Organic Chemistry Mechanisms and Reactions
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Questions and Answers

What type of mechanism is involved in the formation of a racemate as described?

  • Nucleophilic substitution
  • SN2 mechanism
  • Electrophilic addition
  • SN1 mechanism (correct)

A racemate formed in SN1 mechanism exhibits optical activity.

False (B)

What is produced when a haloalkane reacts via an SN1 mechanism?

A racemate

In the SN1 mechanism, the first step involves the formation of a __________ intermediate.

<p>planar carbocation</p> Signup and view all the answers

Match the following descriptions with the correct mechanisms:

<p>SN1 = Leads to optical inactivity due to racemate formation SN2 = Inverse stereochemistry at the reaction site</p> Signup and view all the answers

What is formed when aldehydes react with Fehling’s Solution?

<p>Carboxylic acids (B)</p> Signup and view all the answers

Ketones react with Tollen’s reagent to produce a silver mirror.

<p>False (B)</p> Signup and view all the answers

What type of alcohol do aldehydes reduce to when treated with reducing agents such as NaBH4?

<p>Primary alcohols</p> Signup and view all the answers

When ketones are treated with reducing agents like LiAlH4, they are reduced to __________.

<p>secondary alcohols</p> Signup and view all the answers

Match the following reagents with their corresponding reaction outcomes:

<p>Fehling’s Solution = Oxidation of aldehydes to carboxylic acids Tollen’s reagent = Formation of a silver mirror NaBH4 = Reduction of carbonyls to alcohols LiAlH4 = Reduction of aldehydes to primary alcohols</p> Signup and view all the answers

What prefix is used for compounds that contain a ketone group in addition to a carboxylic acid?

<p>oxo- (A)</p> Signup and view all the answers

A compound with carboxylic acid groups on both ends of the chain is called a mono-dioic acid.

<p>False (B)</p> Signup and view all the answers

What is the name for the compound: C2H2O4?

<p>Ethanedioic acid</p> Signup and view all the answers

Esters are named using a bit ending in –yl from the __________ and –anoate from the __________.

<p>alcohol, carboxylic acid</p> Signup and view all the answers

Match the following compound names with their corresponding groups:

<p>Ethanedioic acid = Dioic acid 2-oxopropanoic acid = Ketone and carboxylic acid Butanenitrile = Nitrile 2-hydroxy-2-methylpropanenitrile = Nitrile with additional hydroxyl and methyl groups</p> Signup and view all the answers

Which naming convention is correct for a nitrile compound?

<p>It ends in –nitrile, counting the C of the CN as the last carbon. (C)</p> Signup and view all the answers

The stem of the name for butanenitrile includes 'butan' and does not end with 'nitrile'.

<p>False (B)</p> Signup and view all the answers

What is the main feature of ester nomenclature?

<p>Esters are named using a part from the alcohol and a part from the carboxylic acid.</p> Signup and view all the answers

What phenomenon causes signals in high resolution H NMR to be split into further lines?

<p>Spin-Spin coupling (C)</p> Signup and view all the answers

Nuclei in identical chemical environments will show spin-spin coupling in H NMR.

<p>False (B)</p> Signup and view all the answers

What is the effect of inequivalent hydrogen atoms on neighboring carbon atoms in H NMR spectroscopy?

<p>It causes spin-spin coupling and leads to the splitting of signals.</p> Signup and view all the answers

In high resolution H NMR, individual signals are affected by spin-spin coupling among ________ on neighboring carbon atoms.

<p>hydrogens</p> Signup and view all the answers

Match the following concepts related to H NMR with their descriptions:

<p>Spin-Spin coupling = Splitting of NMR signals due to neighboring hydrogens Nuclei in identical environments = Do not exhibit spin-spin coupling Chemical shift = Variation in resonance frequency due to the electronic environment High resolution H NMR = Data collection that provides detailed signal splitting</p> Signup and view all the answers

Which solvent is a good choice for non-polar organic molecules?

<p>CCl4 (A)</p> Signup and view all the answers

CDCl3 is a non-polar solvent suitable for polar organic molecules.

<p>False (B)</p> Signup and view all the answers

What compound is added to a sample to calibrate the NMR spectrum?

<p>TMS</p> Signup and view all the answers

The measure of how far the frequency of the proton signal has shifted from TMS is known as the chemical ______.

<p>shift</p> Signup and view all the answers

Match the following solvents with their properties:

<p>CCl4 = Good for non-polar organic molecules CDCl3 = Good for polar organic molecules TMS = Inert and used for calibration H2O = Polar solvent for many reactions</p> Signup and view all the answers

Which of the following is a reason TMS is used for calibration?

<p>It provides a strong signal with a single peak (D)</p> Signup and view all the answers

The δ scale is a measure in parts per thousand (ppt).

<p>False (B)</p> Signup and view all the answers

What does a greater shift in δ indicate about nearby atoms or groups?

<p>More electronegative groups give a greater shift.</p> Signup and view all the answers

What does the peak with the largest m/z value in a mass spectrum represent?

<p>The parent ion or molecular ion (B)</p> Signup and view all the answers

The molecular ion is formed when an organic molecule loses an electron.

<p>True (A)</p> Signup and view all the answers

What is the relationship between the charge of the ion and the mass/charge ratio in mass spectrometry?

<p>The mass/charge ratio equals the molecular weight when the charge is +1.</p> Signup and view all the answers

Fragmentation occurs due to the breaking of __________ bonds.

<p>covalent</p> Signup and view all the answers

Match the following types of ions with their characteristics:

<p>Molecular ion = Parent ion with largest m/z Fragment ion = Produced from the molecular ion Carbocation = Relatively stable positive ion Free radical = Species with an unpaired electron</p> Signup and view all the answers

Which of the following statements is true regarding the intensity of peaks in a mass spectrum?

<p>The more stable the ion, the greater the peak intensity. (C)</p> Signup and view all the answers

Free radicals are formed directly from fragment ions.

<p>False (B)</p> Signup and view all the answers

The molecular ion for butane, C4H10, is shown as [__________]+.

<p>C4H10</p> Signup and view all the answers

Flashcards

Naming Carboxylic Acids

The carboxylic acid group (-COOH) is prioritized for numbering carbon atoms in the chain.

Naming Dioic Acids

Carboxylic acids with two carboxyl groups (-COOH) on either end of the chain are called dioic acids.

Naming Nitriles

The carbon atom of the nitrile group (-CN) is counted as the first carbon in the chain.

Naming Nitriles (Stem)

Be mindful of the nitrile stem prefixes in naming nitrile compounds.

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Naming Esters (part 1)

The part of the ester name ending in '-yl' comes from the alcohol used.

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Naming Esters (part 2)

The part ending in '-anoate' comes from the carboxylic acid.

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Oxo-prefix in Naming

The prefix "oxo-" is used for compounds with a ketone and carboxylic acid.

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Prioritize Carboxylic Acid

In naming organic compounds, carboxylic acid groups are the highest priority, influencing numbering, especially di-carboxylic chains.

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Racemate formation

A mixture of equal amounts of enantiomers resulting in no optical activity.

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SN1 Mechanism

A reaction mechanism where a carbocation intermediate is formed, followed by nucleophilic attack.

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Enantiomers

Non-superimposable mirror image molecules.

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SN2 Mechanism

A reaction mechanism with no intermediates, occurring directly as a single transition state.

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Optical activity

The ability of a chiral molecule to rotate plane-polarized light.

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Fehling's Test

A chemical test that distinguishes aldehydes from ketones. Aldehydes are oxidized by Fehling's solution, forming a red precipitate of Cu2O. Ketones do not react.

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Tollen's Test

A chemical test that distinguishes aldehydes from ketones. Aldehydes are oxidized by Tollen's reagent, forming a silver mirror on the inside of the test tube. Ketones do not react.

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Reducing Agents

Chemicals that donate electrons to another molecule, causing it to gain electrons (be reduced). Common reducing agents used for carbonyls include NaBH4 (sodium tetrahydridoborate) and LiAlH4 (lithium tetrahydridoaluminate).

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Reduction of Carbonyls

The process of adding hydrogen atoms to a carbonyl group, converting it to an alcohol. Aldehydes are reduced to primary alcohols, and ketones are reduced to secondary alcohols.

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LiAlH4

Lithium aluminum hydride, a powerful reducing agent used to reduce carbonyls to alcohols. It reacts with water, so it must be used in dry ether.

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Spin-Spin Coupling

In high-resolution H NMR, signals can be split into multiple lines due to interactions between non-equivalent hydrogen atoms on neighboring carbon atoms.

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Chemical Environment

The surrounding atoms and bonds influence an atom's magnetic environment, leading to unique chemical shifts in H NMR.

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Identical Chemical Environments

Atoms in identical chemical environments do not exhibit spin-spin coupling with each other.

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δ (Delta) Value

The chemical shift in H NMR describes the position of a signal on the spectrum, indicating the magnetic environment of the proton.

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High Resolution H NMR

A technique that reveals fine details in the spectrum, including spin-spin coupling and subtle chemical shift differences.

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What makes CCl4 a good solvent?

CCl4 (carbon tetrachloride) is a non-polar compound, making it an excellent solvent for non-polar organic molecules due to the principle of 'like dissolves like'.

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Why is CDCl3 a good solvent?

CDCl3 (chloroform) is a polar covalent molecule, making it an effective solvent for polar organic molecules.

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What is TMS used for in NMR?

Tetramethylsilane (TMS) is added to NMR samples to calibrate the spectrum. It provides a reference point for measuring the chemical shifts of other protons in the molecule.

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Why is TMS a good calibration standard?

TMS is a suitable NMR calibration standard because it gives only one signal, its signal is far from other proton signals, it provides a strong signal, is inert, and easily removed.

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What is the chemical shift (δ)?

The chemical shift (δ) in NMR spectroscopy refers to the difference in ppm (parts per million) between the resonance frequency of a proton and the reference frequency of TMS.

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What influences chemical shift?

The chemical shift (δ) of a proton in NMR is influenced by the electronegativity of neighboring atoms or groups. More electronegative groups lead to a greater shift.

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What is ppm in NMR?

Parts per million (ppm) is the unit used to express the chemical shift in NMR spectroscopy. It is a relative scale that indicates how far the proton signal has shifted away from TMS.

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Molecular Ion

The ion formed when a molecule loses an electron in a mass spectrometer. It represents the complete molecule and has the highest mass-to-charge ratio (m/z) in the spectrum.

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Fragmentation

The process where a molecular ion breaks down into smaller ions and neutral fragments in a mass spectrometer. This results in multiple peaks in the spectrum.

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What causes fragmentation?

Fragmentation occurs when covalent bonds in the molecular ion break due to the energy absorbed during ionization. The stability of the resulting ions influences the peak intensities.

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What information does the mass spectrum provide?

The mass spectrum provides information about the molecular weight of the molecule (from the molecular ion peak) and the structure of the molecule (from the fragmentation pattern).

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How does the stability of a fragment ion affect the peak?

More stable fragment ions are likely to form, leading to higher peak intensities in the mass spectrum. This is because stable ions are less likely to break down further.

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Parent Ion

Another term for the molecular ion. This peak corresponds to the intact molecule before any fragmentation.

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What does m/z represent?

m/z represents the mass-to-charge ratio of an ion. It's a key parameter used to identify and analyze ions in mass spectrometry.

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How is the molecular weight determined from the mass spectrum?

The molecular weight of a molecule is determined by the m/z value of the molecular ion (or parent ion) peak in the mass spectrum. The charge is usually +1, so the m/z is essentially the molecular weight.

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Study Notes

Carbonyls, Carboxylic Acids and Chirality

  • Homologous series: A series of organic compounds with a similar structure, differing only by the addition of a -CH₂- group.
  • Alkenes: Hydrocarbons with carbon-carbon double bonds. Suffix -ene, example ethene.
  • Alcohols: Organic compounds containing a hydroxyl (-OH) group. Suffix -ol, example propan-1-ol.
  • Halogenoalkanes: Organic compounds containing a halogen atom (Cl, Br, I). Prefix chloro, for example 1-chloropropane.
  • Aldehydes: Carbonyls with the carbonyl group at the end of the carbon chain. Suffix -al, example ethanal.
  • Ketones: Carbonyls with the carbonyl group in the middle of the carbon chain. Suffix -one, example propanone.
  • Carboxylic acids: Organic compounds containing a carboxyl (-COOH) group. Suffix -oic acid, example ethanoic acid.
  • Nitriles: Contain a cyano group (-C≡N). Suffix -nitrile, example propanenitrile.
  • Amines: Contain an amino group (-NH₂). Suffix -amine, example propylamine.
  • Esters: Formed from a carboxylic acid and an alcohol. Have an -oate suffix, example methyl ethanoate.
  • Acyl chlorides: Formed from carboxylic acids and chlorine. Suffix -oyl chloride, example ethanoyl chloride.
  • Amides: Contain a carbonyl group and an amino group. Suffix -amide, example ethanamide.

Chirality

  • Asymmetric carbon: A carbon atom bonded to four different groups.
  • Enantiomers: Non-superimposable mirror images of each other.
  • Racemic mixture: A 50/50 mixture of enantiomers. Neither rotate plane-polarized light.

Reactions of Carbonyls

  • Oxidation of aldehydes: Aldehydes can be oxidized to carboxylic acids using potassium dichromate (VI) solution and dilute sulfuric acid. Aldehydes are oxidized, but ketones aren't.
  • Fehling's solution: A test solution used to identify the presence of aldehydes (blue to red precipitate).
  • Tollen's reagent: A test to show if an aldehyde is present (silver precipitate).
  • Reduction of carbonyls: Reducing agents (LiAlH₄) transform aldehydes to primary alcohols and ketones to secondary alcohols.
  • Addition of hydrogen cyanide to Carbonyls: Forms hydroxynitriles when carbonyls react with HCN and KCN.

Carboxylic Acids

  • Acidity: Carboxylic acids are weak acids, slightly dissociating in water and capable of releasing CO₂ from carbonates.
  • Delocalisation: The pi-electron cloud involved in C-O bond delocalization stabilizes carboxylates, making them capable of forming salts.

Esterification

  • Mechanism: Carboxylic acids and alcohols react in the presence of a strong acid catalyst to form esters and water.
  • Uses: Esters commonly used as scents and flavors.

Acyl Chlorides

  • Reactivity: Acyl chlorides are more reactive than carboxylic acids in substitution reactions.
  • Reactions with water: Acyl chlorides undergo reactions with water to form carboxylic acids and hydrochloric acid.
  • Reactions with alcohol: Acyl chlorides form esters when reacted with alcohols.
  • Reactions with ammonia: Acyl chlorides form primary amides when reacted with ammonia.
  • Reactions with primary amines: Acyl chlorides form secondary amides when reacted with primary amines.

Polyesters

  • Condensation polymer: Formed by the combination of monomers with the release of a small molecule such as water.
  • Properties: Polyesters often used for clothing and other applications.

Spectroscopy and Chromatography

  • NMR Spectroscopy: Determines the number and arrangement of hydrogen atoms in a molecule.
  • Mass spectrometry: Breaks apart molecules to determine their mass-to-charge ratio (m/z).
  • TLC (Thin-Layer Chromatography): Separates components in a mixture based on their relative solubility in a mobile phase and a relatively stationary phase.

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15. Carbonyls, Carboxylic Acids and chirality IGCSE PDF

Description

Test your knowledge on various organic chemistry mechanisms such as SN1 and the reactions involving aldehydes and ketones. This quiz covers important concepts like optical activity in racemates and the outcomes of different chemical reagents. Challenge yourself with matching descriptions and identifying reaction products.

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