Organic Chemistry Reactions for Final Exam

Alkene Reactions

Reaction with Hydrobromic Acid (HBr)

• Mechanism: Alkene (nucleophile) reacts with HBr (electrophile).
• Product: Major product formed by attaching hydrogen to primary carbon, forming a stable secondary carbocation.
• Bromide Attack: Occurs from front or back, leading to a racemic mixture.

HBr with Peroxides vs. Without

• Without Peroxides: Markovnikov rule applies, bromine attaches to the more substituted carbon (tertiary).
• With Peroxides: Anti-Markovnikov, bromine attaches to the least substituted carbon (primary).

Cyclohexene Reactions

• Br2 with Dichloromethane: Anti-addition occurs, producing a mixture of two stereoisomers.
• NBS Reaction: Radical reaction replacing allylic hydrogen with bromine.

Alkyne Reactions

Reduction Reactions

• H2 with Platinum Catalyst: Reduces to an alkane.
• Sodium Metal and Liquid Ammonia: Yields a trans alkene.
• Lindlar's Catalyst: Stops at a cis alkene.

Hydroboration-Oxidation of Alkynes

• Terminal Alkynes: Produces aldehydes via tautomerization from enols.
• Internal Alkynes with Mercury Sulfate: Forms ketones.

Substitution and Elimination Reactions

SN2 vs SN1

• SN2 Reaction: Occurs in polar aprotic solvents, e.g., with potassium iodide and acetone.
• SN1 Reaction: Occurs in polar protic solvents, e.g., water, leading to racemic mixtures.

E1 and E2 Reactions

• E1 Reaction: Occurs with secondary alcohols heated with acids, often leading to Zaitsev's product.
• E2 Reaction: Strong bases facilitate elimination to the most stable alkene (Zaitsev's product).

Alcohol Reactions

Alcohols with HX

• Primary Alcohols with HI: Proceed via SN2 mechanism.
• Secondary Alcohols: Typical SN1 mechanism, leading to racemic mixtures.

Oxidation of Alcohols

• Primary Alcohols: Oxidized to aldehydes by PCC and to carboxylic acids by chromic acid.
• Secondary Alcohols: Oxidized to ketones.
• Tertiary Alcohols: Generally resistant to oxidation.

Reducing Agents

Sodium Borohydride (NaBH4)

• Reduces aldehydes and ketones to alcohols.

Lithium Aluminum Hydride (LiAlH4)

• Reduces aldehydes, ketones, esters, and carboxylic acids to alcohols.

Grignard Reagents

• Reaction with Carbonyls: Convert ketones and aldehydes to alcohols by adding alkyl groups.

Important Notes

• Stereochemistry: Many reactions involve considerations of stereochemistry (cis/trans, syn/anti-addition).
• Carbocation Rearrangements: Stability of carbocations can lead to shifts (e.g., hydride shifts) for more stable intermediates.
• Practice Resources: Additional practice can be found via linked resources, such as video explanations and practice tests.