Optical Isomers Questions
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Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C5H10O
plane polarised light entaominoers rotates light in opposite directions
Isomer F is the active compound in the medicine ibuprofen. In the manufacture of ibuprofen both isomers F and G are formed. An enzyme is then used to bind to isomer G and catalyse its hydrolysis. After the products of hydrolysis of G are removed, a pure sample of isomer F is collected. Explain how a structural feature of this enzyme enables it to catalyse the hydrolysis of isomer G but not the hydrolysis of isomer F.
enzyme has an active site G entamioner complementary to active site
Give the IUPAC name of CH3CH2CH2CH2CH(OH)CN
2-hydroxyhexanenitrile
Describe how you would distinguish between separate samples of the two stereoisomers of CH3CH2CH2CH2CH(OH)CN
plane polarised light entamioners rotate light in opposite directions
Explain why the reaction produces a racemic mixture.
planar carbonyl group gets attacked from either side with equal probability produces equal amounts of enantiomers
Name the type of structural isomerism shown by the isomers of C5H12
Chain
Hemiacetals and acetals are compounds formed by the reaction of aldehydes with alcohols, such as the reaction of ethanal with ethanol. name the mechanism
nucleophillic addition
Explain the meaning of the term racemic mixture.
Equal mixture of enantiomers/optical isomers
State the relationship between two chiral molecules with the same structural formula.
mirror images
This question is about an organic synthesis. CH3CH2CH=CH2 -> CH3CH2CHBrCH3 -> Compound J Name the mechanism in Step 1. State the reagent(s) used for Step 1. Identify compound J. State the reagent(s) and conditions needed for Step 2. State the reagent(s) used for Step 4. Explain why Step 4 produces a racemic mixture. .
mechanism - Electrophillic Addition reagent - Hbr compound J - Butan-2-ol reagent - NaOH and warm aqueous solution reagent step 4 - HCN planar carbonyl group Equal chance (50/50) attack from above/below Giving equal amounts of both optical isomers/enantiomers
Identify the reagent that is warmed with isomer W in reaction 2. (3-bromopropanenitrile) State the other reaction condition needed.
KCN aqueous and ethanol
state the reagent and reaction conditions needed for reaction 3. Give an equation for reaction 3.
H2 and Ni NCCH2CH2CN + 4H2 → H2N(CH2)4NH2
an incomplete equation for the formation of nylon 4,6 from five molecules of butane-1,4-diamine and five molecules of hexanedioic acid is shown. Deduce the values of x and y in this equation.
x = 5 y = 9
Explain why a racemic mixture does not rotate plane-polarised light
Equal amounts of both enantiomers rotate light in opposite directions, so the effects cancel out.
what is an enantiomer
non-superimposable mirror images
what is an optical isomer
non-superimposable mirror images
butanone reacts with reagent S to form compound T which exists as a racemic mixture. Dehydration of T forms U, C5H7N, which can represent a pair of geometrical isomers. State the meaning of the term racemic mixture and suggest why such a mixture is formed in this reaction identify reagent S, and draw a structural formula for each of T and U.
50:50 mixture of equal enantiomers formed because C=O group is planar and there are equal chances that it gets attacked from the either side HCN
An isomer of CH3CH2CH2CH2CHO reacts with KCN followed by dilute acid to form a compound that does not show stereoisomerism. Draw the structure of the compound formed and justify why it does not show stereoisomerism.
Does not contain a chiral centre
6 MARKS - By considering the mechanism of the reaction, explain why the product has no effect on plane polarised light. 6 MARKS
there is a nucleophille attacking the planar carbonyl group which attacks the planar C=O group from either side with equal probability This product exists in 2 chiral forms there are also equal enantiomers formed equal amounts of both enantiomers rotate plane polarised of light in opposite directions therefore the effect cancels out because its an equal/racemic mixture
some students were asked to suggest methods to distinguish between isomers Q and R. One student suggested testing the optical activity of the products formed when Q and R were reacted separately with HCN. By considering the optical activity of these products formed from Q and R, explain why this method would not distinguish between Q and R
Product from Q is a racemic mixture/equal amounts of enantiomers racemic mixture is inactive or inactive explained Product from R is inactive (molecule) or has no chiral centre
Give the name of each of the circled functional groups labelled J and K on the structure of atenolol shown above. Functional group labelled J = Functional group labelled K =
J amide K secondary amine
the 1H n.m.r. spectrum of atenolol was recorded. One of the peaks in the 1H n.m.r. spectrum is produced by the CH2 group labelled p in the structure of atenolol. Use Table 2 on the Data Sheet to suggest a range of δ values for this peak. Name the splitting pattern of this peak. Range of δ values.
3.7 doublet
n.m.r. spectra are recorded using samples in solution. The 1H n.m.r. spectrum was recorded using a solution of atenolol in CDCl3 Suggest why CDCl3 and not CHCl3 was used as the solvent.
solvent must be proton free
suggest why CDCl3 is a more effective solvent than CCl4 for polar molecules such as atenolol.
CDCL3 is polar