Chem Oct. 8th

Organic reactions are often taught in a rote memorization fashion which may not be effective for understanding organic chemistry (often abbreviated as Orgo).
The course aims to foster understanding of functional groups and the reactions they undergo through a deeper look into the movement of electrons in reactions.
An emphasis will be placed on building chemical intuition rather than rote memorization.

The textbook organizes reactions by functional groups, but similar reaction types can occur across different groups.
Students will learn to recognize patterns between reactions covered in earlier sections and those introduced later in the curriculum.
Understanding reaction mechanisms involves familiarity with reagents and predicting reaction products.

Focus on two classes of reactions: substitution and elimination.
- Substitution Reactions: The nucleophile attacks the electrophile, leading to the replacement of a leaving group (often denoted as 'X').
- Elimination Reactions: Removal of leaving groups leading to unsaturated products (double bonds).

Reagents: Reactants used in a chemical reaction, typically written next to the reaction arrow in organic equations.
Nucleophile: A species that donates an electron pair to form a chemical bond. The term comes from "nucleus-loving," as nucleophiles are attracted to positively charged centers.
Electrophile: An electron-deficient species that accepts an electron pair.
Leaving Group: The atom or group that departs with a pair of electrons in a substitution or elimination reaction, contributing to the formation of a new bond.

The reactivity of alkyl halides will be analyzed to predict product distributions, which may be influenced by sterics and electronic effects.
Alkyl halides typically feature halogens like Cl, Br, and I as leaving groups; fluorine behaves differently due to stronger bonds and poor leaving group ability.

Case Study: 2-Chloropropane With Sodium Hydroxide
- The reactions result in substitution (formation of an alcohol) and elimination (production of an alkene).
Understanding the distribution of products will rely on recognizing minor versus major products in reaction outcomes.

When drawing organic structures, it's essential to indicate the partial positive (δ+) and partial negative (δ−) charges that arise due to polar bonds.
- e.g. In alkyl halides, the carbon-halogens bonds create a polarized bond due to the electronegativity difference.
The stability of leaving groups is critical, with halogens being stable enough conjugate bases to promote their departure in reactions.
Examining Stability: Differences in leaving group stability directly relate to their base strength; weaker bases make better leaving groups.
- Example: I− is a better leaving group than OH− due to its greater stability.

Substitution Reaction Overview: In both types of substitutions, nucleophiles interact with electrophiles to generate new products.
Steps Involved in Sne2: This involves a single, concerted step with a backside attack that results in inversion of stereochemistry.
- Nucleophiles will typically attack the least hindered side of the electrophile due to sterics.
- SN2 reactions have two species involved in the rate-determining step (alkyl halide and nucleophile).

The reaction can be visualized through diagrams demonstrating nucleophile attack and leaving group departure with arrows to show electron flow.
Use of stereochemical configurations where the configuration of the product will depend on whether it progresses through the front or back of the electrophile.

Understanding configurations (R/S designations) helps predict how reactants convert into products, specifically in SN2 reactions where configuration inversion occurs.
Depending on the original stereochemistry of the substrates, the product formed will have its configuration inverted due to the nature of backside attacks.

Nucleophile Strength: Strength correlates with charge; more negatively charged nucleophiles react faster than neutral ones.
Sterics: Increasing steric hindrance around the electrophilic center can significantly slow down nucleophilic attacks.
Reaction rate comparisons show that tertiary alkyl halide reactions may not proceed through SN2 pathways due to steric hindrance while being more favorable for SN1 pathways due to carbocation stability considerations.

Students will gain an understanding of the balance of nucleophiles and leaving groups when determining reaction pathways.
Further exploration of mechanistic details, particularly the SN1 mechanisms, will be a primary focus in subsequent sessions, contrasting with the SN2 pathway.