Unit 1: Organic Nomenclature & Structure

Homologous Series

• Organic chemistry is the study of carbon-containing compounds

  • Eg: butane

    • molecular formula: C₄H₁₀

    • empirical formula: C₂H₅

    • condensed formula: CH₃CH₂CH₂CH₃

• Homologous Series: Same functional group

  • The boiling point increases as the carbon chain goes up

  • Refer to the Homologous chart

• For skeletal form: each point has a carbon atom

Naming Hydrocarbons

• Alkanes: name (longest), then alkyl groups

  • Arrange names of substituent groups in alphabetical order (ignoring prefixes)

    

• Alkenes: alk-x-ene

  • C=C (Double Bond)

    • Double bond starts at the lowest number

• Alkynes: alk-x-yne

  • CC (Triple Bond)

    • Triple bond starts at lowest number

• Halogen Alkane: x-halo alkane

  

Naming Oxygen-Containing Organic Compounds

• Alcohol: Alkan-x-ol (Methanol & ethanol no need for #)

• Ether: x-alkoxy alkane (treat alkoxy as substituent which is substituent with the lowest #)

  • give -OH the lowest #

    

• Aldehyde: alkanal, CHO is labelled #1

• Ketone: Alkan-x-one, C=O group give the lowest #

  • no need for # for propanone or butane

    

• Carboxylic acid: alkanoic acid, COOH is labelled #1

• Ester: carboxylic acid + alcohol

  • Alkyl alkanoate (alkyl for alcohol, alkanoate end for carboxylic acid side)

  • Numbering in the acid starts from C=O & alcohol starts from O-C group

    

Structual Isomers

• Primary, secondary & tertiary compounds

  • Depends on what the C attached to OH is attached to

  • 

• Structural Isomers: same molecular formula but different structural formula (atoms joined together differently)

• Branched-chain isomers (less surface area) have lower boiling points than straight chain isomers (high surface area, high london-dispersion forces)

Stereoisomers

• Same structural formula but atoms are arranged differently in space

  • Cis means same side

  • Trans means opposite side

• E/Z Priority rules (higher priority to atom attached to C=C with higher atomic #)

• Optical Isomers: When 4 different atoms/groups attached to a single carbon atom (Chiral)

  • Mirrors (enantiomers)

    

• Racemic mixture: Equimolar mixture of 2 enantiomers

Unit 2: Organic Reactions & Mechanisms

Reactions of Hydrocarbons

• Complete oxidation of a hydrocarbon

  • hydrocarbon + oxygen = carbon dioxide + water

    • C₆H₁₂ + 9O₂ (g) = 6CO₂ (g) + 6H₂O (l)

  • When oxygen supply is limited, a hydrocarbon will undergo incomplete combustion (only form carbon if O2 extremely limited)

    • C₃H_{8 (g)} + 2O_{2 (g)} = 3C_(g) +4H₂O_(l)

Free radical substitution mechanism

• Substitution of alkanes

  

Nucleophilic substitution reaction mechanism

• Nucleophilic substitution of halogenoalkanes

  • 

  • Nucleophiles: electron pair donors, attracted to electron deficient carbon atoms

  • Mechanisms

    • 1° halogenoalkane (SN2 Mechanism)

      rate = k [Rx][OH-]

      • inversion of configuration if a nucleophile attacks a chiral centre

    • 3° halogenoalkane (SN1 Mechanism)

      rate = k [RA]

      • not stereospecific - racemix mixture formed

    • 2° halogenoalkanes undergo a mixture of Sn1 and Sn2 mechanisms

    • Factors that affect the rate of nucleophilic substitution reaction

      • Identity of nucleophile (only Sn2 reaction affected)

        • Anions more reactive than neutral species

      • Identity of halogen (Sn1 & Sn2)

      • 1°, 2°, 3° halogenoalkane

        • Sn2 ratio is 1°>2°>3°

        • Sn1 rate is 3°>2°>1°

      • Choice of Solvent

Electrophilic addition mechanism

• Electrophile: electron-deficient species

  • Attracted to regions of relatively high electron density

    

  • Halogenation

    • reaction with Br₂

      • alkanes will have no reaction because it requires heat as a catalyst. therefore it will remain red

      • alkenes will go colourless because it does not require a catalyst

Markovnikov’s Rule

• if more than one product is possible, the more electronegative atom will end up on the carbon atom of the double cond that has fewer hydrogen

  

• the carbocation formed is one that has its positive charge on the most substituted carbon

Electrophilic substitution mechanism

• Electrophilic substitution of benzene

  

  • Step 1: Generation of nitronium iron (NO₂+)

    • Mixing nitric acid with sulphuric acid at SO°C generates a higher (NO2+) mechanism

  • Step 2: Rate determining step

    

  • Step 3:

    

• Addition polymerization of alkenes

Reactions of Oxygen-containing Compounds

Mild oxidation

• (Controlled oxidation of an alcohol to create other functional groups)

  

Reduction reactions

• (reverse oxidation reactions)

  • Reducing agents include lithium aluminum hydride (LiAlH₄ (This is stronger) and NaBH₄

    

• Reduction of Nitrobenzene

  

• Formation of ester (condensation reaction)

  

Organic Synthesis

Unit 3: Spectroscopy

IR Spectroscopy

• Index of hydrogen deficiency (IHO)

  • Double bond = 1

  • Triple bond = 2

  • Ring = 1

  • Aromatic ring = 4

  • IHO = ½ (2C + 2 - h - x + n)

• IR is absorbed by certain bonds causing them to stretch or bend

• Bond will only interact with IR radiation if it is polar

  • Match wavenumbers with bonds

• Fingerprint region (1500-650 cm^-1) difficult to interpret, lots of C-C & C-H bond vibrations

Mass Spectrometry

• Measures relative masses of atoms or ions

• Measures mass-to-change ratio of ions

• Ionization causes molecule to break up into different fragments

• Greatest mass peak is parent ion (Molecular mass)

  

‘H NMR Spectrometry

• Nuclei in different chemical environments produce different signals in the spectrum

• Signals are measured against the standard signal produced by TMS (8=0 ppm)

• Why TMS?

  • 12 protons, all in the same environment

  • Strong signal even when present in small amounts

  • Chemical shift value very low

• The area under a peak is proportional to the number of proton atoms in that environment

  • Integration trace distance/height of each step is ratio between # of protons in each environment

    

  • If there are n H’s on an adjacent atom, the signal for a particular proton will be split into n+1 peaks

    

  • Intensities of peaks are given by Pascal’s Triangle

    

  • example