Lecture Notes on Arrows in Organic Chemistry

Using interactive models (physical or digital) can be good for picturing stereochemistry.
MoleView:
- A website where you can draw molecules and render them in 3D.
- Useful for determining R/S configurations by allowing you to spin the molecule around.
- Example: Alanine
  - Drawing alanine in MoleView allows you to visualize and determine if it's R or S.
  - In the example given, alanine is in the S configuration (anti-clockwise: NH2, COOH, CH3).

Shifting focus from naming, biological molecules, and structure to reactivity.
The goal is to start "making things".
Organic chemistry is crucial because almost everything synthetic is made through organic reactions.
Focus on understanding the types of reactions used to build everyday chemicals.

Most commodity chemicals are synthesized from petroleum.
Crude oil cracking yields chemicals used in manufacturing.
Double bonds in alkenes are a significant source of reactivity, allowing for the addition of functional groups.
Alkenes are the "gateway" to much synthetic chemistry.
Examples: Ethylene and propylene are starting points for many chemicals.
Implications: Plastic and plastic waste will be discussed later.

Functionality in the body (secondary metabolites) arises from the reactivity of double bonds.
The body uses double bonds to attach and detach molecules, modifying their functionality.
Examples: Pheromones and cholesterol all contain reactive double bonds.

Example Molecule:
- A molecule with a triple bond.
- Task: Name the molecule.
Steps:
- Identify the longest carbon chain containing the triple bond (hexane = six carbons).
- Number the chain to give the triple bond the lowest possible number (2-hexyne).
- Identify and name any substituents (5-methyl).
- Full name: 5-methylhex-2-yne or 5-methyl-2-hexyne.

Electrophile: An atom that is "looking" for electrons (electron-loving).
Nucleophile: An atom with excess electrons to donate; looking for a nucleus.
Reaction: Electrophile (+) reacts with Nucleophile (-) to form a covalent bond.
Key Point: The movement of two electrons forms a covalent bond.
Alkenes as Nucleophiles: Alkenes are good nucleophiles because they have electrons to donate.

These arrows represent the movement of two electrons.
If you understand the language of arrows, you can discover chemistry for yourself.
Rules for drawing arrows:
- The arrow begins at electrons, either:
  - Lone pair of electrons.
  - Sigma bond.
  - Pi bond.
- The arrow terminates in:
  - Creation of a lone pair.
  - Formation of a sigma bond.
  - Formation of a pi bond.

Example 1: Movement of electrons from an O-H sigma bond to oxygen.
- Result: Negatively charged oxygen (lone pair) and positively charged hydrogen.
Example 2: Movement of electrons to create a C-H bond.
- Result: Lithium becomes Li+ because it lost its electron.
Example 3: Formation of a double bond.
- Result: Loss of H+.
Infographic Summary: There are eight types of mechanistic arrows.

Arrows Must Start at Electrons:
- Arrows show the movement of electrons, not positive charges.
- Start at lone pairs, sigma bonds, or pi bonds.
Electrons in Bonds:
- Two electrons in each double bond.
- Two electrons in each single bond.
- Two electrons in each lone pair.
Charge Changes:
- Removing electrons leaves a positive charge.
- Moving to a lone pair neutralizes a positive charge or adds a negative charge.
Octet Rule:
- Never violate the octet rule (carbon cannot have more than four bonds).
- Pentavalent carbons are not allowed.

Focus: Learning how arrows work without needing chemistry knowledge.
Example 1:
- Arrows indicate a new bond from oxygen to carbon, loss of a double bond, and loss of Cl-.
- Following the arrows allows you to draw the product.
Example 2:
- Lone pair from nitrogen forms a new bond, resulting in a positive charge on nitrogen.
- Resulting in a Cl- because the electrons that were in this bond now reside entirely on the chlorine.
Example 3:
- Electrons from the double bond move to the oxygen, creating a lone pair.
- The oxygen will have a formal charge of -one.

Example 1: Creating H+ and Cl- from HCl.
- Arrow: Movement of the two electrons from the single bond to the chlorine.
Example 2: Forming H+ and OH-.
- Arrow: Movement of two electrons from the O-H bond onto the oxygen.
Product Prediction: Given the arrow, draw the product.
- Example: Two electrons moving onto the oxygen.
- Result: Oxygen with a negative charge and H+.

How many H's are there on this carbon?
First Carbon: This carbon is connected to two H's
Second Carbon: This carbon is only connected to one H because it has a positive charge, meaning it has less electrons than normal
The Arrow: the electrons from that C H bond migrate across to this carbon forming a new C H bond.

If I show you the arrows can you see now how to draw the products?
- The electrons from the pi bonds are now connecting this top carbon to this hydrogen which makes this second bond the double bond be lost.
- Those electrons are going onto the chlorine, and because chlorine now a formal charge of negative one will be negative.
- This carbon lost the shared electron when this double bond went to create this new single bond so he's going to be positively charged.
2nd step: Take the intermediate, and electrons from Chlorine moves to create a covalent bond.
Here's the two electrons for this chlorine and here's the product.
Addition Reaction: the H and the Cl get added across the double bond

Following arrows to predict products without prior chemistry knowledge.
Importance of Balancing Charges: Total charge should be the same on both sides of the arrow.

Understand the movement of two electrons and follow the set of rules:
We are going to talk about how double bonds can react with molecules like $HCl$ or $H<em>2O$ $H</em>2$ to add both sides of the double bond.
- If I had a different color, these two electrons connecting the H and the X forming another bond. This allows us to access alcohols. It allows us to access dihalogenated compounds and halogenated compounds and this is the entry point now to organic chemistry.
In the next lecture, There are conditions that will do the reverse reaction that will take an alkyl halide or an alcohol back to an LP *We are going to focus on the forward reaction, the additions reactions as that's really the entry point into organic chemistry
Practice is Essential: You need to be able to understand the movement of two electrons at this set of rules to fully understand organic chemistry in the next few lectures.