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Organic Chemistry (IB)

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)

      • C3H8 (g) + 2O2 (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

ME

Organic Chemistry (IB)

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)

      • C3H8 (g) + 2O2 (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

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