E-Z Isomerism Practice Questions Quiz and Flashcards

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Questions and Answers

What is the significance of the geometry of π– bonds in allenes?

It causes the groups attached to be in perpendicular planes

What causes a molecule to be chiral?

Having non-superimposable mirror images

Why is penta-2,3-diene considered a chiral molecule?

It has no chiral centers but has non-superimposable mirror images

Why do allenes with different substituents on the end atoms exhibit chirality?

Due to the perpendicular arrangement of the groups attached to the end atoms Signup and view all the answers

What is an example of a chiral molecule with two stereocenters but no chiral centers?

Allenes Signup and view all the answers

How are the pi-bonds in allenes oriented with respect to each other?

Perpendicular Signup and view all the answers

What is the essential requirement for keto-enol tautomerism to occur?

Presence of alpha-hydrogen atoms Signup and view all the answers

Why do benzaldehyde and benzophenone not show keto-enol tautomerism?

Absence of alpha-hydrogen atoms Signup and view all the answers

What are the products formed by the keto-form of a compound containing a carbonyl group?

Oximes, hydrazone, and DNP test positive (presence of C=O group) Signup and view all the answers

What is the difference between E-form and Z-form in terms of the arrangement of groups around a double bond?

E-form has same priority groups on opposite sides of the double bond, while Z-form has them on the same side. Signup and view all the answers

How can you calculate the percentage Enantiomeric Excess?

% Enantiomeric excess = (% moles of one enantiomer - % moles of other enantiomer) / (total moles of both enantiomers) × 100 Signup and view all the answers

How can the enolic form of a compound be detected?

By giving a color with neutral FeCl3 solution Signup and view all the answers

In Allenes, why are the groups attached to the end carbon atoms in perpendicular planes?

The planes of π-bonds of allenes are perpendicular to each other, causing the groups attached to the end C atoms to lie in perpendicular planes. Signup and view all the answers

What makes allenes with different substituents on the end carbon atoms chiral?

The unique geometry of the π-bonds in allenes, where the planes are perpendicular, leads to chirality. Signup and view all the answers

What conditions give rise to optical activity in Biphenyl Compounds?

When at least three of the 2, 2’, 6, and 6’ positions are occupied by sufficiently large groups, and free rotation about the single bond joining the two phenyl groups is restricted. Signup and view all the answers

What happens to the enolic form of a compound in Br2/CCl4 solution?

Decolourises (a test for unsaturation due to the presence of C=C bond) Signup and view all the answers

How does the presence of large substituent groups at the o and o’-positions in Biphenyl Compounds affect the molecule's optical activity?

The restricted rotation caused by the large substituents at these positions leads to optical activity in the molecule. Signup and view all the answers

Study Notes

E-Z Isomerism

E-form: When two same priority groups are present on the opposite side of a double bond, it is known as the E-form.
Z-form: When two same priority groups are present on the same side of a double bond, it is known as the Z-form.

Racemic Forms and Enantiomeric Excess

Enantiomeric excess (%) = ((moles of one enantiomer - moles of other enantiomer) / total moles of both enantiomers) * 100
Specific rotation (θ) = (observed specific rotation / specific rotation of the pure enantiomer) * 100

Optical Activity in Allenes

The planes of π-bonds of allenes are perpendicular to each other.
This geometry causes the groups attached to the end C atoms to lie in perpendicular planes.
Allenes with different substituents on the end C atoms are chiral.

Optical Activity of Biphenyl Compounds

When at least three of the 2,2’,6, and 6’ positions are occupied by sufficiently large groups, free rotation about the single bond joining the two phenyl groups is restricted.
This restricted rotation gives rise to optical activity due to the molecule being asymmetrical as a whole.

Allenes with Chiral Centers

Allenes with different substituents on the end C atoms are chiral.
Such allenes do not show cis-trans isomerism.
An example is penta-2,3-diene, which has no chiral centers but is a chiral molecule with two enantiomers.

Keto-Enol Tautomersm

Keto-enol tautomerism occurs in compounds with α-hydrogen atoms.
Examples of compounds that exhibit keto-enol tautomerism include butan-2-one and acetophenone.
Examples of compounds that do not exhibit keto-enol tautomerism include benzaldehyde and benzophenone due to the absence of α-hydrogen atoms.
Keto-forms form oximes, hydrazones, and give a positive DNP test.
Enolic-forms give a color with neutral FeCl3 solution, decolourise Br2/CCl4 solution, and form acetyl derivatives.

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Description

Test your knowledge on E–Z isomerism and enantiomeric excess with this quiz. Learn about the E–form and Z–form configurations, as well as how to calculate enantiomeric excess. Practice questions on specific rotation and optical activity.