The lecture series provides a foundational understanding of ionic reactions at pi bonds in organic chemistry. The video series cover the reactivity of organic compounds, focusing on alkenes, conjugated pi bonds, alkynes, aromatics, and carbonyls. Students will gain the ability to predict products, propose reagents, and outline reasonable mechanisms for a wide array of reactions. This includes understanding regiochemical and stereochemical outcomes, particularly in addition reactions.

Addition to Alkenes, Conjugated Dienes, and Alkynes

The segment on alkenes details various addition reactions, including hydrohalogenation (Markovnikov, carbocation intermediates, prone to rearrangement), acid-catalyzed hydration (similar carbocation mechanisms, susceptible to rearrangement), and its non-rearranging alternative, oxymercuration-demercuration (Markovnikov addition via mercurinium ion). Other additions covered are hydroboration-oxidation (anti-Markovnikov, syn-addition), catalytic hydrogenation (syn-addition), halogenation and halo-hydrin formation (anti-addition via cyclic halonium ions), and dihydroxylation (anti- via epoxide or syn- via OsO4/KMnO4). Ozonolysis is presented as a method for oxidative cleavage of double bonds. For conjugated pi bonds, electrophilic addition leads to resonant-stabilized allylic carbocations, yielding both 1,2- and 1,4-adducts. The discussion highlights kinetic control (low temperature, favors faster 1,2-adduct) versus thermodynamic control (high temperature, favors more stable product). Alkynes undergo similar additions, often twice, for hydrohalogenation and halogenation. Their unique hydration reactions produce unstable enols, which rapidly convert to more stable ketones or aldehydes through keto-enol tautomerization.

Aromatic Substitutions on Benzene Rings

The lectures on aromatics focus on electrophilic aromatic substitution (EAS), explaining the role of strong electrophiles and the sigma complex intermediate. Students learn to identify and apply substituent effects, understanding why groups are activators or deactivators, and how they direct new substitutions to ortho/para or meta positions. Steric effects and the use of blocking groups (like the sulfonate group) are introduced as synthetic tools to control regioselectivity. Beyond EAS, the videos introduce nucleophilic aromatic substitution (SNAr), which requires strong nucleophiles, good leaving groups, and electron-withdrawing groups in specific positions, proceeding via a Meisenheimer complex. An alternative, the elimination-addition (benzyne mechanism), is discussed for conditions not suitable for SNAr.

Additions and Substitutions on Carbonyl Compounds

Finally, carbonyls chemistry is explored through nucleophilic addition reactions to aldehydes, ketones, and carboxylic acid derivatives. Aldehydes and ketones form hydrates, acetals, imines, and enamines with oxygen and nitrogen nucleophiles, and undergo reductions (with hydrides) and reactions with Grignard reagents or Wittig reagents (carbon nucleophiles). The reactivity of carboxylic acid derivatives (acid chlorides > anhydrides > esters > amides) dictates their synthesis and reactions, primarily nucleophilic acyl substitution. Preparation methods and diverse reactions, including hydrolysis, alcoholysis, aminolysis, and various reductions (complete or partial using selective reagents), are detailed for these functional groups, along with nitriles.

Student Learning Outcomes

• Alkenes:

  • Apply thermodynamic principles to determine the favorability of alkene addition reactions and rationalize regiochemical and stereochemical outcomes.

  • Propose arrow pushing mechanisms for various addition reactions, including hydrohalogenation.

  • Predict products and propose mechanisms for acid-catalyzed hydrations, and understand the advantages of oxymercuration-demercuration to avoid rearrangements.

  • Identify synthetic tools for anti-Markovnikov hydration (hydroboration-oxidation), explain its regiochemical and stereochemical outcomes, and propose mechanisms.

  • Predict products and stereochemical outcomes for catalytic hydrogenations (syn-addition).

  • Draw and identify mechanisms for anti-addition reactions like halogenation, halo-hydrin/halo-ether formation, and anti-dihydroxylation, identifying electrophiles and nucleophiles involved.

  • Predict products and show stereochemical outcomes for syn dihydroxylation and ozonolysis.

• Alkynes:

  • Understand and apply addition reactions (hydrohalogenation, halogenation, ozonolysis) to alkynes, noting similarities and differences to alkenes.

  • Describe and propose mechanisms for the unique hydration reactions of alkynes, including the formation of unstable enols and their rapid tautomerization to ketones or aldehydes.

• Conjugated Pi Bonds:

  • Predict the products of electrophilic addition reactions to conjugated dienes.

  • Explain the effect of temperature on the outcome of electrophilic additions to conjugated dienes, differentiating between kinetic and thermodynamic control.

• Aromatics:

  • Predict products, propose reagents, and outline reasonable mechanisms for electrophilic aromatic substitutions (EAS) to benzene.

  • Incorporate reduction chemistry after EAS to synthesize primary alkyl and amino groups on benzene.

  • Predict the major products of EAS involving monosubstituted and polysubstituted benzene rings.

  • Explain why groups are activators or deactivators for EAS, and why activators are ortho/para-directing while deactivators are meta-directing.

  • Utilize directing effects, steric effects, and blocking groups in proposing synthetic pathways for polysubstituted benzene rings.

  • Differentiate between electrophilic aromatic substitution, nucleophilic aromatic substitution (SNAr), and elimination-addition (benzyne) reactions, and propose mechanisms for SNAr and elimination-addition reactions.

• Carbonyls:

  • Predict products and propose mechanisms for nucleophilic additions of oxygen nucleophiles to aldehydes and ketones (forming hydrates, hemiacetals, and acetals), and for their subsequent hydrolysis.

  • Predict products and propose mechanisms for nucleophilic additions of nitrogen nucleophiles to aldehydes and ketones (forming carbinolamines, imines, and enamines), and for their hydrolysis.

  • Predict products and propose mechanisms for the reduction of aldehydes and ketones using hydrogen nucleophiles.

  • Prepare and utilize powerful carbon nucleophiles, such as Grignard reagents and Wittig reagents, in nucleophilic additions to aldehydes and ketones.

  • Prepare acid chlorides from carboxylic acids, detailing the mechanism and necessary reagents, and predict reactions of acid chlorides with various nucleophiles.

  • Devise different methods for preparing esters, and predict the products and mechanisms of ester reactions with various nucleophiles.

  • Prepare amides and nitriles, and predict their limited scope of reactions, including hydrolysis and reduction.