Intermolecular Forces of Attraction (ORGCHEM 2024) Lecture Notes PDF

SLRM2024 1 PH-BPS 114 Lecture: INTERMOLECULAR FORCES OF ATTRACTION Slides prepared by: Ser Loisse R. Mortel QUESTIONS: Why does alcohol evaporate faster than water? Why doesn’...

SLRM2024 1 PH-BPS 114 Lecture: INTERMOLECULAR FORCES OF ATTRACTION Slides prepared by: Ser Loisse R. Mortel QUESTIONS: Why does alcohol evaporate faster than water? Why doesn’t oil mix with water? SLRM2024 INTER vs INTRA Between separate molecules, opposites attract. The more opposite, the more attraction SLRM2024 SLRM2024 SLRM2024 TYPES IMPORTANT FOR ORGANIC CHEM London Dispersion Forces/ “Van der Waals” Dipole-dipole Hydrogen bond Ion-dipole Ion-ion SLRM2024 London DISPERSION forces SLRM2024 London DISPERSION forces SLRM2024 Dipole-dipole (dd) – due to permanent dipoles between 2 molecules Hydrogen bond – dipole-dipole where the + dipole comes from H (OH, NH, FH) SLRM2024 H-bonds are stronger IMFs than regular dipole-dipole bonds. © AstroGate Science SLRM2024 SLRM2024 FACTORS THAT AFFECT IMF Dipoles increase the POLARITY More carbons = less polar More electronegative atoms – more polar (OH, NH even more) Contact area/surface area affects the QUANTITY Affected by the stacking of molecules Linear – good stacking – abundance in IMF Branched – reduced stacking – decrease in IMF SLRM2024 FACTORS THAT AFFECT IMF Dipoles increase the POLARITY More carbons = less polar More electronegative atoms – more polar (OH, NH even more) SLRM2024 FACTORS THAT AFFECT IMF Dipoles increase the POLARITY More carbons = less polar More electronegative atoms – more polar (OH, NH even more) SLRM2024 FACTORS THAT AFFECT IMF Contact area/surface area affects QUANTITY Affected by the stacking of molecules Linear – good stacking – abundance in IMF Branched – reduced stacking – decrease in IMF SLRM2024 When comparing different functional groups: Stronger IMF (more charges) – ↑ When comparing similar functional groups: First tiebreaker: More carbons – more London dispersion - ↑ Second tiebreaker: Branching – less IMF – ↓ PRACTICE: Arrange by decreasing water solubility SLRM2024 FACTORS THAT AFFECT IMF Linear – good stacking – abundance in IMF Branched – reduced stacking – decrease in IMF Boiling point/ melting point/ density - related to strength of the IMFs per molecule When comparing different functional groups: Stronger IMF – ↑ When comparing similar functional groups: First tiebreaker: More carbons – more nonpolar bonds - ↑ Second tiebreaker: Branching – less IMF – ↓ SLRM2024 Boiling point/melting point/density - related to strength of IMF When comparing different functional groups: Stronger IMF – ↑ When comparing similar functional groups: First tiebreaker: More carbons – more nonpolar bonds - ↑ Second tiebreaker: Branching – less IMF – ↓ SLRM2024 Boiling point/melting point/density - related to strength of IMF When comparing different functional groups: Stronger IMF – ↑ When comparing similar functional groups: First tiebreaker: More carbons – more nonpolar bonds - ↑ Second tiebreaker: Branching – less IMF – ↓ SLRM2024 Boiling point/melting point/density - related to strength of IMF When comparing different functional groups: Stronger IMF – ↑ When comparing similar functional groups: First tiebreaker: More carbons – more nonpolar bonds - ↑ Second tiebreaker: Branching – less IMF – ↓ SLRM2024 Boiling point/melting point/density - related to strength of IMF When comparing different functional groups: Stronger IMF – ↑ When comparing similar functional groups: First tiebreaker: More carbons – more nonpolar bonds - ↑ Second tiebreaker: Branching – less IMF – ↓ PRACTICE: Arrange by decreasing boiling point A) Butane B) Butan-2-ol C) 2-methylpropane D) Propan-1-ol E) Butan-1-ol SLRM2024 GOING BACK: Why does alcohol evaporate faster than water? Why doesn’t oil mix with water?