OAT Organic Chemistry Reactions 5

Question 1

Which reaction is used to convert a primary amide to a primary amine with one fewer carbon (chain shortening)?

Accepted Answer

Hofmann rearrangement

Answer

The Hofmann rearrangement treats a primary amide with Br2/NaOH, causing migration of the R group to nitrogen and loss of CO2 to give a primary amine.

Question 2

What is the stereochemical result of bromine addition to (E)-2-butene?

Accepted Answer

Meso-2,3-dibromobutane

Answer

Anti addition of Br2 to (E)-2-butene through a bromonium ion gives the meso-2,3-dibromobutane because the two stereocenters are opposite but the molecule has an internal mirror plane.

Question 3

Which nucleophile is used in the Wittig reaction to convert a ketone into an alkene?

Accepted Answer

Phosphorus ylide (R3P=CH2)

Answer

A phosphorus ylide reacts with the carbonyl to form a four-membered oxaphosphetane that collapses to give an alkene and triphenylphosphine oxide.

Question 4

In the Fischer esterification, what is the role of the acid catalyst and excess alcohol?

Accepted Answer

The acid protonates the carbonyl oxygen to activate it toward nucleophilic attack, and excess alcohol drives equilibrium toward ester

Answer

The acid catalyst activates the carbonyl toward nucleophilic addition, and excess alcohol shifts the equilibrium toward product by Le Chatelier's principle.

Question 5

Which reaction converts a terminal alkyne to an aldehyde via anti-Markovnikov hydration?

Accepted Answer

Hydroboration-oxidation (9-BBN, then H2O2/NaOH)

Answer

Hydroboration of a terminal alkyne with a bulky borane followed by oxidation gives an aldehyde via anti-Markovnikov addition.

OAT - Optometry Admission Test Practice Test

OAT - Optometry Admission Test Practice Test

OAT Organic Chemistry Reactions 5