Organics Week 3

Question 1

What is Fehling’s test?

Answer 1

Fehling’s test is a chemical test used to distinguish between aldehydes and ketones. It involves the reaction of an aldehyde with Fehling’s reagent, which is a solution of copper (II) sulfate, sodium hydroxide, and potassium sodium tartrate.

Question 2

What is meant by the process of dehydration?

Answer 2

Dehydration is a chemical reaction in which a water molecule is removed from a compound. In the context of alcohols, dehydration refers to the process of removing a water molecule from an alcohol to form an alkene.

Question 3

What is elimination?

Answer 3

Elimination is a chemical reaction in which a molecule loses atoms or groups of atoms to form a double bond or a new compound. In the context of alcohols, elimination refers to the process of removing a water molecule from an alcohol to form an alkene.

Question 4

What is Tollen’s test?

Answer 4

Tollens’ test is a chemical test used to distinguish between aldehydes and ketones. It involves the reaction of an aldehyde with Tollens’ reagent, which is a solution of silver nitrate in aqueous ammonia.

Question 5

How would you apply the dehydration reaction to convert but-1-ene into Z-but-2-ene or E-but-2-ene?

Answer 5

By using a dehydrating agent such as Al2O3 at 600K, a water molecule is removed from but-1-ene, resulting in the formation of Z-but-2-ene or E-but-2-ene.

Question 6

What is involved in the oxidation of alcohols and elimination processes?

Answer 6

The oxidation of alcohols and elimination processes involve the conversion of alcohols into aldehydes or carboxylic acids.

Question 7

What is the significance of converting alcohols into alkenes?

Answer 7

The conversion of alcohols into alkenes offers a potential way to create polymers without relying on oil-derived monomers.

Question 8

How would you apply the acid-catalyzed elimination process to convert propan-1-ol into propene?

Answer 8

By using a dehydrating agent such as Al2O3 at 600K, the water molecule is removed from propan-1-ol, resulting in the formation of propene.

Question 9

What are some commonly used reagents in the oxidation of alcohols and elimination processes?

Answer 9

Fehling’s solution and concentrated sulfuric or phosphoric acids are commonly used reagents in these reactions.

Question 10

What happens in dehydration reactions and what do they form?

Answer 10

Dehydration reactions can also occur, removing a water molecule from a compound and forming alkenes.

Question 11

If you have an unknown alcohol and you want to determine whether it is a primary or secondary alcohol, how would you apply the Tollens’ reagent test?

Answer 11

You would oxidize the alcohol to produce either an aldehyde or a ketone. Then, you would add the Tollens’ reagent. If a silver mirror forms on the inside of the test tube, the alcohol was a primary alcohol. If no reaction occurs, the alcohol was a secondary alcohol.

Question 12

How can primary and secondary alcohols be differentiated?

Answer 12

To differentiate between primary and secondary alcohols, specific reactions involving Tollens’ reagent, Fehling’s solution, and Benedict’s solution can be used.

Question 13

How can the oxidation of alcohols and elimination processes in chemistry be identified?

Answer 13

The oxidation of alcohols and elimination processes in chemistry can be identified by checking for the -OH group and conducting tests with phosphorus(V) chloride and potassium dichromate(VI) solution.

Question 14

What color change occurs when primary and secondary alcohols undergo oxidation?

Answer 14

When primary and secondary alcohols undergo oxidation, the color changes from orange to green.

Question 15

What is the purpose of the Fehling’s test and what is formed when an aldehyde reacts with Fehling’s solution?

Answer 15

The Fehling’s test is another method to detect aldehydes, where a brick red precipitate of copper(I) oxide is formed when an aldehyde reacts with Fehling’s solution.

Question 16

What is often involved in the elimination reactions of alcohols?

Answer 16

Acid catalysis is often involved in these elimination reactions.

Question 17

What does the Tollens’ test detect and how is it indicated?

Answer 17

The Tollens’ test is used to detect the presence of aldehydes in a solution, where a dark grey precipitate or silver mirror indicates the presence of aldehydes.

Question 18

What is high-resolution mass spectrometry?

Answer 18

High-resolution mass spectrometry is a technique that can accurately determine the molecular formula of a compound by measuring the precise mass of the molecular ion. This technique can measure mass values to five decimal places, allowing differentiation between compounds with similar molecular masses.

Question 19

What is the sodium carbonate test?

Answer 19

The sodium carbonate test is used to check for the presence of a carboxylic acid. When sodium carbonate is added to a carboxylic acid, it reacts to produce carbon dioxide gas, which is observed as effervescence or fizzing.

Question 20

What is a molecular ion?

Answer 20

The molecular ion is the peak in a mass spectrum that represents the intact molecule. It is formed when the organic molecule is ionized and has a charge of +1.

Question 21

What is Fehling’s solution (and what does it do)?

Answer 21

Fehling’s Solution is a reagent that contains blue Cu2+ ions. It is used to oxidize aldehydes, converting them into carboxylic acids.

Question 22

What is Tollen’s reagent (and what does it do)?

Answer 22

Tollens’ Reagent is a solution prepared by mixing aqueous ammonia and silver nitrate. It is used to oxidize aldehydes, converting them into carboxylic acids.

Question 23

What is mass spectrometry?

Answer 23

Mass spectrometry is an analytical technique used to determine the molecular mass and structure of organic compounds. When an organic molecule is analyzed in a mass spectrometer, it can break apart into fragments, producing a series of peaks.

Question 24

What happens when ions break up in mass spectrometry?

Answer 24

Fragmentation occurs when ions break up and produce lines in the mass spectrum, providing information for deducing the compound’s structure and identifying it.

Question 25

How can the presence of carboxylic acids be tested?

Answer 25

Sodium carbonate can be used to test for the presence of carboxylic acids. It will fizz and release carbon dioxide.

Question 26

What does the M+2 peak in mass spectra indicate?

Answer 26

The M+2 peak in mass spectra can indicate the presence of chlorine or bromine atoms due to naturally occurring isotopes.

Question 27

How can accurate masses of specific atoms be used in mass spectrometry?

Answer 27

Accurate masses of specific atoms can be calculated to differentiate between compounds with similar Mr values.

Question 28

How does high-resolution mass spectrometry distinguish between compounds with the same parent ion mass?

Answer 28

High-resolution mass spectrometry can distinguish between compounds with the same parent ion mass by measuring accurate atomic masses.

Question 29

If you have a solution and you suspect it contains an aldehyde, which reagent would you use to confirm your suspicion and what would be the observable reaction?

Answer 29

You would use Tollens’ Reagent or Fehling’s Solution. With Tollens’ Reagent, a silver mirror would form inside the test tube if aldehydes are present. With Fehling’s Solution, the blue Cu2+ ions in the solution would change into a red precipitate of Cu2O.

Question 30

What is the purpose of Tollens’ Reagent?

Answer 30

Tollens’ Reagent is used to oxidize aldehydes, forming carboxylic acids. It produces a silver mirror when aldehydes are present.

Question 31

What is the purpose of Fehling’s Solution?

Answer 31

Fehling’s Solution also oxidizes aldehydes, resulting in a red precipitate of copper(I) oxide.

Question 32

How can high-resolution mass spectrometry help in the study of compounds?

Answer 32

It can accurately determine the molecular formula of a compound by measuring the precise mass of the molecular ion

Question 33

How does high-resolution mass spectrometry determine the molecular formula of a compound?

Answer 33

High-resolution mass spectrometry accurately determines the molecular formula by measuring the precise mass of the molecular ion.

Question 34

What does the peak with the highest mass-to-charge ratio represent in mass spectrometry?

Answer 34

The original molecule that has not fragmented, known as the molecular ion ([M]+)

Question 35

What does the highest m/z peak represent in mass spectrometry?

Answer 35

In mass spectrometry, the highest m/z peak represents the intact molecule, known as the molecular ion.

Question 36

What is the wavenumber?

Answer 36

Wavenumber, measured in reciprocal centimeters (cm-1), is a unit used in infrared spectroscopy to represent the frequency of infrared radiation absorbed by a molecule. It is directly related to the energy of the absorbed radiation and can be used to identify specific bonds or functional groups based on their characteristic absorption frequencies.

Question 37

What is the fingerprint region (IR spec?

Answer 37

The fingerprint region, typically in the wavenumber range of 1500 to 400 cm-1, is a region of the infrared spectrum that contains complex overlapping vibrations of the atoms in a molecule. It is unique for each compound and can be used as a distinctive ‘fingerprint’ for identification purposes in infrared spectroscopy.

Question 38

What are impurities?

Answer 38

Impurities refer to unwanted substances or contaminants present in a sample. In the context of infrared spectroscopy, unexpected absorptions in the infrared spectrum may indicate the presence of impurities in the sample being analysed.

Question 39

What is the greenhouse effect?

Answer 39

The greenhouse effect is a natural process in which certain gases in the Earth’s atmosphere, such as carbon dioxide (CO2), methane (CH4), and water vapor (H2O), absorb and re-emit infrared radiation. This process traps heat in the atmosphere, leading to a warming effect.

Question 40

What is IR spectroscopy?

Answer 40

Infrared spectroscopy is a technique that involves the absorption of infrared radiation by specific groups within a molecule at distinct frequencies. It provides detailed information about the types of bonds present in a molecule and can be used to identify functional groups and detect impurities.

Question 41

How do the infrared spectra of ethanal, ethanol, and ethanoic acid relate to the greenhouse effect mechanism?

Answer 41

The infrared spectra of ethanal, ethanol, and ethanoic acid exhibit complex overlapping vibrations in the fingerprint region, which are responsible for the greenhouse effect mechanism

Question 42

What information does infrared spectroscopy provide about a molecule?

Answer 42

Infrared spectroscopy is a technique that provides information about the types of bonds in a molecule through the absorption of infrared radiation at distinct frequencies.

Question 43

How can a computer be used in infrared spectroscopy?

Answer 43

A computer can compare IR spectra against a database of known compounds to identify the compound.

Question 44

How can an IR absorption table be used in infrared spectroscopy?

Answer 44

The technique involves using an IR absorption table to deduce the presence or absence of specific bonds or functional groups.

Question 45

What is the role of the characteristic stretching and deformation vibrations in the infrared spectra of ethanal, ethanol, and ethanoic acid?

Answer 45

The characteristic stretching and deformation vibrations in the infrared spectra of ethanal, ethanol, and ethanoic acid provide information about the different functional groups present in these compounds.

Question 46

How is energy transferred in the atmosphere and what is the result?

Answer 46

Energy is transferred through collisions in the atmosphere, leading to atmospheric warming.

Question 47

How would you apply the knowledge of infrared spectroscopy to explain the greenhouse effect?

Answer 47

The greenhouse effect occurs when UV radiation from the sun passes through the atmosphere and heats the Earth’s surface. The Earth emits infrared long-wavelength radiation in response. C=O bonds in CO2 molecules absorb this infrared radiation, preventing it from escaping into space. This is similar to how bonds in infrared spectroscopy absorb infrared radiation.

Question 48

What can infrared spectroscopy help identify in a sample?

Answer 48

Infrared spectroscopy can help identify functional groups and detect impurities in a sample.

Question 49

What is the connection between the absorption of infrared radiation and the greenhouse effect?

Answer 49

The absorption of infrared radiation by certain bonds is the same process that contributes to the greenhouse effect in the atmosphere.

Question 50

What can rogue absorptions indicate in infrared spectroscopy?

Answer 50

Rogue absorptions may indicate the presence of unexpected impurities in the sample.

Question 51

How is the infrared spectrum below 1500 cm-1 used in identification?

Answer 51

The infrared spectrum below 1500 cm-1 is unique for each compound and can be used as a ‘fingerprint’ for identification.

Question 52

What type of reactions are C=O bonds in carbonyls less likely to undergo compared to C=C bonds in alkenes?

Answer 52

C=O bonds in carbonyls are less likely to undergo addition reactions compared to C=C bonds in alkenes.

Question 53

What property of aldehydes makes them easily oxidisable?

Answer 53

The presence of a hydrogen atom attached to the carbon-oxygen double bond in aldehydes makes them easily oxidisable.

Question 54

Can aldehydes be converted into carboxylic acids?

Answer 54

Yes, aldehydes can be converted into carboxylic acids.

Question 55

What is the outcome of reducing aldehydes with sodium borohydride in ethanol at room temperature and pressure?

Answer 55

The outcome is the conversion of aldehydes into primary alcohols, while ketones become secondary alcohols.

Question 56

What are the two main types of carbonyl compounds?

Answer 56

The two main types of carbonyl compounds are aldehydes and ketones.

Question 57

What is the result of oxidising aldehydes using potassium dichromate and dilute sulfuric acid under reflux conditions?

Answer 57

The result is the conversion of aldehydes into carboxylic acids.

Question 58

How do small carbonyls interact with water?

Answer 58

Small carbonyls can dissolve in water through interactions with water molecules, although they cannot directly bond with water.

Question 59

How do aldehydes and ketones differ in terms of their chemical structure?

Answer 59

Aldehydes have a C=O bond at the end of a carbon chain with an attached hydrogen, while ketones have a C=O bond in the middle of a carbon chain.

Question 60

What type of reactions are C=O bonds in carbonyls less likely to undergo compared to C=C bonds in alkenes?

Answer 60

C=O bonds in carbonyls are less likely to undergo addition reactions compared to C=C bonds in alkenes.

Question 61

What happens when aldehydes are oxidised using Tollens’ reagent?

Answer 61

Aldehydes produce a silver mirror, while ketones remain unchanged.

Question 62

What can potassium dichromate oxidise in the context of carbonyl compounds?

Answer 62

Potassium dichromate can oxidise alcohols and aldehydes to form carboxylic acids, with primary alcohols being converted to aldehydes and further to carboxylic acids, secondary alcohols being converted to ketones, and tertiary alcohols not undergoing oxidation.

Question 63

What is nucleophilic addition?

Answer 63

Nucleophilic addition is a reaction in which a nucleophile attacks an electron-deficient atom, resulting in the addition of a new group to a molecule. In the context of aldehydes and ketones, nucleophilic addition refers to the addition of a nucleophile to the carbonyl group, resulting in the formation of a new carbon-carbon bond.

Question 64

What is meant by trigonal planar?

Answer 64

Trigonal planar is a molecular geometry in which three atoms or groups are arranged symmetrically around a central atom, forming a flat, triangular shape. In the context of aldehydes and ketones, the carbonyl group is often in a trigonal planar arrangement, allowing nucleophiles to approach from both sides during nucleophilic addition reactions.

Question 65

What is NaBH4?

Answer 65

NaBH₄ is a reducing agent commonly used in organic chemistry. It provides hydride ions (H⁻) that can react with the positive carbon in the C=O bond of aldehydes and ketones through nucleophilic addition.

Question 66

What is a racemic mixture?

Answer 66

A racemic mixture is a mixture that contains equal amounts of two enantiomers, which are mirror images of each other. In the context of aldehydes and ketones reacting with HCN, the nucleophilic addition occurs from both sides of the carbonyl group, resulting in the formation of a racemic mixture of the corresponding hydroxynitriles.

Question 67

What is catalytic hydrogenation?

Answer 67

Catalytic hydrogenation is a reaction in which hydrogen gas (H₂) reacts with a compound in the presence of a catalyst to form a new product. In the context of aldehydes and ketones, catalytic hydrogenation refers to the reduction of the carbonyl group to form alcohols.

Question 68

What is 2.4-DNP?

Answer 68

2,4-Dinitrophenylhydrazine (2,4-DNP) is a reagent commonly used to test for the presence of aldehydes and ketones. It reacts with the carbonyl group, forming an orange solid.

Question 69

How does HCN react with unsymmetrical aldehydes and ketones?

Answer 69

When HCN reacts with unsymmetrical aldehydes and ketones, it forms a racemic mixture by approaching the trigonal planar carbonyl group from both sides.

Question 70

Why are HCN, potassium cyanide (KCN), and sodium cyanide (NaCN) difficult to handle safely?

Answer 70

HCN, potassium cyanide (KCN), and sodium cyanide (NaCN) are toxic and difficult to handle safely.

Question 71

Why is it important to understand carbonyls, their names, how they dissolve, and their reactions?

Answer 71

Understanding carbonyls, their names, how they dissolve, and their reactions is crucial for A-level chemistry.

Question 72

What are some methods to manipulate aldehydes and ketones?

Answer 72

Aldehydes and ketones can be reduced using NaBH₄ or catalytic hydrogenation, identified using 2,4-DNP, and reacted with HCN to form hydroxynitriles.

Question 73

What is the role of dilute sulfuric acid (H2SO4) in the reaction of aldehydes and ketones with hydrogen cyanide to form hydroxynitriles?

Answer 73

Supplies the necessary H+ ions in the second step of the mechanism

Question 74

What are the roles of NaCN and H2SO4 in the reaction of HCN with carbonyls?

Answer 74

In this reaction, NaCN provides the nucleophilic CN- ions, and H2SO4 supplies the necessary H+ ions in the second step of the mechanism.

Question 75

How can carbonyls be reduced using catalytic hydrogenation?

Answer 75

Carbonyls can be reduced using hydrogen and nickel catalyst under high pressure in catalytic hydrogenation, which is another method to reduce carbonyls.

Question 76

What is the purpose of 2,4-DNP in the reaction with aldehydes and ketones?

Answer 76

2,4-DNP reacts with aldehydes and ketones, forming an orange solid, and the melting point of the solid helps identify the carbonyl compound.

Question 77

What is the rule for naming aldehydes and ketones?

Answer 77

When naming aldehydes and ketones, the longest carbon chain must include the carbon in the -CN group, and the carbon attached to nitrogen is considered carbon number 1.