Organic Chemistry: Radical Reactions, Synthesis, and Alcohol Chemistry Study Guide

Allylic Bromination (Page 495):
- This reaction involves the substitution of a hydrogen atom at the allylic position (the carbon atom adjacent to a double bond) with a bromine atom.
- This process typically proceeds via a radical mechanism.

Markovnikov vs. Anti-Markovnikov Regiochemistry:
- Markovnikov Addition (21): The rule stating that in the addition of a protic acid $HX$ to an asymmetric alkene, the acid hydrogen ( $H$ ) becomes attached to the carbon with fewer alkyl substituents, and the halide ( $X$ ) group becomes attached to the carbon with more alkyl substituents. Basically, the nucleophile adds to the more substituted carbon.
- Anti-Markovnikov Addition (1915): A reaction where the substituent is bonded to the less substituted carbon rather than the more substituted one. This is common in hydroboration-oxidation or radical-mediated additions of $HBr$ .
Elimination Paradigms:
- Zaitsev Elimination: A regioselective elimination reaction that favors the formation of the more substituted, and thus more stable, alkene.
- Hofmann Elimination (1991): An elimination reaction that yields the less substituted alkene (the Hofmann product). This typically occurs when using a sterically hindered or bulky base.

Dehydration of Alcohols:
- Reagents: $H_2SO_4$ and heat.
- The process involves the removal of a water molecule ( $H_2O$ ) from an alcohol to form an alkene.
Hydroboration-Oxidation:
- Step 1: $BH_3$ (or another borane source).
- Step 2: $NaOH$ and $H_2O_2$ .
- This sequence results in the anti-Markovnikov hydration of an alkene to produce an alcohol.
Reduction of Alkynes to Alkenes:
- Trans-alkene Formation: Uses dissolving metal reduction conditions, specifically $Na/NH_3(l)$ . This produces a linear, trans-alkene.
- Cis-alkene Formation: Uses catalytic hydrogenation with a poisoned catalyst, specifically $H_2$ and Lindlar's catalyst. This produces a cis-alkene.
Leaving Group Modification:
- Transformation: $OH \rightarrow OTs$ .
- Converting a hydroxyl group ( $OH$ ) into a tosylate group ( $OTs$ ) makes it a "good L.G." (leaving group) for subsequent substitution ( $S_N2$ ) or elimination reactions.

Catalytic Hydrogenation:
- Reagents: $H_2$ gas with a metal catalyst like $Pt$ , $Pd$ , or $Ni$ .
- Reduces alkenes and alkynes to alkanes, and can reduce various functional groups depending on conditions.
Reduction of Carbonyls:
- Sodium Borohydride ( $NaBH_4$ ) in $MeOH$ (Methanol): A mild reducing agent that specifically reduces aldehydes and ketones to primary and secondary alcohols, respectively. It is noted as having "no extra O" (likely referring to its inability to reduce carboxylic acids or esters, which contain more oxygen atoms).
- Lithium Aluminum Hydride ( $LiAlH_4$ ): A powerful reducing agent that "reduces everything," including aldehydes, ketones, esters, and carboxylic acids, to their corresponding alcohols.
Oxidation of Alcohols:
- PCC (Pyridinium Chlorochromate): A mild oxidant that converts primary alcohols to aldehydes and secondary alcohols to ketones without over-oxidizing to carboxylic acids.
- Jones Oxidation: Uses $Na_2Cr_2O_7$ (Sodium dichromate) in the presence of $H_2SO_4$ and $H_3O^+$ . This strong oxidizing agent converts primary alcohols all the way to carboxylic acids and secondary alcohols to ketones.

Grignard Reagent Preparation:
- General formula: $R-MgBr$ .
- Formation: Alkyl or aryl halide reacted with Magnesium metal ( $Mg^0$ ) in an ether solvent.
Reaction with Esters:
- Synthesis example: Reaction of an ester containing a methoxy group ( $OMe$ ) with a Grignard reagent ( $R-MgBr$ ).
- Step 1: The Grignard reagent attacks the carbonyl carbon twice.
- Step 2: Acidic workup ( $H_3O^+$ ).
- Product: A tertiary alcohol ( $OH$ ) where the original carbonyl carbon is now bonded to two functional groups provided by the Grignard reagent and one original alkyl group from the ester backbone.