Optical Isomerism: General Exam Flashcards

Explain why Step 4 produces a racemic mixture.(answer applies to this type of question generally)

• Planar molecule

• Equal chance of attack from above or below

• Producing equal amounts of both enantiomers

6 Marker

-First stage of the mechanism drawn out(H-Br to the organic molecule):

• Produces two secondary carbocation intermediates

-Second stage of the mechanism drawn out(finish the mechanism)

• So two different optical isomers created as can be attacked from above or below

-Draw the planar structure of the carbocation and show it being attacked from above and below

• c) NaCN

Conditions: Ethanolic AND aqueous

Hint: Involves reduction instead of substitution!

H² and LiAlH⁴ with dry ether

Equation: 2NCCH₂CH₂CN + 4H₂/[8H] → H₂N(CH₂)4NH₂

To remember how to balance:

• All Cs not bonded to H get 2 Hydrogens each, which takes 4 away. This leaves 4(Creates two CH₂

• Then all the N gets two each, leaving none.

What is the general word equation for the hydrolysis of an Amide?

• Amide + H₂O + H⁺ (acid) → Carboxylic Acid + Ammonium Ion

• Amine group present(N-H)

• Amide group present(CONH)

The C=O group is a part of the amide group, not a ketone!

• C-N bond broken in the amide

• Leaving the Carboxylic acid as a product

• And the phenylamine picks up 2 more H due to protonation, forms R-N⁺H₃(ammonium ion)

• D

• This is because it is a symmetrical ketone.

• In these questions, look for symmetrical ketones,often right

2-Hydroxypropanenitrile displays optical isomerism. Draw three-dimensional representations of the two enantiomers of 2-hydroxypropanenitrile, showing how the two structures are related to each other.

State the definition of racemic mixture.

Equal mixture of enantiomers

Reduction: Look for unsymmetrical ketones or aldehydes!