finishing up on lesson 4

docs/lectures/organic-chemistry/lesson-4_24-09-2024.md

@@ -501,3 +501,88 @@ On the other hand, Cholesterol, with 27 carbon atoms and only one OH group, has
 | $\ce{CH3CH2CH2CH3}$   | insoluble (no N or O atom to hydrogen bond to $\ce{H2O}$) | soluble |
 | $\ce{CH3CH2CH2OH}$    | soluble ($\leq 5$ C's and an O atom for hydrogen bonding to $\ce{H2O}$) | soluble |
 | $\ce{CH3(CH2)10OH}$   | insoluble ($> 5$ C's; too large to be soluble even though it has an O atom for hydrogen bonding to $\ce{H2O}$) | soluble |
+
+### Vitamins
+
+Vitamins are organic compunds needed in small amounts for normal cell function, most cannot be synthesized in our bodies and must be obtained from diet. Most are identified by a letter, such as A, C, D, E and K.
+
+There are several different B vitamins, so a subscript is added just to distinguish between them. Examples are $\ce{B_1}$, $\ce{B_2}$ and $\ce{B_12}$.
+
+- Vitamins can be fat soluble or water soluble depending on their structure
+
+#### Vitamin A
+
+- Vitamin A is an essential component of the vision receptors in our eyes. Vitamin A or *retinol* may be obtained **directly from diet**.
+- It also can be obtained from the conversion of $\beta$-carotene, the orange pigment found in many plants including carrots, into vitamin A in our bodies.
+- Vitamin A is water insoluble because it contains only one OH group and 20 carbon atoms.
+
+<p align="center">
+    <img src="./assets/bcarotene-vitamin-a.png" width=400 />
+</p>
+
+#### Vitamin C
+
+- Vitamin C, ascorbic acid, is important in the formation of collagen. Most animals can synthesize vitamin C but Humans must obtain this vitamin from dietary sources, such as citrus fruits.
+
+- Each carbon atom is bonded to an oxygen which makes it capable of hydrogen bonding, and thus, water soluble.
+
+<p align="center">
+    <img src="./assets/vitamin-c.png" width=200 />
+</p>
+
+### Functional groups and electrophiles
+
+- All functional groups contain a heteroatom, a bond, or both.
+- These features create electrophilic sites and nucleophilic sites in a molecule.
+- **Electron-rich sites (nucleophiles)** react with **electron-poor sites (electrophiles)**.
+- An electronegative heteroatom like $\ce{N}$, $\ce{O}$, or $\ce{X}$ makes a carbon atom electrophilic, as shown below.
+
+<p align="center">
+    <img src="./assets/electrophilic-example.png" width=400 />
+</p>
+
+- In the examples, a partially positive carbon atom ($\delta^+$) is attached to an electronegative atom (like $\ce{Cl} or $\ce{OH}$), making the carbon **electrophilic** (electron-poor), which is susceptible to attack by nucleophiles.
+
+### Nucleophilic sites in moleucules
+
+A lone pair on a heteroatom makes it basic and nucleophilic
+
+<p align="center">
+    <img src="./assets/some-base-nucleophiles.png" width=400 />
+</p>
+
+$\pi$ bonds create nucleophilic sites and are more easily broken than $\sigma$ bonds.
+
+<p align="center">
+    <img src="./assets/nucleophiles-with-pibonds.png" width=400 />
+</p>
+
+An electron-rich carbon reacts with an electrophile, symbolized as $\text{E}^+$. For example, alkenes contain an electron-rich double bond, and so they react with electrophiles $\text{E}^+$.
+
+<p align="center">
+    <img src="./assets/pibond-nuclephile-reaction-electrophile.png" width=400 />
+</p>
+
+Alkyl halides possess an electrophilic carbon atom, so they react with electron-rich nucleophiles.
+
+<p align="center">
+    <img src="./assets/alkyle-halide-reaction-electro-nucleophile.png" width=400 />
+</p>
+
+#### Biomolecules
+
+- Biomolecules are organic compounds found in biological systems.
+- Many are relatively small, with molecular weights of less than 1000 g/mol.
+- Biomolecules often have several functional groups.
+
+#### Families of Biomolecules
+
+- There are four main families of small biomolecules:
+  - **Simple sugars**: combine to form complex carbohydrates like starch and cellulose
+  - **Amino acids**: join together to form proteins
+  - **Nucleotides**: combine to form DNA
+  - **Lipids**: commonly form from fatty acids and alcohols
+
+<p align="center">
+    <img src="./assets/example-biomolecules.png" width=400 />
+</p>