chem: Add isomers and benzene reactions

docs/snc4mz.md

@@ -174,10 +174,24 @@ As benzene rings do not have double bonds, they are named according to the **fir
 
 **Structural isomers** are two chemicals that have the same chemical formulas but have different structural formulas, resulting in different chemical properties.
 
+**Hydrocarbon chain isomers** are two chemicals with the same chemical formulas but have different carbon/hydrogen arrangements.
+
 !!! example
-    The following are two structural isomers of $\ce{C5H12}$.
+    The following are two hydrocarbon chain isomers (and, by extension, structural isomers) of $\ce{C5H12}$.
     <img src="/resources/images/structural-isomer-g5h12.png" width=700>(Source: Kognity)</img>
 
+**Positional isomers** are two chemicals with the same chemical formulas **and functional groups** but have different structural formulas.
+
+!!! example
+    The following are positional isomers (and, by extension, structural isomers) of $\ce{C4H8}$.
+    <img src="/resources/images/positional-isomers.png" width=700>(Source: Kognity)</img>
+
+**Functional group isomers** are chemicals with the same chemical formulas but **different functional groups**.
+
+!!! example
+    The following are functional group isomers (and, by extension, structural isomers) of $\ce{C3H6O2}$.
+    <img src="/resources/images/functional-group-isomers.png" width=700>(Source: Kognity)</img>
+
 **Geometric** or **cis/trans isomers** are two chemicals have the same chemical formulas and atom arrangements but are positioned differently, thus having ambiguous names.
 
 In order for this to occur, there must be two different atoms or groups of atoms bonded to each carbon atom in the double bond.
@@ -198,6 +212,59 @@ Unlike the examples below, these should be named with "cis" or "trans" at the be
     The following are cis-trans isomers of dichlorocyclobutane (notice the chlorine):
     <img src="/resources/images/cis-trans-ring.png" width=700>(Source: Kognity)</img>
 
+Isomers may have different physical properties in:
+
+ - **polarity**: a cis isomer may cause a molecule to be polar as opposed to its trans variant
+ - **packing efficiency**: a non-branching hydrocarbon chain will pack better than a branching one, and a continuously trans chain will pack better than a cis one
+
+These change the strength and type of intermolecular forces involved so affect their melting/boiling points.
+
+Isomers may also have different chemical properties as cis isomers are more likely to bump into themselves to make some reactions more viable
+
+### Benzene reactions
+
+!!! definition
+    - An **electrophile** is any species that is or would be electron deficient (+) in the presence of a pi bond.
+    
+In reactions involving a benzene ring, the ring itself is **stable** and will not break apart because of the strength of delocalised pi bonds.
+
+Therefore, only the hydrogens can be swapped out via **electrophilic substitution**, where an hydrogen atom is substituted with an electrophile. The concentration of electrons in the delocalised pi area attracts electrophiles to initiate the bond.
+
+In the mechanism diagram below, $\ce{E+}$ represents the electrophile. Curly arrows are used to show the movement of electrons from the **delocalised area to the electrophile** and **hydrogen atom to the delocalised area**.
+
+<img src="/resources/images/benzene-substitution-mechanism.png" width=900>(Source: Kognity)</img>
+
+The **first step** (the change from the first to the second diagram) is the **slow step** due to the highest activation energy due to the requirement to break a bond.
+
+<img src="/resources/images/benzene-substitution-mechanism-graph.png" width=900>(Source: Kognity)</img>
+
+#### Benzene nitration
+
+!!! definition
+    - A **nitrating mixture** is a mixture of concentrated sulfuric and nitric acids.
+
+In a **nitrating mixture**, benzene will react with positive nitronium ions at **~50°C** to form nitrobenzene, outlined in the reaction mechanism diagrams below.
+
+$$\ce{C6H6 + HNO3_{(aq)} ->[conc H2SO4][50^\circ C] C6H5NO2 + H2O_{(l)}}$$
+
+<img src="/resources/images/benzene-nitration-mechanism.png" width=900>(Source: Random Quora Person)</img>
+
+The first step is to **form the nitronium ion** through a Bronsted-Lowry acid-base reaction between the acids.
+
+$$\ce{HNO3_{(aq)} + H2SO4_{(aq)} <=> H2NO3+_{(aq)} + HSO4-_{(aq)}}$$
+
+The lone pair on the oxygen of the nitric acid attracts a hydrogen atom, which becomes an $\ce{H+}$ ion as sulfuric acid's oxygen takes its electrons. The hydrogen ion bonds to the nitric acid.
+
+$$\ce{H2NO3+_{(aq)} <=> H2O_{(l)} + NO2+_{(aq)}}$$
+
+The oxygen-hydrogen group is conveniently able to form water by taking both electrons it was sharing with the nitrogen. The other single-bonded oxygen compensates with a dative covalent bond with the nitrogen to form the nitronium ion.
+
+The second step is to **react with benzene** through electrophilic substitution, with electrons moving back from the dative oxygen-nitrogen bond back to the oxygen.
+
+### Alkane reactions
+
+### Alkene/yne reactions
+
 ## Resources
 
  - [IB Chemistry Data Booklet](/resources/g11/ib-chemistry-data-booklet.pdf)