What is retrosynthetic analysis?	Working backward from the target molecule to simpler starting materials. You identify the bonds that could have been formed last and determine what precursors are needed.
What does the retrosynthetic arrow (=>) mean?	It means 'can be made from.' Unlike a reaction arrow, it points backward from product to starting material. Target => Precursor.
When do you need a protecting group?	When a functional group would react with your intended reagent but you want it left untouched. Protect it before the reaction, then remove the protecting group afterward.
How do you protect an alcohol (-OH) group?	Convert it to a silyl ether using TBSCl or TMSCl. Remove later with fluoride (TBAF) or mild acid. This prevents the -OH from reacting with strong bases or nucleophiles.
How do you convert an alcohol to a better leaving group?	Convert -OH to a tosylate (TsCl, pyridine) or mesylate (MsCl, Et3N). These are much better leaving groups than -OH for substitution reactions.
How do you add one carbon to a chain?	Use a cyanide nucleophile (NaCN) in an SN2 reaction to add -CN, then reduce or hydrolyze. Alternatively, use a Grignard reagent with formaldehyde.
How do you add two carbons to a chain?	Use an acetylide anion (formed by treating a terminal alkyne with NaNH2) as a nucleophile in an SN2 reaction with a primary alkyl halide.
What is the Grignard reaction?	An organomagnesium reagent (RMgBr) attacks a carbonyl. With formaldehyde: gives primary alcohol. With aldehyde: gives secondary alcohol. With ketone: gives tertiary alcohol.
How do you convert an alkene to an anti-Markovnikov alcohol?	Hydroboration-oxidation (BH3/THF followed by H2O2/NaOH). The -OH adds to the less substituted carbon.
How do you convert an alkene to a Markovnikov alcohol?	Acid-catalyzed hydration (H2O/H2SO4) or oxymercuration-demercuration (Hg(OAc)2/H2O, then NaBH4). The -OH adds to the more substituted carbon.
How do you oxidize a primary alcohol to an aldehyde (without over-oxidation)?	Use PCC (pyridinium chlorochromate) in CH2Cl2. PCC is mild enough to stop at the aldehyde. Stronger oxidants like Jones reagent or KMnO4 will push it to the carboxylic acid.
How do you reduce a ketone or aldehyde to an alcohol?	Use NaBH4 (mild, selective for aldehydes/ketones) or LiAlH4 (stronger, also reduces esters and carboxylic acids). Both deliver hydride (H-) to the carbonyl carbon.
What is a functional group interconversion (FGI)?	Changing one functional group into another without altering the carbon skeleton. Example: oxidizing an alcohol to a ketone, or reducing an alkene to an alkane.
How do you form a carbon-carbon bond via aldol reaction?	Treat a ketone or aldehyde with base (LDA or NaOH) to form an enolate, which attacks another carbonyl. The product is a beta-hydroxy carbonyl (aldol product).
How do you convert a carboxylic acid to an ester?	Fischer esterification: heat the carboxylic acid with an alcohol in the presence of an acid catalyst (H2SO4). Reversible reaction driven by excess alcohol.
What is the Williamson ether synthesis?	An SN2 reaction between an alkoxide (RO-) and a primary alkyl halide to form an ether. Use a strong base (NaH) to deprotonate the alcohol first.
How do you plan a synthesis with multiple steps?	1) Identify the key bond or functional group that differs between starting material and product. 2) Work backward from the product. 3) Consider selectivity at each step. 4) Add protecting groups if needed.
When should you use SN2 vs. SN1 in a synthesis plan?	Use SN2 for primary substrates when you need inversion of stereochemistry and predictable regiochemistry. Use SN1 only when racemization is acceptable and the substrate is tertiary.
How do you convert a terminal alkyne to a trans alkene?	Use dissolving metal reduction (Na/NH3). This gives the trans (E) alkene selectively via an anti addition of hydrogen.
How do you convert a terminal alkyne to a cis alkene?	Use catalytic hydrogenation with Lindlar's catalyst (Pd/CaCO3 poisoned with lead acetate and quinoline). This gives the cis (Z) alkene via syn addition.