional groups (containing N, O).

  • Example structures include:

    • Fatty Acids with dominant nonpolar hydrocarbon parts and polar ends (usually O or N)

    • The overall polarity is determined by assessing both nonpolar and polar sections within large structures.