The lecture series provides a foundational understanding of chemical reactivity in organic chemistry.

Alkanes

The video series begin with alkanes. Students learn IUPAC nomenclature for naming straight-chain, branched, and cycloalkanes, including the importance of selecting the longest parent chain and numbering for the lowest substituent positions. The concept of constitutional isomers is reviewed, highlighting that different connectivity leads to different properties and stabilities. Alkane stability is quantitatively assessed through combustion analysis, where less heat released indicates greater stability. A significant portion covers conformational analysis using Newman projections to visualize rotations around single bonds and their associated energetic costs. Students analyze ethane (staggered vs. eclipsed), propane (CH-CH vs. CH-CH3 eclipsing), and butane (anti, gauche, syn conformers, and their relative stabilities due to steric interactions). The discussion extends to cycloalkanes, explaining angle strain (deviation from ideal 109.5° tetrahedral angles) and torsional strain (eclipsing bonds), which are significant in smaller rings like cyclopropane and cyclobutane. Cyclohexane is presented as a unique cycloalkane with minimal strain in its chair conformation. Students learn to draw chair conformers, identify axial and equatorial positions, understand ring flips (where axial becomes equatorial and vice versa), and rationalize stability differences between conformers, particularly due to unfavorable 1,3-diaxial interactions which are essentially gauche interactions within a ring.

Reactivity

The series then delves into reactivity, defining most organic reactions as ionic processes involving nucleophiles (electron-rich Lewis bases that donate electron pairs) and electrophiles (electron-deficient Lewis acids that accept electron pairs). A crucial skill taught is arrow pushing, using curved arrows to depict electron flow in four fundamental mechanistic patterns: nucleophilic attack (nucleophile forming a bond with an electrophile), loss of a leaving group (bond dissociation where a group leaves with its electrons), proton transfers (acid-base reactions), and rearrangements, focusing on carbocation rearrangements. The stability of carbocations is explained by hyperconjugation (tertiary > secondary > primary > methyl), leading to hydride and alkyl shifts that occur when a more stable carbocation can be formed. Additionally, the lectures provide a comprehensive review of thermodynamic quantities, including enthalpy (ΔH) for heat released/absorbed (exothermic vs. endothermic reactions), entropy (ΔS) for disorder (contributions from the system and surrounding), and Gibbs free energy (ΔG) for reaction spontaneity (exergonic vs. endergonic) and its relationship to equilibrium position. Kinetic principles are also revisited, emphasizing activation energy (EA) as a determinant of reaction rate, and students learn to interpret reaction coordinate diagrams to assess both kinetic (rate) and thermodynamic (product stability) favorability.

Acids and Bases

Finally, the series establishes the principles of acid-base reactions, beginning with the definitions of Brønsted-Lowry acids and bases (proton donors/acceptors) and the broader Lewis acids and bases (electron pair acceptors/donors). A key focus is on drawing reaction mechanisms using curved arrows to illustrate electron movement during proton transfer. Students learn to identify conjugate acids and bases. Acid strength is quantitatively determined using Ka and pKa values, where a smaller pKa indicates a stronger acid. Qualitatively, acid strength and equilibrium position are predicted by assessing the stability of the conjugate base. Four key factors influence conjugate base stability, in order of priority: the atom bearing the charge (electronegativity in the same row, size in the same column), resonance (delocalization of the electron pair), induction (electron withdrawal by adjacent electronegative atoms), and the orbital in which the electron pair resides (sp > sp2 > sp3 due to proximity to the nucleus).

Student Learning Outcomes

• Name simple alkanes, including branched and cycloalkanes.

• Determine relative stability of alkanes using combustion analysis.

• Draw and interpret Newman projections.

• Sketch conformational analysis of simple alkanes (ethane, propane, butane).

• Rationalize the relative stability of cycloalkanes (angle and torsional strain).

• Draw chair conformers of cyclohexanes.

• Identify axial and equatorial positions on cyclohexanes.

• Draw ring-flipped conformers of cyclohexanes.

• Rationalize stability differences between ring-flipped conformers (1,3-diaxial interactions).

• Review and understand thermodynamic quantities (ΔS, ΔH, ΔG, Keq).

• Review and understand kinetic properties (K, EA).

• Interpret reaction coordinate diagrams to determine kinetic and thermodynamic favorability.

• Define and identify nucleophiles and electrophiles.

• Draw and identify common arrow-pushing mechanism patterns (nucleophilic attack, loss of a leaving group, proton transfers, rearrangements) in organic chemistry reactions.

• Identify Brønsted-Lowry acids and bases and draw mechanisms of acid-base reactions.

• Use quantitative (Ka, pKa) and qualitative (base stability factors like atom, resonance, induction, orbital) values to determine acid strength and predict the position of acid-base equilibrium.

• Identify counterions in reactions involving anionic bases.