Evaluative coursework 2

Question 1

What are the functional groups concerned?

Answer 1

1.Alkenes (C=C).2.Alcohols:- Primary alcohols (R-CH2OH).- Secondary alcohols (R-CH(OH)-R’).- Tertiary alcohols (R-R’C(OH)-R’’).3.Carbonyls:- Aldehydes (R-CHO).- Ketones (R-CO-R’).4. Carboxylic acids.5.Esters.6.Amines.7.Benzene:- Benzene.- Phenols.

Question 2

What is the 2,4-Dinitrophenylhydrazine(2,4-DNPH) test used for?

Answer 2

To test for the presence of a carbonyl group.

Question 3

How is the 2,4-DNPHtest carried out and what are the observations?

Answer 3

Test: Compound in question is added to 2,4-DNPH in Brady’s reagent (2,4-DNPH with methanol and sulfuric acid)Observations: Orange precipitate forms if carbonyl group present.

Question 4

How are individual carbonyls distinguished from 2,4-DNPH test?

Answer 4

Orange 2,4-DNPH derivative from the test purified using recrystallisation and then melting point analysis performed on the yellow/orange crystal. Melting point then compared to those of known derivatives from database.

Question 5

What would be the consequence of using impure 2,4-DNPH derivative crystals in melting point analysis?

Answer 5

1. Melting point is lower.2. Melting range is wider.

Question 6

What is the carbonate test used for?

Answer 6

To test for the presence of carboxylic acid.

Question 7

How is the carbonate test carried out and what are the observations?

Answer 7

Test: Solid carbonate (e.g. CaCO3) or aqueous carbonate (e.g. NaHNO3) added to solution of compound in question.Observations: Effervescence produced if carboxylic acid present.

Question 8

What is the general formula for the carbonate test?

Answer 8

2R-COOH + CO32-→ 2R-COO-+ CO2+ H2OR-COOH + HCO3-→ R-COO-+ CO2+ H2O

Question 9

What is the acidified dichromate (VI) test used for?

Answer 9

To test for the presence of primary/secondary alcohol/aldehyde.

Question 10

How is the dichromate (VI) test carried out and what are the observations?

Answer 10

Test: Compound in question is heated under reflux with a mixture of K2Cr2O7and conc. H2SO4.Observations: The orange solution should turn green if primary/secondary alcohol/aldehyde present.

Question 11

What are the general formulae for the dichromate (VI) test?

Answer 11

R-CH2OH + 2[O]→ R-COOH + H2OR-CH(OH)-R’ + [O]→ R-CO-R’ + H2OR-CHO + [O]→ R-COOH

Question 12

Why should the dichromate (VI) not be used in excess?

Answer 12

The excess orange dichromate (VI) that doesn’t react will make the green colour change difficult to see.

Question 13

What is the Tollen’s reagent test used for?

Answer 13

To distinguish an aldehyde from a ketone.

Question 14

How is Tollen’s reagent made?

Answer 14

Aqueous AgNO3is mixed with NaOH and the Ag2O precipitate formed is redissolved in dilute aqueous ammonia.

Question 15

How is the the Tollen’s reagent test carried out and what are the observations?

Answer 15

Test: The 2,4-DNPH test needs to be used to determine that the compound in question is a carbonyl. Then, asmall amountof Tollen’s reagent is gently heated with the compound in question for a few minutes in a test tube.Observations: If ‘silver-mirror’ forms on side of test tubes, the compound is an aldehyde

Question 16

What is the general formula for the Tollen’s reagent test?

Answer 16

R-CHO + [O]→ R-COOH

Question 17

What is the bromine water test used for?

Answer 17

To test for the presence of alkene groups.

Question 18

How is the bromine water test carried out and what are the observations?

Answer 18

Test: Compound in question mixed with bromine water and the mixture is shaken vigorously.Observations: If alkene present, bromine water is decolourised.

Question 19

What is the general formula for the bromine water test?

Answer 19

R-C=C-R’ + Br2→ R-CBr=CBr-R’

Question 20

How can infrared spectroscopy be used to identify a compound?

Answer 20

1. The absorption peaks give a good indication of what bonds are in the compound and thus what functional groups coupld be in the compound.2. The fingerprint region on the spectra may be compared with a database of spectra from known compounds to identify which compound is responsible.

Question 21

How can mass spectroscopy be used to identify a compound?

Answer 21

1. M+ peaks represents the relative molecular mass of the compound.2. Fragmentation can give us information on the structure of the compound.3. Fragmentation pattern is specific for a certain compound so can be compared to a database of spectra for known compounds.

Question 22

How can13C NMR be used to identify a compound?

Answer 22

1. The number of peaks represent the number of different bonding environments present in the compound.2. The chemical shift of the peaks tell us the types of carbon environments present in the compound, which gives a good indication for the functional groups present in the compound.3. Can be compared to a database of spectra of known compounds to find possible identity.

Question 23

How can1H NMR be used to identify a compound?

Answer 23

1. Number of peak sets represent the number of different hydrogen bonding environments present in the compound.2. Chemical shift of the peak sets indicate the types of hydrogen environments present in the compound which relates to the functional groups present in the compound.3. The splitting of the peak sets give us information on the number of hydrogens on adjacent carbon atoms.4. The integration (area under each peak) is proportional to the actual number of hydrogens found in each environment.