Module 6 Flashcards
(22 cards)
Explain what is meant by the term optical isomers
Optical isomers are non-super imposable mirror images
What is meant by the term isoelectric point
The pH at which the amino acid exists as a zwitterion
Explain why amines can behave as bases
The amine behaves as a base in its chemical reactions as the lone pair of electrons sited on the nitrogen atom can accept a proton.
What is an α-amino acid?
Both NH2 and COOH are bonded/attached to the same carbon atom.
What is a chiral carbon?
Carbon with four different groups attached.
State the property of α-amino acids that allow them to be separated by TLC.
Adsorption
Explain the use of two deuterated compounds in NMR spectroscopy.
CDCl3 used as a solvent
D2O used to identify OH OR NH protons
Explain what is meant by the term condensation polymer
Monomers join/react/form polymer/form chain AND another product/small molecule/H2O/HCl.
Suggest two benefits of using single stereoisomers in the synthesis of drugs
no/fewer side effects
increases the (pharmacological) activity/effectiveness
Explain how GC–MS enables the products to be identified
Gas chromatography separates the components/compounds.
Mass Spec is used to Identify compounds by comparison with a (spectral) database.
Why is TMS used for NMR?
TMS (tetramethylsilane) is the standard for chemical shift measurements.
Describe a method to obtain a pure sample and how to check its purity
Recrystallisation:
Dissolve impure solid in minimum volume of hot water/solvent
Cool solution and filter solid
Wash with cold water/solvent and dry
Obtain melting point
Compare to known values
Pure sample will have a (sharp) melting point very close to data book value.
At what temperature does the mono-substitution of a single NO₂⁺ electrophile take place?
It takes place when the reaction temperature is 55°C. At temperatures greater than this, multiple substitutions can occur on the benzene ring.
What is an enantiomer?
An enantiomer is one of a pair of optical isomers that are mirror images of each other and are non-superimposable, and are unique due to their effect on plane-polarised light. Each enantiomer rotates plane polarised light in opposite directions.
What is used as the reagent along with a H⁺ source to provide the HCN (hydrogen cyanide) for a nucleophilic addition reaction?
NaCN (sodium cyanide) is often used as the reagent along with an H⁺ source to provide the HCN (hydrogen cyanide). This is because HCN is hard to store and is a toxic gas which reacts to produce dangerous byproducts.
What is Tollens Reagent?
Tollens reagent is ammoniacal silver nitrate. It oxidises the aldehyde to a carboxylic acid and reduces silver ions to silver in the presence of an aldehyde. The silver can be seen deposited on the edge of the test tube. This is sometimes described as a silver mirror.
The reaction of a metal with a carboxylic acid will produce…
the corresponding salt and hydrogen gas.
What is preferred as a reagent in alcohol esterification?
Acid anhydrides can also be used to esterify alcohols. This occurs in an addition-elimination mechanism. Acid anhydrides react less vigorously than acyl chlorides and do not produce toxic HCl as a side product. As a result, they are often preferred as a reagent in esterification.
Do carbonates react with (a) carboxylic acids and (b) phenol?
(a) yes - effervescence as CO2 is formed
(b) no reaction observed
How do you produce an ester from a carboxylic acid?
Alcohol + (conc.) H2SO4
A student monitors the course of a reaction using thin-layer chromatography (TLC).
Outline how TLC could be used to monitor the course of the reaction.
Take samples from reaction mixture at regular intervals.
Spot/run on a TLC plate, alongside x and y controls.
Evidence to disprove Kekulé model
Lack of reactivity of benzene - it should decolorise bromine water, but it does not. So no C=C bonds.
Lengths of C-C bonds in benzene - All the bonds were the same length, whereas a single bond and a double bond have different lengths.
Hydrogenation enthalpies - Kekule structure estimated to have three times enthalpy change of cyclohexene, but it does not. Enthalpy of hydrogenation less exothermic than expected.
