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geometry: a4paper, margin=2cm 
header-includes:
- \usepackage{mhchem}
- \usepackage{chemfig}
- \usepackage{tabularx}
- \usepackage{gensymb}
---

# Organic Chemistry

Large number of compounds due to:

- 4 valence pairs
- single / double / triple bonds
- cyclic (ring) structures

## Properties of hydrocarbons

- *Saturated* - all C-C bonds are single
- Insoluble in water
- Almost non-polar (similar electronegativities)
- Only dispersion forces (valence e-)
- Dispersion forces increase with length
- Branched molecules have lower density

## Linear (aliphatic)

Alkanes: \ce{C_{$n$} H_{$2n+2$}}  
Alkenes: \ce{C_{$n$} H_{$2n$}}  
Alkynes: \ce{C_{$n$} H_{$2n-2$}}

## Naming hydrocarbons

- Branches end with _-yl_
- Indicate number of branches with di-, tri- etc.
- Longest unbranched carbon chain includes function group

## Functional groups

\setchemfig{atom sep=2em}
\renewcommand{\arraystretch}{3}
\begin{tabularx}{0.5\textwidth}{rlX}
  \hline
  Alcohols & \ce{-OH} & \chemfig{{\color{blue}R}-OH}\\\hline
  Esters & \ce{-OCO-} & \chemfig{{\color{blue}R}-C(=[:-30]O)-[:30]O-{\color{blue}R}}\\\hline
  Aldehydes & \ce{-CHO} & \chemfig{{\color{blue}R}-C(-[:-30]H)=[:30]O}\\\hline
  Ketones & \ce{-CO-} & \chemfig{C(-[:150]{\color{blue}R})(-[:-150]{\color{blue}R})=O}\\\hline
  Carboxylic acids & \ce{-COOH} & \chemfig{{\color{blue}R}-C(=[:-30]O)-[:30]O-H}\\\hline
  Ethers & \ce{-O-} & \chemfig{{\color{blue}R}-[:210]O-[:-30]{\color{blue}R}}\\\hline
  Amines & \ce{-NH2} & \chemfig{{\color{blue}R}-N(-[:-30]H)(-[:30]H)}\\\hline
  Amides & \ce{CO-NH} & \chemfig{{\color{blue}R}-[:30]C(=[:90]O)-[:-30]N(-[:30]H)(-[:-30]H)}\\\hline
\end{tabularx}


## Isomers

* **Structural isomers** - same molecular formula, different arrangement
- **Positional isomers** - different position of functional group (affects polarity)
- **Chain isomers** - affects boiling point (more branches $implies$ lower boiling point)
* **Stereoisomers** - same structural configuration, different orientation  
  * **Optical/chiral isomers (enantiomers)** - chiral centre, 4 groups bonded to C, non-superimposable mirror image. Racemic mixture: 50/50 of each enantiomer. Affects optical polarity of light.
  * **Geometric isomers** - \ce{C=C} double bond, 2 groups bonded to carbon atoms
    + **Cis** - same horizontal plane (symmetrical)
    + **Trans** - diagonal (asymmetrical)

\begin{center}\setlength\tabcolsep{1cm}
\begin{tabularx}{0.5\textwidth}{cc}
  cis & trans \\
  \chemfig{[:60]{\text{\color{blue}R$^\prime$}}-C(-[:120]{\text{\color{red}R}})=[0]C(-[:-60]{\text{\color{blue}R$^\prime$}})-[:60]{\text{\color{red}R}}} &
  \chemfig{[:60]{\text{\color{blue}R$^\prime$}}-C(-[:120]{\text{\color{red}R}})=[0]C(-[:-60]{\text{\color{red}R}})-[:60]{\text{\color{blue}R$^\prime$}}}
\end{tabularx}\end{center}

## Flash point

Lowest temperature at which the liquid gives off enough vapour to be ignited. Flammable $\implies$ flash point > 37.8 \degree C.

## Reactions

**Cracking** - split moluecules with heat/pressure/catalyst

### Alkanes

- Relatively inert
- Non-polar solvent
- Non-soluble in \ce{H2O}
- Combusts in \ce{O2} (forms \ce{CO2 + H2O})
- Reacts with halogens (**substitution** of \ce{H})

### Alkenes

- More reactive than alkanes
- **Addition reactions**: \ce{C=C} bond is broken (energy released)
- **Addition polymerisation**

### Alcohols

- Can be formed from haloalkane substitution reaction
- **Oxidation** (combustion)
- Oxidation state $\propto$ no. of atoms connected to \ce{C}
- **Substitution** of functional group, e.g. \ce{ROH + NH3 -> RNH2 + H2O}
- Primary alcohols oxidise to aldehydes then carboxylic acids
- Secondary alcohols oxidise to ketones

### Carboxylic acids

- Weak acids
- **Hydrolysis**: \ce{RCOOH + H2O <=> RCOO^{-} + H2O^{+}}
- Rxn with amines - carboxylic acid + amine $\rightarrow$ ammonium salt $\rightarrow$ amide + water

### Esterification

- **Condensation reactions** (esterification): \ce{RCOOH + R^{$\prime$}OH -> RCOOR^{$\prime$} + H2O}
- This is reversed by **hydrolysis**: ester + water $\rightarrow$ carboxylic acid + alcohol
- Polyesters

## Summary of reactions

\textbf{Combustion:} \ce{C_{$x$} H_{$y$} + $z$O2 -> $x$CO2 + {$\dfrac{y}{2}$} H2O} \quad where $z=x+\dfrac{y}{4}$

\textbf{Substitution:} e.g. halogenation/chlorination, catalysed by UV (alkanes) or compounds (alcohols etc.) which creates free radicals (unpaired e-)

\textbf{Addition:} \ce{C=C} bond is broken, catalyst is required

\textbf{Addition polymerisation:} uses addition to form a polymer

\textbf{Condensation polymerisation:} produces \ce{H2O}

\textbf{Oxidation:} occurs in alcohols to form aldehydes with catalysts \ce{H+/MnO4- (aq)} or \ce{H+/Cr2O7{2-} (aq)} - see combustion equation

\textbf{Cracking:} heat/pressure/catalyst to break molecules